SECTION 1

GENERAL

CONTENTS
Group 1 Specifications
Specifications............................................ T1-1-1
Working Range (Backhoe) ........................ T1-1-3
Working Range (BE Backhoe) .................. T1-1-4
Working Range (Loading Shovel) ............. T1-1-5
Engine ...................................................... T1-1-6
Engine Accessories .................................. T1-1-9
Hydraulic Devices ..................................... T1-1-9
Electrical Equipment ............................... T1-1-12

Group 2 Component Layout

Main Components ..................................... T1-2-1
Electrical System Components (1) ............ T1-2-2
Electrical System Components (2) ............ T1-2-3
Electrical System Components (3) ............ T1-2-8
Electrical System Components (4) ............ T1-2-9
On and Around Pumps............................ T1-2-10
Others..................................................... T1-2-11

18ET-1-1
(Blank)

18ET-1-2
 GENERAL / Specifications
SPECIFICATIONS

A
C

E
D

I H
G F

M183-11-001

Model EX1200-5C Hydraulic Excavator

BE Backhoe
Backhoe
Type of Front-End Attachment [7.55 m (24’9”) BE boom,
[9.1 m (29’10”) boom, 3.4 m (11’2”) arm]
3.4 m (11’2”) BE arm]
Bucket Capacity (Heaped) PCSA 5.0 m3 (6.5 yd3), CECE 4.4 m3 PCSA 6.5 m3 (8.5 yd3)
Operating Weight 108000 kg (238000 lb) 109000 kg (243000 lb)
Basic Machine Weight 80500 kg (177500 lb)
Engine CUMMINS QSK23 567 kW/1650 min-1 (771 PS/1650 rpm)
A: Overall Width 5430 mm (17 ft 10 in)
B: Cab Height 4320 mm (14 ft 2 in)
C: Rear End Swing Radius 4850 mm (15 ft 11 in)
D: Minimum Ground Clearance 990 mm (3 ft 3 in) (Excluding shoe lug)
E: Counterweight Clearance 1790 mm (5 ft 10 in)
F: Undercarriage Length 6410 mm (21 ft 0 in)
G: Undercarriage Width 4610 mm (15 ft 2 in)
H: Sprocket Center to Idler
5000 mm (16 ft 5 in)
Center
I: Track Shoe Width 710 mm (28 in) (Grouser shoe)
Ground Pressure 136 kPa (1.39 kgf/cm2, 19.7 psi) 137 kPa (1.40 kgf/cm2, 19.9 psi)
Swing Speed 5.8 min-1 (rpm)
Travel Speed (Fast/Slow) 3.5/2.4 km/h (2.2/1.6 mph)
Gradeability 35° (tanθ = 0.70)

T1-1-1
 GENERAL / Specifications

A C

E
D

I
H
G F

T183-01-01-002

Model EX1200-5C Hydraulic Excavator

Type of Front-End Attachment Loading Shovel
Bucket Capacity (Heaped) PCSA 6.5 m3 (8.5 yd3)
Operating Weight 111000 kg (245000 lb)
Basic Machine Weight 80900 kg (178400 lb)
Engine CUMMINS QSK23 567 kW/1650 min-1 (771 PS/1650 rpm)
A: Overall Width 5430 mm (17 ft 10 in)
B: Cab Height ∗5410 mm (17 ft 9 in)
C: Rear End Swing Radius 4850 mm (15 ft 11 in)
D: Minimum Ground Clearance 990 mm (3 ft 3 in) (Excluding shoe lug)
E: Counterweight Clearance 1790 mm (5 ft 10 in)
F: Undercarriage Length 6410 mm (21 ft 0 in)
G: Undercarriage Width 4610 mm (15 ft 2 in)
H: Sprocket Center to Idler
5000 mm (16 ft 5 in)
Center
I: Track Shoe Width 710 mm (28 in) (Grouser shoe)
Ground Pressure 139 kPa (1.42 kgf/cm2, 20.2 psi)
Swing Speed 5.8 min-1 (rpm)
Travel Speed (Fast/Slow) 3.5/2.4 km/h (2.2/1.6 mph)
Gradeability 35° (tanθ = 0.70)
NOTE: ∗The standard specification of loading shovel is equipped with an elevated cab.

T1-1-2
 GENERAL / Specifications
WORKING RANGE (BACKHOE)

C
B

A´

A M183-11-002

Boom Length 9.10 m (29′ 10″)

Arm Length 3.40 m (11′ 2″)
A : Maximum Digging Reach 15340 mm (50′ 4″)
A’ : Maximum Digging Reach (on ground) 15000 mm (49′ 3″)
B : Maximum Digging Depth *9340 mm (30′ 8″)
C : Maximum Vertical Wall *7620 mm (25′ 0″)
D : Maximum Cutting Height *13490 mm (44′ 3″)
E : Maximum Dumping Height *8920 mm (29′ 3″)
NOTE: ∗ The dimensions do not include the height of the shoe lug.

T1-1-3
 GENERAL / Specifications
WORKING RANGE (BE BACKHOE)

C
B

A´

A M183-11-003

Boom Length 7.55 m (24′ 9″) BE boom

Arm Length 3.40 m (11′ 2″) BE arm
A : Maximum Digging Reach 13760 mm (45′ 2″)
A’ : Maximum Digging Reach (on ground) 13380 mm (43′ 11″)
B : Maximum Digging Depth *7940 mm (26′ 1″)
C : Maximum Vertical Wall *5080 mm (16′ 8″)
D : Maximum Cutting Height *12300 mm (40′ 4″)
E : Maximum Dumping Height *8020 mm (26′ 4″)
NOTE: ∗ The dimensions do not include the height of the shoe lug.

T1-1-4
 GENERAL / Specifications
WORKING RANGE (LOADING SHOVEL)

H
E
G

E´

A
B
C

D
T183-01-01-003

A : Minimum Digging Distance 4460 mm (14′ 8″)

B : Minimum Level Crowding Distance 6520 mm (21′ 5″)
C : Level Crowding Distance 4340 mm (13′ 10″)
D : Maximum Digging Reach 11440 mm (37′ 6″)
E : Maximum Cutting Height *12350 mm (40′ 6″)
E’ : Maximum Dumping Height *8740 mm (28′ 8″)
F : Maximum Digging Depth *5240 mm (17′ 2″)
G : Working Radius at Maximum Dumping Height *6090 mm (20′ 0″)
H : Maximum Bucket Opening Width 1880 mm (6′ 2″)
NOTE: ∗ The dimensions do not include the height of the shoe lug.

T1-1-5
 GENERAL / Specifications
ENGINE
MAIN SPECIFICATIONS
Manufacturer .............................................CUMMINS
Model.........................................................QSK23
Type...........................................................Diesel, 4 cycle, vertical, 6-cylinder inline, water-cooled, turbo
charged, inter-cooled, direct injection type
Cyl. No.-bore×stroke .................................6-170 mm×170 mm (6.7 in×6.7 in)
Piston displacement ..................................23150 cm3 (1412 in3)
Rated output (SAE J1995) (GROSS) ....567 kW/1650 min-1 (771 PS/1650 rpm)
(NET) ..........538 kW/1650 min-1 (731 PS/1650 rpm)
Dry weight .................................................2565 kg (5655 lb)
Firing order ................................................1-5-3-6-2-4
Rotation direction ......................................Clockwise (view from fan side)

COOLING SYSTEM
Cooling fan ................................................Dia. 1219 mm (48 in), draw-in type
Fan pulley ratio..........................................0.7 : 1
Thermostat ................................................Cracking temp. : 77 °C (170 °F)
(under atmospheric pressure) .................Full open temp. : 90 °C (194 °F)
Water pump ...............................................Centrifugal swirl type

LUBRICATION SYSTEM
Lubrication pump type ...............................Gear pump
Oil filter ......................................................Full-flow paper element type with bypass function
Oil pan capacity.........................................70 L (18.5 US gal)

STARTING SYSTEM
Voltage⋅Output...........................................24 V⋅7.5 kW×2

PRE-HEAT SYSTEM
Type...........................................................Air heater

ENGINE STOP SYSTEM

Stop method ..............................................Fuel cut system with solenoid valve

ALTERNATOR
Type...........................................................AC generator with diode rectifier
Voltage⋅Output...........................................24 V⋅75 A

FUEL SYSTEM
Injection pump ...........................................CUMMINS HPI electronic contrl
Governor ...................................................Electronic all speed control

T1-1-6
 GENERAL / Specifications
PERFORMANCE
Lubrication oil consumption.......................0.27 g kW⋅h (New engine, at rated horsepower)
Fuel consumption ratio (GROSS)..............200 g/kW⋅h (147 g/PS⋅h)
Max. output torque (GROSS)..............3580 N⋅m (365 kgf⋅m, 2641 lbf⋅ft) @ 1350±100 min-1
Max. no load speed .............................1850±50 min-1

T1-1-7
 GENERAL / Specifications
ENGINE PERFORMANCE CURVE
Test Conditions: 1. THIS PERFORMANCE IS APPLIED UNDER CONDITIONS OF 25°C (AMBIENT TEMPERA-
TURE).
100 kPa (750mmHg) (ATMOSPHERIC PRESSURE) AND 1kPa (7.5mmHg) VAPOR PRES-
SURE.
2. WITH MUFFLER, AIR CLEANER, WITHOUT FAN

Max. Torque (Gross)

3472Nm/1350rpm

Rated power (Gross)

567kw/1650rpm

Min. BSFC (Gross)

204g/kwh

T18E-01-01-002

T1-1-8
 GENERAL / Specifications
ENGINE ACCESSORIES
RADIATOR ASSEMBLY
Type...........................................................Radiator/Inter-cooler tandem type assembly
Weight .......................................................350 kg (772 lb)

Radiator Inter-cooler
Core type...................................................Corrugated fin Corrugated fin
Capacity.....................................................63 L (17 US gal) -
Air-tight testing pressure ...........................196 kPa 980 kPa
(2.0 kgf/cm2, 28 psi) (10 kgf/cm2, 142 psi)
Cap opening pressure...............................88.2 kPa -
(0.9 kgf/cm2, 12.8 psi)

BATTERY
Capacity.....................................................176 Ah (5 hours)
Voltage.......................................................12 V×2
Weight .......................................................66 kg (146 lb)×2

Fuel Cooler
Weight .......................................................6.81 kg (15 lb)
Core type...................................................Corrugated
Capacity.....................................................3.3 L (0.87 US gal)
Air-tight testing pressure ...........................1.5 MPa (15 kgf/cm2, 218 psi)

HYDRAULIC DEVICES

PUMP DEVICE
Type...........................................................Spur gear
Gear speed ratio (Engine: Main pump) ....1 : 1.083
(Engine: Triple pump) ...1 : 1.106

MAIN PUMP
Model.........................................................K3V280SH11RL
Type...........................................................Variable displacement swash plate type plunger pump:
regulator attached type
Max. flow (Theoretical value) ....................500 L/min (132 US gpm)×3

3-UNIT PUMP
(OIL COOLER FAN MOTOR DRIVE PUMP)
Model.........................................................K3V63S
Type...........................................................Variable displacement swash plate type plunger pump:
Regulator attached type
Max. flow (Theoretical value) ....................115 L/min (30.3 US gpm)

(PILOT PUMP)
Model.........................................................KFP3228
Type...........................................................Gear pump
Max. flow (Theoretical value) ....................51.1 L/min (13.5 US gpm)

(TRANSMISSION LUBRICATION OIL PUMP)

Model.........................................................KP1015
Type...........................................................Gear pump
Max. flow (Theoretical value) ....................27.1 L/min (7.2 US gpm)

T1-1-9
 GENERAL / Specifications
MAIN CONTROL VALVE
Model.........................................................UH36-403
Type...........................................................Pilot pressure operated type (4-spool+5-spool)
Main relief pressure...................................Normal: 31.4 MPa (310 kgf/cm2, 4410 psi)
@340 L/min (89.7 US gpm)
High Lift: 33.3 MPa (340 kgf/cm2, 4830 psi)
@90 L/min (23.7 US gpm)

Overload relief pressure ..........................33.3 MPa (340 kgf/cm2, 4830 psi) @110 L/min (29.0 US gpm)
(Boom, Arm roll-in (BH) / Arm extend (LD), Bucket,
Bucket open (LD))
34.3 MPa (350 kgf/cm2, 4980 psi) @110 L/min (29.0 US gpm)
(Arm roll-out (BH)/ Arm retract (LD))
17.7 MPa (180 kgf/cm2, 2560 psi) @500 L/min (132 US gpm)
(Bucket close (LD))
When jack-up prevention switch is ON:
9.8 MPa (100 kgf/cm2, 1420 psi) @110 L/min (29.0 US gpm)
(Boom Lower)

SWING CONTROL VALVE

Model.........................................................UH36B2T1C2A2-3
Type...........................................................Pilot pressure operated type (4-spool)
Main relief valve ........................................31.4 MPa (320 kgf/cm2, 4550 psi)
@170 L/min (44.9 US gpm)
Overload relief valve..................................31.4 MPa (320 kgf/cm2, 4550 psi)
@110 L/min (29.0 US gpm)

SWING DEVICE
Type...........................................................Two-stage planetary reduction type

SWING MOTOR
Model.........................................................M2X210 CAB-10A
Type...........................................................Swash-plate type, fixed displacement plunger motor

SWING BRAKE VALVE

Type...........................................................Non counter balance valve type
Relief pressure ..........................................29.4 MPa (300 kgf/cm2, 4270 psi)

SWING PARKING BRAKE

Type...........................................................Multiple-wet-plate negative type
Cracking pressure for release ...................2260+590-0 kPa (23+6-0 kgf/cm2, 327+85-0 psi)

TRAVEL DEVICE
Type...........................................................Three-stage planetary reduction gear

TRAVEL MOTOR
Model.........................................................MSF-340VP-EH
Type...........................................................Swash-plate type, variable displacement plunger motor

TRAVEL BRAKE VALVE

Type...........................................................Counter balance valve type
Relief pressure ..........................................29.4±1 MPa (300±10 kgf/cm2, 4266±142 psi)

T1-1-10
 GENERAL / Specifications
TRAVEL PARKING BRAKE
Type...........................................................Multiple-wet-plate negative type
Cracking pressure for release ...................1.8 MPa (18 kgf/cm2, 256 psi)

CYLINDER

(BACKHOE)
Boom Arm Bucket (3.4 m Arm)
Rod Dia. ....................................................160 mm (6.30”) 180 mm (7.09”) 160 mm (6.30”)
Cylinder Bore.............................................230 mm (9.06”) 260 mm (10.24”) 230 mm (9.06”)
Stroke ........................................................2075 mm (6’ 10”) 2205 mm (7’ 3”) 1790 mm (5’ 10”)
Fully retracted length.................................3170 mm (10’ 5”) 3385 mm (11’ 1”) 2895 mm (9’ 6”)
Plating thickness .......................................30 µm (1.18 µin) 30 µm (1.18 µin) 30 µm (1.18 µin)
or more or more or more

Bucket Bucket Bucket

(BE) (For 4.5 m Arm) (For 5.8 m Arm)
Rod Dia. ....................................................170 mm (6.70”) 160 mm (6.30”) 130 mm (5.12”)
Cylinder Bore.............................................240 mm (9.45”) 230 mm (9.06”) 190 mm (7.48”)
Stroke ........................................................1790 mm (5’ 10”) 1790 mm (5’ 10”) 1555 mm (5’ 1”)
Fully retracted length.................................2895 mm (9’ 6”) 2895 mm (9’ 6”) 2385 mm (7’ 10”)
Plating thickness .......................................30 µm (1.18 µin) 30 µm (1.18 µin) 30 µm (1.18 µin)
or more or more or more

(LOADING SHOVEL)
Boom Arm Level
Rod Dia. ....................................................160 mm (6.30”) 150 mm (5.91”) 160 mm (6.30”)
Cylinder Bore.............................................230 mm (9.06”) 215 mm (8.46”) 230 mm (9.06”)
Stroke ........................................................2075 mm (6’ 10”) 1835 mm (6’ 0”) 790 mm (2’ 7”)
Fully retracted length.................................3170 mm (10’ 5”) 2785 mm (9’ 2”) 1815 mm (5’ 11”)
Plating thickness .......................................30 µm (1.18 µin) 30 µm (1.18 µin) 30 µm (1.18 µin)
or more or more or more

Bucket Bucket open/close

Rod Dia. ....................................................150 mm (5.91”) 140 mm (5.51”)
Cylinder Bore.............................................200 mm (7.87”) 85 mm (3.34”)
Stroke ........................................................1 600 mm (5’ 3”) 475 mm (1’ 7”)
Fully retracted length.................................3 405 mm (11’ 2”) 1 090 mm (3’ 7”)
Plating thickness .......................................30 µm (1.18 µin) 30 µm (1.18 µin)
or more or more

FRONT ATTACHMENT PILOT VALVE

Model.........................................................HVP06A-040-101

TRAVEL PILOT VALVE

Model.........................................................HVP05F-040-101

BUCKET OPEN / CLOSE PILOT VALVE (LOADING SHOVEL)

Model.........................................................HVP05H-040-101

SOLENOID VALVE UNIT

Solenoid valve (Function) ........................⋅ SA : Pump power decreasing (For pump 3)
⋅ SB : Pump power decreasing (For pump 1, 2)
⋅ SC : Boom mode selection
(Max. input flow) ..............50 L/min (13 US grm)
Pilot relief valve .........................................3.9 MPa (40 kgf/cm2, 570 psi)

T1-1-11
 GENERAL / Specifications
FLOW REDUCING SOLENOID VALVE
Function.....................................................Flow reducing
Max. input flow ..........................................60 L/min (15.8 US gal)

TRAVEL MODE SHIFT SOLENOID VALVE

Function.....................................................Travel mode shifting
Max. input flow ..........................................30 L/min (7.9 US gal)

2-SPOOL EHC VALVE

Function.....................................................Power increase solenoid valve ST: Speed sensing control
Max. input pressure...................................3.9 MPa (40 kgf/cm2, 570 psi)
Control pressure........................................Solenoid Valve ST: 0 to 2.7 MPa (0 to 27.5 kgf/cm2, 0 to 391 psi)
Function.....................................................Oil cooler fan control solenoid valve SF
Max. input pressure...................................3.9 MPa (40 kgf/cm2, 570 psi)
Control pressure........................................Solenoid Valve SF: 0 to 1.4 MPa (0 to 13.9 kgf/cm2, 0 to 198 psi)

OIL COOLER
Weight .......................................................725 kg (1600 lbf)
Core type...................................................Plate fin
Capacity .................................................... -
Air-tight testing pressure ...........................980 kPa (10 kgf/cm2, 142 psi)

OIL COOLER FAN MOTOR

Function.....................................................A2FM63
Displacement.............................................63 cm3/rev
Max Motor speed.......................................1400 min-1 (rpm) @ Engine 1650 min-1 (rpm)
Relief valve................................................21.6 MPa (220 kgf/cm2, 3130 psi)

OIL COOLER BYPASS CHECK VALVE

Cracking pressure .....................................245 kPa (2.5 kgf/cm2, 36 psi) at 40 L/min (11 US gpm)

ELECTRICAL EQUIPMENT
BATTERY RELAY
Voltage⋅Current .........................................24 V⋅100 A

STARTER RELAY 1
Voltage⋅Current .........................................24 V⋅180 A

STARTER RELAY 2
Voltage⋅Current .........................................24 V

LOAD DUMP RELAY

Voltage⋅Current .........................................24 V⋅10 A

HORN
Specifications ............................................24 V⋅2.3 A, 330 Hz

LIGHT
Specifications ............................................Work lights : halogen 24 V⋅70 W

T1-1-12
 GENERAL / Specifications
AIR CONDITIONER
Refrigerant.................................................134 a
Cooler capacity..........................................19.73 MJ/h (4600 kcal/h)
Cooler air flow ...........................................550 m3/h (720 yd3/h) or more
Heater capacity .........................................21.0 MJ/h (5000 kcal/h) or more
Temperature control ..................................Electronic control
Refrigerant quantity ...................................Std. cab : 1250±50 g (2.76±0.1 lb)
Elevated cab : 1300±50 g (2.87±0.1 lb)
Compressor oil quantity ............................220 cm3 (0.23 US qt)
(After replacement of the compressor, high pressure hose,
condenser, receiver tank, liquid hose, or air conditioner unit, the
compressor oil quantity is added.)

T1-1-13
 GENERAL / Specifications
(Blank)

T1-1-14
 GENERAL / Component Layout
MAIN COMPONENTS
Backhoe
2 3
1
4
5
6
7
8
36
9
37
10
11
12
13
14
31 15
16

30

29

28
27
26
Loading Shovel 4
5 25
32 24 17
3 23 18
2
22 19
1
31 6 21 20
35
30

33

34
T183-01-02-016

1- Bucket Cylinder 11 - Swing Device 20 - Swing Bearing 29 - Accumulator

2- Arm 12 - Main Control Valve 21 - Travel Device 30 - Travel Pilot Valve
3- Arm Cylinder 13 - Oil Cooler 22 - Upper Roller 31 - Bucket
4- Boom 14 - Oil Cooler Fan Motor 23 - Lower Roller 32 - Level Cylinder
(Loading Shovel Only)
5 - Boom Cylinder 15 - Intercooler 24 - Swing Control Valve 33 - Pilot Valve (Bucket Open)
(Loading Shovel Only)
6 - Front / Swing Pilot Valve 16 - Radiator 25 - Center Joint 34 - Pilot Valve (Bucket Close)
(Loading Shovel Only)
7 - Hydraulic Oil Tank 17 - Engine 26 - Track Adjuster 35 - Bucket Open/Close
Cylinder
(Loading Shovel Only)
8 - Battery 18 - Pump Device 27 - Pilot Shut-Off Valve 36 - Condenser
(Air Conditioner)
9 - Fuel Tank 19 - Signal Control Valve 28 - Front Idler 37 - Fuel Cooler
10 - Auto-Lubrication Device

T1-2-1
 GENERAL / Component Layout
ELECTRICAL SYSTEM COMPONENTS (1)
2
3
Overall Layout 4
5
6
1
7
8
11
9
10
34
12 Refer to T1-2-12
(Refer to T1-2-4)
13

14
33

32
14

31
30
29
(Refer to T1-2-3) 15
16 (Refer to T1-2-10)
28 17 (Refer to T1-2-10)
(Refer to T1-2-11) 27 18 (Refer to T1-2-10)
26
19 (Refer to T1-2-8)
25
24 20
(Refer to T1-2-11) 23
22 21 T18E-01-02-009
1 - Work Light (on Cab Roof) 10 - Fresh Air Sensor 19 - Engine Speed Sensor 1 28 - Hydraulic Oil Level Switch
(Air Conditioner) (Pump) 1, 2
2 - Monitor 11 - Fuel Temperature 20 - Engine Speed Sensor 2 29 - DC/DC Converter
(ECM)
3 - Quick Idle Switch 12 - Coolant Level Switch 21 - Pump Transmission Oil 30 - Horn Switch
Pressure Switch
4 - Work Light 13 - Coolant Temperature Sensor 22 - Oil Pressure Sensor 31 - Work Light
(at the right side of Frame) (Under Cab Floor)
5 - Starter Relay 1 14 - Air Cleaner Restriction Switch 23 - Pilot Pressure Sensor 32 - Sunlight Sensor
(All)
6 - Battery 15 - Starter 24 - Travel Mode Control 33 - Step Light
Solenoid Valve
7 - Battery Relay 16 - Solenoid Valve Unit 25 - Heavy Lift Solenoid Valve 34 - Electrical Equipment
Box
8 - Horn 17 - Flow Rate Decrease 26 - Hydraulic Oil
Solenoid Valve Temperature Sensor
9 - Fuel Sensor 18 - 2-Spool EHC Valve 27 - Pilot Pressure Sensor
(Travel)

T1-2-2
 GENERAL / Component Layout
ELECTRICAL SYSTEM COMPONENTS (2)

In the Cab

3 1
6 7 8 9 T18E-01-02-010

3 1

2
4

5 M18E-01-009

T18E-01-02-013

1 - 12 V Power Source 4 - Buzzer Cancel Switch 6- Engine Fault Code Display 8- Fault Diagnosing Switch B
Terminal Panel
2 - DC-DC Converter 5 - Travel Alarm Stop 7 - Fault Diagnosing Switch A 9- DLU Check Switch
Switch (Optional)
3 - MC Display Selection
Switch

T1-2-3
 GENERAL / Component Layout
Electrical Equipment Box

1 2 3 4 5 6 7 8 9 10

28

27

26

25

24 11

23

22

21 20 19 18 17 16 15 14 13 12

T18E-01-02-003

1 - Flow Rate Decrease 8 - *Engine Stop Indicator 15 - Main Controller A 22 - Work Light Relay 2
Solenoid Valve Relay Relay (Lower)
2 - *Quick Idle Relay 9 - *Engine Warning Indicator 16 - Main Controller B 23 - Washer Relay
Relay (Upper)
3 - Auto-Lubrication Relay 10 - DLU 17 - Fuse Box 1 24 - Upper Wiper Relay 2
4 - Preheat Indicator Relay 11 - *ECM Relay 18 - Fuse Box 2 25 - Upper Wiper Relay 1
5 - *Coolant Lever Switch 12 - Power Transistor 3 19 - Step Light Relay 26 - Lower Wiper Relay
Relay
6 - *Auto-Idle Relay 13 - Power Transistor 2 20 - Load Dump Relay 27 - Horn Relay
7 - *Engine Protection Relay 14 - Power Transistor 1 21 - *Engine Stop Relay 28 - Work Light Relay 1
NOTE: The items with mark ”*” are not used for the machine equipped with CUMMINS engine.

T1-2-4
 GENERAL / Component Layout
(Blank)

T1-2-5
 GENERAL / Component Layout

Around Batteries

1 2

12 13 3
10 11

4
5
6

9
8 7 T183-01-02-015

1- Air Heater Signal Relay 5- Battery Relay 2 8 - Fusible Link 8 (125A) 11 - Fusible Link 3 (75A)
2- Starter Relay 1 6- 1 Pole Junction 9 - Fusible Link 6 (100A) 12 - Fusible Link 2 (75A)
3- Battery Relay 1 7- Fusible Link 7 (125A) 10 - Fusible Link 4 (45A) 13 - Fusible Link 1 (45A)
4- Fusible Link 5 (250A)

T1-2-6
 GENERAL / Component Layout

Used Circuit Fusible Link

Part Name Circuit Connected

Fusible Link 1 Monitor, Back up Power Circuit Fuse Box 1 (#1, #2)
Main Controller B, DLU Main Power Circuit Fuse Box 2 (#1)
ECM Power Circuit
Fusible Link 2 Work Light Relays 1, 2 Power Circuit Fuse Box 2 (#11～14)
Washer Relay, Wiper Relay (L, H1, H2),
Wiper Motor Power Circuit
Air Conditioner Power Circuit
Auto-Lubrication Solenoid Valve Relay, Flow Rate
Decrease Solenoid Valve Relay, Power Transistors 1, 2
and 3
Fusible Link 3 DC-DC Converter Power Circuit Fuse Box 2 (#4～9)
Main Controller A, B Solenoid Power Circuit
Travel Alarm Power Circuit
Monitor, Main Controller A Main Power circuit
Step Light Relay Power Circuit
Air Conditioner
Fusible Link 4 Air Heater Signal Relay Power Circuit Air Heater Signal Relay
Fusible Link 5 Starter Relay Power Circuit Starter Relay 1
Fusible Link 6 Alternator Alternator
Fusible Link 7 Preheat Relay 1 Power Circuit Preheat Relay 1
Fusible Link 8 Preheat Relay 2 Power Circuit Preheat Relay 2

T1-2-7
 GENERAL / Component Layout
ELECTRICAL SYSTEM COMPONENTS (3)

On and Around Engine

11

2 10 12 6 1

T18E-01-02-011
1 - ECM 4- Engine Speed Sensor 2 7- Preheat Relay 10 - Engine Oil Pressure
(Pump) Sensor
2 - Alternator 5 - Coolant Temperature 8- Starter 11 - Suction Manifold
Sensor (Monitor) Temperature Sensor
3 - Engine Speed Sensor 1 6 - Engine Oil Level Sensor 9- Coolant Temperature 12 - Fuel Temperature Sensor
(ECM) Sensor (ECM)

T1-2-8
 GENERAL / Component Layout
ELECTRICAL SYSTEM COMPONENTS (4)

Monitor and Switch Panels Monitor Panel

14 15
1

35
2 34
16
33

32
31
3 17
30 18
4 29 19
5
28 20
6
7 27
8 26
25
9
T183-01-02-013
24 23 22 21

13 10

12
11

T183-01-02-010
36
M183-01-035

1 - Monitor Panel 10 - Air Conditioner Control 19 - *Exhaust Gas Temperature 28 - Preheat Indicator
Panel Indicator
2 - Quick Idle Switch 11 - Auto-Lubrication (ALU) 20 - hydraulic Oil Level 29 - Download Indicator
Timer Switch Indicator
3 - Engine Control Dial 12 - Heavy Lift Switch 21 - Engine Warning Indicator 30 - Overheat Indicator
4 - Auto-Idle Switch 13 - Boom Mode Selection 22 - Coolant Level Indicator 31 - Air Filter Restriction
Switch Indicator
5 - Power Mode Switch 14 - Coolant Temperature 23 - Engine Stop Indicator 32 - Lubrication Mode Indicator
Gauge
6 - Travel Mode Switch 15 - Fuel Gauge Switch 24 - Auto-Lubrication Indicator 33 - Liquid Crystal Display
(LCD)
7 - Work Light Switch 16 - Switch Panel 1 25 - Engine Oil Level Indicator 34 - Auto-Idle Indicator
8 - Wiper/Washer Switch 17 - Fuel Level Indicator 26 - Pump Transmission Oil 35 - Quick-Idle Indicator
Pressure Indicator
9 - Key Switch 18 - Alternator Indicator 27 - Engine Oil Pressure 36 - Step Light Switch
Indicator
NOTE: The Item with mark “*” is not used for the machine equipped with CUMMINS engine.

T1-2-9
 GENERAL / Component Layout
ON AND AROUND PUMPS
1

Pump Device Front

2

10 3

4
6

T183-01-02-006

Solenoid Valves and Related Components 5

11
18 2-Spool EHC Valve
Solenoid Valve 17 12
16
Unit 15
Front
13

14

T183-01-02-007

1 - Main Pump 3 Regulator 6 - Transmission Lubrication 11 - Power Increase Solenoid 15 - Pilot Relief Valve
Oil Pump Valve (ST)
2 - Main Pump 1 Regulator 7 - Pilot Pump 12 - Oil Cooler Fan Control 16 - Power Decrease Solenoid
Solenoid Valve (SF) Valve (SA)
3 - Main Pump 1 8 - Main Pump 2 13 - Pilot Filter 17 - Power Decrease Solenoid
Valve (SB)
4 - Oil Cooler Fan Motor Drive 9 - Main Pump 2 regulator 14 - Flow Rate Decrease 18 - Boom Mode Selection
Pump Solenoid Valve Solenoid Valve (SC)
5 - Pump Transmission Oil 10 - Main Pump 3
Pressure Switch

T1-2-10
 GENERAL / Component Layout
OTHERS
Valves (1) 1
Swing Device 20
2 3

19
9

8 Front
Side
5

7 6 T142-01-02-011

T183-01-02-008
21
Travel Device
Valves (2)
10 11 12

18

22

17

16

13
Valves (1)
15 14
T18E-01-02-002
T183-01-02-012C

1 - Pilot Pressure Sensor 7 - Shuttle Valve 13 - Pump 3 Control Valve 18 - Shuttle Valve
(Travel) (Swing Brake Release) (Bucket Roll-In)
2 - Shuttle Valve 8 - Pilot Pressure Sensor (All) 14 - Shockless Valve 19 - Swing Parking Brake
(Auxiliary Circuit) (Front Operation) Release Valve
3 - Reducing Valve 9 - Shuttle Valve 15 - Shuttle Valve 20 - Swing Relief Valve
(Boom Raise Priority) (Swing Make-Up)
4 - Heavy Lift Solenoid Valve 10 - Shuttle Valve 16 - Shock Reducing Valve 21 - Counterbalance Valve
(For Switching Pump 3
Control Pressure)
5 - Travel Mode Control 11 - Arm Preference Valve 17 - Shuttle Valve 22 - Travel Relief Valve
Solenoid Valve (Pilot Pressure Control)
6 - Brake Release Pressure 12 - Signal Control Valve
Switch Valve

T1-2-11
 GENERAL / Component Layout

Coolant Level Switch

T18E-01-02-012

T1-2-12
 SECTION 2
SYSTEM

CONTENTS
SECTION 1 Control System
Outline ...................................................... T2-1-1
Engine Control .......................................... T2-1-2
Pump Control .......................................... T2-1-12
Valve Control .......................................... T2-1-16
Oil Cooler And Fuel Cooler
Fan Motor Control ................................... T2-1-24
Auto-Lubrication Control ......................... T2-1-26

SECTION 2 Hydraulic System

Outline ...................................................... T2-2-1
Pilot Circuit ............................................... T2-2-2
Main Circuit............................................. T2-2-20
Pump Transmission Oil
Cooling Circuit ...................................... T2-2-48
Oil Cooler Fan Motor Circuit ................... T2-2-48

SECTION 3 Electrical System

Outline ...................................................... T2-3-1
Power Source Circuit ................................ T2-3-2
Bulb Check Circuit .................................... T2-3-3
Engine Start Circuit ................................... T2-3-4
Charging Circuit ........................................ T2-3-6
Accessory Circuit ...................................... T2-3-8
Surge Voltage Prevention Circuit ............ T2-3-10

18ET-2-1
(Blank)

18ET-2-2
 SYSTEM / Control System
OUTLINE

Main controllers (A and B) with built-in microcomputers

and ECM (Engine Control Module) are used for ma-
chine control. The main controllers (A and B) and ECM
process signals from the engine control dial, engine
speed sensors (1 and 2) and various switches, actu-
ating the solenoid valves and electronic governor, and
controlling the engine and pumps.

Engine Control
• Engine Speed Control
• Quick-Idle Control
• Auto-Idle Control
• Low Temperature Start Control
• Engine Diagnosing Control

Pump Control
• SP Mode Control
• E Mode Control
• Pump Flow Rate Control at Slow Engine Speed
• Pump Flow Rate Control at Middle Engine Speed
• Power Decrease Control to Prevent Engine
Overheating
• Power Decrease Control Abnormal Engine Oil
Pressure
• Power Decrease Control Low Coolant Level

Valve Control
• Travel Mode Control
• Heavy Lift Control
• Boom Mode Selection Control
• Oil Cooler Fan Motor Control
• Auto-Lubrication Control

T2-1-1
 SYSTEM / Control System
ENGINE CONTROL

Engine Speed Control

Purpose: Controls engine speed in response to en-
gine control dial rotation.

Operation: The electrical signal in response to the

angle of engine control dial is sent to the
ECM. The ECM drives the electronic gov-
ernor due to the electrical signal and con-
trols the engine speed.

Electronic Governor
Key Switch

ECM

Engine Control Dial

T142-04-03-001

T2-1-2
 SYSTEM / Control System
(Blank)

T2-1-3
 SYSTEM / Control System
Quick-Idle Control
Purpose: Reduces fuel consumption by quickly de-
creasing engine speed. This function will
be effective when the machine waits for a
period of time as when waiting for a dump
truck to be set in a loading position.

Operation: When the quick idle switch on top of the

right control lever is turned on, the main
controller sends an electrical signal to the
ECM.
Consequently, the ECM actuates the
electronic governor to lower the engine
speed.

Quick-Idle Switch
Monitor
Controller

Electronic
ECM Governor

T142-04-03-003

T2-1-4
 SYSTEM / Control System
Auto-Idle Control
Purpose: Reduces engine speed, fuels consump-
tion and noise when all control levers are
neutral and the engine is running at a
speed faster than the auto-idle set speed Auto-Idle
with the auto-idle switch ON. Switch
Swing Brake
Release Shuttle
Valve
NOTE: All pilot system pressure is routed to the
swing brake release shuttle valve.
Pressure
Sensor
Operation: When all control levers are in the neutral Main Con-
position, the pressure sensor in the swing troller A
brake release shuttle valve detects the
pilot pressure. Then, approx. 3 second
after main controller A is notified with the
auto-idle switch ON that pilot pressure at
the pressure sensor is 0.4 MPa (4 kgf/cm2,
57 psi) or lower, main controller sends out
a signal to the ECM, by which the ECM
reduces engine speed down to 1400 min-1. SA SB
Pilot Pump
At the same time, main controller sends
out signals to power decrease solenoid
valves (SA and SB). Then, power de-
Power Decrease
crease solenoid valves (SA and SB) are Solenoid Valve
shifted by the delivered signals so that
pilot pressure oil is routed to regulator
ports PG of main pumps (1, 2, and 3).
Consequently, the pump swash angle is
reduced, causing the pump to reduce the
flow rate. Electronic
Governor
When a control lever is operated and the
pressure sensor detects 0.7 MPa
(7kgf/cm2, 100psi) pressure, main con-
troller stops sending out signals the ECM. T18E-02-01-016
Thereby, engine speed is increased up to Main Pump 3 Main Pump 1
the speed set by the engine control dial. Main Pump 2
Therefore, when engine speed increases
more than 1500 min-1, main controller A
stops sending out signals to power de-
crease solenoid valves (SA and SB) so
that the pump swash angle is increased,
causing the pump flow rate to increase.
(Refer to the Regulator in the COMPO-
NENT OPERATION / Pump Device group
for regulator operation.)

T2-1-5
 SYSTEM / Control System
Low Temperature Start Control
Purpose: Heats the intake air when the atmos- NOTE:
pheric temperature is low (0°C (32°F) or • When the key switch is turned except ON before
lower) in order to make the engine start the preheat is finished (30 seconds before), the
more easily. preheat is finished automatically and the preheat
lamp is also turned OFF.
Operation: • When the key switch is kept ON (for 30 seconds
1. When the key switch is turned ON, current from or longer) after the preheat is finished, the pre-
the battery magnetizes relay 1 via fusible link 1, heat is finished automatically and the preheat
key switch and fuse box 1. lamp is also turned OFF.
2. When temperature at suction manifold is 0°C • If the preheat is required once more, return the
(32°F) or lower with the condition at step 1, bat- key switch to the OFF position. After 5 minutes or
tery the ECM relay magnetizes the preheat signal longer turn the key switch ON again in order to
relay. perform the preheat. (The preheat cannot be
3. When the preheat signal relay is magnetized, performed in 5 minute or longer after the key
current from the battery magnetizes preheat re- switch is turned OFF in order to protect the en-
lays 1, 2 via battery relay1, fusible link 4, the gine.)
preheat signal relay.
4. When preheat relays 1, 2 are magnetized, current
from the battery activates air heaters 1 and 2 re-
spectively via fusible links 7, 8 and preheat relays
1, 2.
5. At the same time at step 4, current from the bat-
tery magnetizes the preheat lamp relay via fusible
link 8, preheat relay 2 and the fuse.
6. When the preheat lamp relay is magnetized, cur-
rent flows through the preheat indicator in the
monitor controller and the preheat indicator is
turned ON.
7. Air heaters 1, 2 are activated for 30 seconds.

T2-1-6
 SYSTEM / Control System

Air Heater 1

Key Switch

Fusible Preheat
Link 7 Relay 1 From Battery

Fusible Fuse Box 2

Link 1 Fuse #1 20A
Battery

Fusible
Link 8 Fuse Box 2
Preheat
Preheat Fuse #3 5A
Signal
Relay 2 Relay
Air Heater 2

Fuse 5A

Preheat Electronic
Indicator Preheat Indi- Governor
cator Relay

Monitor
Controller T18E-02-01-017

T2-1-7
 SYSTEM / Control System
Engine Diagnosing Control
Purpose: Performs when the engine or the related
parts are abnormal, and the engine protec-
tion indicator, engine warning indicator or
engine stop indicator is turned ON.

Operation:
When the key switch is turned ON with fault diag-
nosing switch A ON, the electrical signal from ECM is
sent to the monitor and the fault code is displayed on
the engine fault code display panel.
When pushing fault diagnosing switch B forward or
backward while the fault code is displayed on the
engine fault code display panel, the signal from ECM
is selected and the previous or following fault code is T18E-01-02-006

displayed on the monitor.

(Refer to the Troubleshooting A section, TROU-
BLESHOOTING.)

Fuse Box B
Fuse #3 5A

Engine Protection
Indicator

Engine Warning
Indicator
ECM

Engine Engine
Engine Stop
Diagnostic Diagnostic
Indicator
Switch A Switch B

Protection Lamp
Relay

Monitor Engine Stop

Indicator
Engine Stop Lamp
Relay
CPU

DLU
24V Engine Warning
Indicator

T18E-02-01-018

T2-1-8
 SYSTEM / Control System
(Blank)

T2-1-9
 SYSTEM / Control System
Engine Protection Control
Purpose: Monitors engine operating condition ac- • Reduction in Engine Oil Pressure
cording to input signals delivered from 1. When reduction in engine oil pressure keeps for 5
the coolant temperature sensor, coolant seconds or longer, the engine speed decreases.
level switch, engine oil pressure sensor, 2. At the same time at step 1, ECM turns the protec-
suction manifold temperature sensor and tion lamp on engine fault code display monitor ON
engine speed sensor and reduces engine and sends the signal to DLU.
loads by decreasing pump drive power or 3. After DLU receives the signal, DLU sends the
stops the engine in case any engine signal the monitor and main controller A respec-
trouble is detected. tively.
4. After monitor receives the signal, the stop lamp
• Overheating blinks once. After 5 seconds the engine oil pres-
1. When coolant temperature keeps over 100 °C sure indicator is turned ON and the buzzer rings.
(212 °F) for 5 seconds or longer, the engine 5. After receiving the signal from DLU, main con-
speed decreases. troller A instructs power increase solenoid valve
2. At the same time at step 1, ECM turns the protec- ST so that power increase control is deactivated
tion lamp on engine fault code display monitor ON and only power decrease control by power de-
and sends the signal to DLU. crease solenoid valves (SA and SB) are activated.
3. After DLU receives the signal, DLU sends the (Refer to the Pump Control description pages.)
signal the monitor and main controller A respec- 6. In response to engine oil pressure, the control for
tively. auto-stop performs as following (2 types):
4. After monitor receives the signal, the stop lamp 1 ) After 90 seconds, ECM blinks the stop lamp
blinks once. After 5 seconds, the overheat indi- on engine fault code display monitor. After 30
cator is turned ON and the buzzer rings. seconds, the engine stops automatically.
5. After receiving the signal from DLU, main con- 2 ) The engine stops automatically at once.
troller A instructs power increase solenoid valve
ST so that power increase control is deactivated When the engine stops, only the engine oil pres-
and only power decrease control by power de- sure indicator on monitor is turned ON.
crease solenoid valves (SA and SB) are activated.
(Refer to the Pump Control description pages.)
6. When coolant temperature increases 115°C (239
°F), ECM blinks the stop lamp on engine fault
code display monitor. After 30 seconds, the en-
gine stops automatically. When the engine stops,
only the overheat indicator on monitor is turned
ON.

T2-1-10
 SYSTEM / Control System
(Blank)

T2-1-11
 SYSTEM / Control System
PUMP CONTROL

SP Mode Control
Purpose: Changes the pump flow rate in response
to the engine speed change to utilize en-
gine output effectively when the engine
runs faster than the rated speed. Main
Operation: When engine speed increases over 1550 Controller A
min-1 with the SP mode ON, main con- SP Mode Switch
troller sends out signals to power increase
solenoid valve ST in response to the sig-
nals from engine speed sensor 1. There-
Engine Speed
fore the signals from main controller A to Sensor 1
Power Increase
power increase solenoid valve ST Solenoid Valve ST
changes as engine speed changes.
Power increase solenoid valve ST deliv- Pilot Pump
ers the pilot oil pressure corresponding to
the received signals to main pump regu-
PZ PZ PZ
lator ports PZ, increasing the pump swash
angle in proportion to the delivered pilot
oil pressure. Then, the pump flow rate in-
creases, accelerating actuator speeds Main Pump
and increasing the engine loads. This op- T183-02-01-009
eration continues until engine speed is
reduced to 1550 min-1.
(Refer to the Regulator in the COMPO-
NENT OPERATION / Pump Device group
for regulator operation.)

E Mode Control
Purpose: Reduces pump 3 flow rate when the ma-
chine is engaged in less production work.
Operation: When the E mode switch is ON, main
controller A sends out signals to power
decrease solenoid valve SA, shifting Main Controller A
power decrease solenoid valve SA. Then, E Mode Switch
the pilot oil pressure is delivered to main
pump 3 regulator port PG, reducing the
main pump 3 swash angle so that the Power Decrease
pump 3 flow rate is reduced. Therefore, Solenoid Valve SA
Pilot
actuator operating speeds are reduced. Pump
NOTE: Since no signals are delivered to power
PG
decrease solenoid valve SB from main
controller A, main pumps 1 and 2 are not
controlled.
(Refer to the Regulator in the COMPO-
NENT OPERATION / Pump Device group Main Pump 3
for regulator operation.)
T142-04-03-006

T2-1-12
 SYSTEM / Control System
Pump Flow Rate Control at Slow Engine Speed
Purpose: Prevents the engine from stalling even if
engine speed is reduced to less than 850
min-1 due to engine load increase while
the engine is running at slow speed. Main
Controller A

Operation: When main controller A is instructed by

signals from engine speed sensor 1 that
Signal
engine speed is reduced to less than 850 Control
min-1, main controller A sends out signals Flow Rate Decrease Valve
to the flow rate decrease solenoid valve. Solenoid Valve
When the flow rate decrease solenoid
Engine Speed
valve is activated, it closes the pilot Sensor 1
pressure oil circuit from the pump flow
rate control valve in the signal control
valve to main pump 1 and 2 regulator
ports Pi. Consequently, the pump swash
angle is reduced so that the engine load
is reduced. This operation continues until
engine speed increases to more than
1400 min-1. Main Pump 2 Main Pump 1
(Refer to the COMPONENT OPERATION T18E-02-01-006
/ Signal Control Valve group for signal
pilot control valve operation.)
(Refer to the Regulator in the COMPO-
NENT OPERATION / Pump Device group
for regulator operation.)

T2-1-13
 SYSTEM / Control System
Pump Flow Rate Control at Middle Engine Speed
Purpose: Prevents engine speed from being re-
duced to less than 1400 min-1 due to en-
gine load while the engine is running at
middle speed. Main
Controller A

Operation: When main controller A is instructed by

signals from engine speed sensor 1 that
engine speed is reduced to less than Pilot Pump
1400 min-1, main controller A sends out
signals to power decrease solenoid Power
valves SA and SB. Decrease
Solenoid
When power decrease solenoid valves Valve
SA and SB are shifted, the pilot pressure
SA SB
oil routed to main pump 1, 2, and 3 regu-
lator ports PG. Consequently, the pump
swash angle is reduced so that the pump
flow rate is reduced, reducing the engine
Engine Speed
loads. This operation continues until en- Sensor 1
gine speed increases to more than 1500
min-1.
(Refer to the Regulator in the COMPO-
NENT OPERATION / Pump Device group
PG PG PG
for regulator operation.)

Main Pump

T18E-02-01-007

T2-1-14
 SYSTEM / Control System
Power Decrease Control to Prevent Engine
Overheat
Power Decrease Control at Abnormal Engine Oil
Pressure
Power Decrease Control at Lower Coolant Level Suction Manifold Tem-
Purpose: Reduces main pump 1, 2, and 3 output to perature Sensor ECM
reduce the engine loads when the coolant
Engine Oil Pressure
temperature increases over 100 °C (212 Sensor
°F), when the engine oil pressure is ab-
DLM
normal, when the coolant level is reduced, Coolant Level Switch
or when temperature of suction manifold
reaches over 85 °C (185 °F). Coolant Tempera-
ture Sensor
Main
Operation: When the coolant temperature increases Controller A
Power Decrease
to 100 °C (212 °F), when engine oil Solenoid Valve
pressure is reduced or when temperature SB
of suction manifold reaches over 85 °C Power Decrease
(185 °F) and if the coolant level is re- Solenoid Valve
SB
duced to lower than the specified level,
main controller A sends out signals to
power decrease solenoid valves SA and Pilot Pump
SB, shifting power decrease solenoid
valves SA and SB. Then, the pilot pres-
sure oil is routed to main pump 1, 2, and 3 PG PG PG
regulator ports PG. Consequently, swash
angle in main pumps 1, 2, and 3 is re-
duced so that the pump flow rate is re-
duced. Thereby, the engine loads are Engine
reduced, preventing the engine from be-
ing overloaded.
Main Main Main
Pump 3 Pump 2 Pump 1

T18E-02-01-014

T2-1-15
 SYSTEM / Control System
VALVE CONTROL

Travel Mode Control

Purpose: Controls the travel mode.
Operation: Slow Mode:
When the travel mode switch is turned to
position, main controller B doesn’t
send signals to the travel mode control
solenoid valve so that the solenoid valve
is deactivated. Therefore, reducing valve
port D is connected to the hydraulic oil
tank. Then, pilot oil pressure delivered
from the pilot pump to the travel motors
via the brake release pressure control
valve and the reducing valve is main-
tained at 1.8 MPa (18 kgf/cm2, 256 psi) by
the reducing valve.

Accordingly, the travel mode control

valves in the travel motors are not shifted.
Then, pressure oil from the main pump is
not supplied to the tilt pistons so that the
travel motors rotate at slow speed. (Refer
to the Travel Motor in the COMPONENT
OPERATION / Travel Device group for
travel motor swash angle control opera-
tion.)

T2-1-16
 SYSTEM / Control System

From Main
Pump

Pilot Pump

Reducing From Main

Valve 1.8 MPa Pump
Travel Parking
Port D Shuttle Valve Motor Brake
Brake
Release
Pressure Tilt Pis-
Control ton
Valve
OFF
Travel Mode
Control
Solenoid
Valve Travel
Mode
Control
Valve

Shuttle
Valve

Main Controller B From Signal

Control Valve

Travel
Mode
Switch T183-02-02-013

T2-1-17
 SYSTEM / Control System
Fast Mode:
When the travel mode switch is turned to posi-
tion, main controller B sends out signals to the travel
mode control solenoid valve so that the solenoid valve
is activated. Therefore, pilot oil pressure from the pilot
pump via the brake release pressure control valve and
the travel mode control solenoid valve is routed to re-
ducing valve port D, fully opening the reducing valve.
Then, pilot oil pressure delivered from the pilot pump
to the travel motors is maintained at 3.9 MPa (40
2
kgf/cm , 569 psi).

Accordingly, the travel mode control valves in the

travel motors are shifted. Then, pressure oil from the
main pump is supplied to the tilt pistons so that the
travel motors rotate at fast speed.
(Refer to the Travel Motor in the COMPONENT OP-
ERATION / Travel Device group for travel motor swash
angle control operation.)

T2-1-18
 SYSTEM / Control System

From Main
Pump

Pilot Pump

From Main
Reducing 3.9 MPa Pump
Valve Travel Parking
Port D Shuttle Valve Motor Brake
Brake
Release
Pressure Tilt
Control Piston
Valve

ON Travel
Mode
Control
Solenoid Travel
Valve Mode
Control
Valve

Shuttle
Valve

From Signal Pilot

Main Controller B Control Valve

Travel
Mode
Switch T183-02-02-014

T2-1-19
 SYSTEM / Control System
Heavy Lift Control
Purpose: Increases the main relief set-pressure.

Operation: When the heavy lift switch is turned ON,

main controller A receives signals from
the switch and activates the heavy lift
solenoid valve and activates the flow rate
decrease solenoid valve. Then, the pilot
oil pressure from the pilot pump is routed
to the main relief valve via the heavy lift
solenoid valve, increasing the relief
set-pressure. (refer to the main relief
pressure control on the COMPONENT
OPERATION /Control Valve group.)

Other than the above, the pilot pressure

oil from the pump flow rate control valve
in signal control valve to main pump 1 and
2 regulator ports Pi is blocked by the flow
rate decrease solenoid valve so that main
pump 1 and 2 flow rates are reduced to
minimum.

T2-1-20
 SYSTEM / Control System

Heavy Lift
Switch

Main Control Valve

Main Relief
Valve
Main
Controller A

Signal
Control
Valve

Heavy Lift
Flow Rate Decrease
Solenoid
Solenoid Valve
Valve

Pilot
Pump Pi Pi
REG REG REG

Main Main Main T18E-02-01-012

Pump 3 Pump 2 Pump 1

T2-1-21
 SYSTEM / Control System
Boom Mode Selection Control
Purpose: Reduces machine vibration while per-
forming digging or leveling work.
Operation: When the boom mode selection switch is
turned ON, main controller B activates
boom mode selection solenoid valve SC
so that pressure oil from the pilot pump is
routed to the boom overload relief pres-
sure switch valve via boom mode selec-
tion solenoid valve SC. Then, the boom
overload relief pressure switch valve is
shifted, blocking the pressure oil flow from
the boom cylinder rod side to the overload
relief valve pilot port. Therefore, the
overload relief valve set-pressure is re-
duced to 9.8 MPa (100 kgf/cm2, 1420 psi).
This reduces machine vibration while
performing digging or leveling, but dis-
enables to lower the bucket to raise the
machine front off ground.
NOTE: Refer to the COMPONENT OPERATION /
Control valve group for the boom overload
relief pressure switch valve.

T2-1-22
 SYSTEM / Control System

Boom Cylinder

Boom Mode Selection

Solenoid Valve SC

Pilot Pump

Boom Overload Relief Overload Relief Valve

Pressure Switch Valve
Main
Controller B

Boom Mode
Selection Switch

Travel Front All

Pilot Pressure
Sensors

T18E-02-01-009

T2-1-23
 SYSTEM / Control System
OIL COOLER AND FUEL COOLER FAN
MOTOR CONTROL
Fuel Temperature
Purpose: Changes the fan motor speed in three Sensor
stages (Low, Middle and High speeds) as
the hydraulic oil and fuel temperatures Hydraulic Oil Temperature Sensor
change to properly maintain the hydraulic
Main Controller A
oil and fuel temperatures.

Operation: Main controller A receives signals in re-

Oil Cooler Fan
sponse to each temperature from the hy- Motor
draulic oil temperature sensor and fuel
temperature sensor. Based on the received
signals, controller A activates fan control Oil Cooler
Fan Motor
solenoid valve SF so that pressure oil from Drive Pump
the pilot pump is routed to the fan motor
drive pump, controlling the fan motor drive
pump speed. Then, the oil cooler fan motor
speed is controlled by pressure oil from the
fan motor drive pump. Oil Cooler Fan
Pilot Pump T183-02-01-015
Control Solenoid
Hydraulic Oil Valve SF
Temperature

If the fan motor speed mode of fuel temperature is

different from that of hydraulic oil temperature, the fan
runs in response to the faster fan motor.

-1
1400±50 min
-1 -1
800 min 800 min

-1 -1
1100 min 1100 min

Fan Motor Speed

T18E-02-01-011
Oil Temperature VS Fan Motor Speed

Fuel Temperature Oil Cooler Fan Hydraulic Oil Pilot Pressure from Fan Control Fan Motor
Motor Speed Temperature Solenoid Valve [Current from MC] Speed Mode
66 °C (151 °F) 800→ 70 °C (157 °F) 0.99 Mpa (10 kgf/cm2, 142 psi) Low→Middle
1100 min-1 [285 mA]
69 °C (156 °F) 1100→ 80 °C (176 °F) 0 MPa (0 kgf/cm2, 0 psi) Middle→High
1400±50 min-1 [200 mA]
66 °C (151 °F) 1400±50→ 75 °C (167 °F) 0.99 Mpa (10 kgf/cm2, 142 psi) High→Middle
1100 min-1 [285 mA]
63 °C (145 °F) 1100→ 65 °C (149 °F) 1.36 Mpa (14 kgf/cm2, 199 psi) Middle→ Low
800 min-1 [309 mA]

NOTE: The fan motor speeds shown in the above

table are those driven at engine rated
speed (1650 min-1).

T2-1-24
 SYSTEM / Control System
(Blank)

T2-1-25
 SYSTEM / Control System
AUTO-LUBRICATION CONTROL

Purpose: Automatically lubricates the front attach-

ment joint pins with grease.
(Refer to the COMPONENT OPERATION /
Others (Upperstructure) group.)

Operation:
• Auto-Lubrication • Manual Lubrication
1. When the auto-lubrication switch on the monitor 1. When the auto-lubrication switch on the monitor
panel is turned to the AUTO position, the monitor panel is turned to the MANUAL position, the
controller sends a signal to the main controller B. monitor controller sends a signal to the main con-
2. Then, based on signals from the auto-lubrication troller B.
interval switch, main controller B connects the 2. Then, main controller B connects the ground cir-
ground circuit of the power transistor 3. cuit of the power transistor 3. Power transistor 3
3. As long as a signal from main controller B is input, activates the auto-lubrication relay and holds it
power transistor 3 activates the auto-lubrication activated.
relay. 3. Turn the lubricator grease pump switch ON.
4. As long as the auto-lubrication relay is activated. 4. Since the grease pump discharges grease, lubri-
Then, the grease pump is driven, discharging cation can be performed using the lubricator or a
grease. grease gun.
5. In addition, main controller B monitors the 5. When the proximity switch is turned ON, main
auto-lubrication system with the proximity switch controller B receives a signal, deactivating the
to check if it operates normally. auto-lubrication relay. Therefore, the grease
6. When the proximity switch is turned ON, main pump is stopped.
controller B deactivates the auto-lubrication relay.
Therefore, the grease pump is stopped. NOTE: In manual lubrication mode, the
auto-lubrication indicator is always kept
NOTE: In auto-lubrication mode, if the proximity ON.
switch is not shifted to either ON or OFF
position within 5 minutes after the
auto-lubrication relay is activated, main
controller B judges that a system failure
has occurred or the grease volume has
been reduced, lighting the auto-lubrication
indicator.

T2-1-26
 SYSTEM / Control System

Auto-Lubrication Interval Switch

Power
Transistor 3

Fuse #14

Auto-Lubrication To Lubrication Circuit

Relay

Grease
Pump
Switch
Lubricator

Monitor Controller

Grease
Pump

Auto-Lubrication
Main Proximity Switch
Indicator
Controller B T183-02-01-011

T2-1-27
 SYSTEM / Control System
(Blank)

T2-1-28
 SYSTEM / Hydraulic System
OUTLINE

The hydraulic system consists of the main circuit, pilot

circuit, pump transmission oil cooling circuit, and oil
cooler fan motor circuit.

Pilot Circuit:
A hydraulic circuit that shifts the control valve spools,
that controls the pumps, valves, and motors, and re-
leases the parking brakes.

Main Circuit:
A hydraulic circuit that actuates cylinders, and motors
by pressure oil delivered from the main pumps.

Pump Transmission Oil Cooling Circuit:

An oil circuit that cools the pump transmission oil by
routing it through the oil cooler.

Oil Cooler Fan Motor Circuit:

A hydraulic circuit that drives the oil cooler fan motor
with pressure oil from the oil cooler fan motor drive
pump.
(Refer to the oil cooler fan motor control in Control
System group.)

T2-2-1
 SYSTEM / Hydraulic System
PILOT CIRCUIT

Pressure oil from the pilot pump is used as working

pressure for the following pilot circuits.
• Control Circuit
• Brake Release Circuit
• Travel Motor Overrunning Prevention Circuit
• Main Pump 3 Flow Rate Control Circuit
• Combined Operation Circuit of Arm Roll-Out
(Backhoe) / Arm Retract (Loading Shovel),
Bucket Roll-In (Backhoe) / Tilt-Out (Loading
Shovel), Boom Raise and Swing
• Flow Rate Control Circuit for Boom Raise and
Swing Combined Operation
• Mode Selection Circuit
• Auto-Idle Circuit
• Pump Flow Rate Control Circuit
• Main Relief Set-Pressure Control Circuit
• Boom Raise Priority Circuit
• Travel Mode Control Circuit
• Heavy Lift Circuit
• Boom Mode Selection Circuit

T2-2-2
 SYSTEM / Hydraulic System
Backhoe

Pilot Pilot Valve Pilot Valve

Valve (Arm / Swing) (Boom / Bucket)
(Travel)

Pilot Shut-Off
Valve
Accumul- Shuttle Valve Shuttle Valve Shockless
ator (Pilot Control) (Bucket Roll-In) Valve
Pilot Check Valve

Shuttle Valve (For

Swing Pump 3
Control Pressure)

Pump 2 Pump 1
Regulator Regulator Arm Preference
Valve
Shockless Shuttle Valve
Valve (Swing Parking
Pump 3 Brake Release)
Regulator

Solenoid
Valves
SC SB SA Pump 3
Pilot Relief Control
Valve Valve
Swing Control
2-Unit Shuttle Valve Signal Pressure Control Valve Valve
EHC
Valve (For Swing
Make-Up)
Pilot Filter
Flow Rate
Decrease Main Control Valve
Oil Cooler
Fan Motor Solenoid
Drive Pump Valve
Travel
Motor
Pilot Pump Reducing
Heavy Lift Valve
Solenoid Travel
Valve Motor
Brake Release Travel
Hydraulic Pressure Control
Oil Tank Mode
Valve Solenoid
Valve
Swing
Motor

Swing
Motor

T18E-02-02-001

T2-2-3
 SYSTEM / Hydraulic System
Loading Shovel

Pilot Valve Pilot Pilot Valve Pilot Valve Pilot Valve

(Bucket Close) Valve (Bucket Open) (Arm / Swing) (Boom / Bucket)
(Travel)

Pilot Shut-Off
Valve
Accumul- Shuttle Valve Shuttle Valve
(Pilot Control) Shockless
ator (Bucket Tilt-In) Valve

Pilot Check Valve

Shuttle Valve (For

Swing Pump 3
Control Pressure)
Pump 1
Regulator
Arm Preference
Valve

Pump 2 Shockless
Regulator Valve

Shuttle Valve
(Swing Parking
Pump 3 Pump 3 Brake Release)
Regulator Control
Valve

Solenoid Signal Pressure Control Valve Swing Control

Valves Valve
SC SB SA
2-Unit
Pilot Relief EHC Shuttle Valve
Valve Valve (For Swing
Make-Up)

Oil Cooler
Fan Motor
Pilot Filter Drive Pump

Main Control Valve

Flow Rate
Decrease
Solenoid
Valve Travel
Pilot Pump
Motor
Reducing
Heavy Lift Valve
Solenoid Travel
Valve Motor
Hydraulic
Oil Tank Brake Release Travel
Pressure Control Mode
Valve Solenoid
Valve
Swing
Motor

Swing
Motor

T18E-02-02-002

T2-2-4
 SYSTEM / Hydraulic System
(Blank)

T2-2-5
 SYSTEM / Hydraulic System
Control Circuit
Pressure oil from the pilot pump flows to the main
control valve and to the swing control valve to shift
control valve spools via the pilot check valve, pilot
shut-off valve, pilot valve, shuttle valve, and shock-
less valve.

When the pilot shut-off valve is closed, pressure oil

is not routed to the pilot valve so that the machine
does not operate even if the control levers are oper-
ated. A couple of accumulators are provided in the
control circuit, allowing pressure oil to be delivered
for a while after the engine is stopped. Therefore,
even after the engine stops due to any trouble with
the front attachment raised, pilot oil pressure is de-
livered to the control valve spools so that the front
attachment can be lowered.

T2-2-6
 SYSTEM / Hydraulic System
Backhoe

Swing Boom /
Travel /Arm Bucket

Accumulator

Pilot Shut-Off
Valve
5 6
Pilot Check Valve

Pilot Pump

Signal Control
Valve Hydraulic
Oil Tank 14 13 3 1 10 9 12 11 4 2 8 7

11
10
1 2 12
9
1

5 8
6 8

7
8 1
7
2
2
3 4
1
4

3 3

4
Swing Control Valve
14
13

Main Control Valve

T18E-02-02-003

1- Boom Raise 5- Left Swing 9- Left Travel Forward 12- Right Travel Reverse
2- Boom Lower 6- Right Swing 10- Left Travel Reverse 13- Auxiliary
3- Arm Roll-Out 7- Bucket Roll-In 11- Right Travel Forward 14- Auxiliary
4- Arm Roll-In 8- Bucket Roll-Out

T2-2-7
 SYSTEM / Hydraulic System
Loading Shovel

Swing Boom /
Bucket Close Travel Bucket Open /Arm Bucket
To Pilot Valve
Bucket Open, Close

Accumulator

Pilot Shut-Off
Valve
5 6
Pilot Check Valve

Pilot Pump

Signal Control
Valve Hydraulic
Oil Tank 14 13 3 1 10 9 12 11 4 2 8 7

11
10
1 2 12
9
1

5 8
6 8

7
8 1
7
2
2
3 4
1
4

3 3

4
Swing Control Valve
14
13

Main Control Valve

T18E-02-02-004

1- Boom Raise 5- Left Swing 9- Left Travel Forward 12- Right Travel Reverse
2- Boom Lower 6- Right Swing 10- Left Travel Reverse 13- Bucket Close
3- Arm Retract 7- Bucket Tilt-In 11- Right Travel Forward 14- Bucket Open
4- Arm Extend 8- Bucket Tilt-Out

T2-2-8
 SYSTEM / Hydraulic System
Brake Release Circuit Travel Motor
• When traveling or operating front attachment:
When either the travel or the front attachment con-
trol levers are operated, pressure oil from the signal
control valve is routed to the brake release pressure
control valve. Then, pressure oil from the pilot pump
is routed to the travel motor via the brake release
pressure control valve and the reducing valve, re- Pilot Pump
leasing the travel parking brake.
Also, pressure oil that has passed through the
brake release pressure control valve is routed to the Reducing Valve Shuttle Valve
swing parking brake release valve. Then, pressure
oil from the pilot pump flows through the swing
parking brake release valve and release the swing
parking brake. Therefore, dragging of the swing
brake will be prevented when digging work is per-
formed.

Brake Release
Pressure Control
Valve

Swing Motor Shuttle Valve

From Signal Pilot

Pressure Control Valve

Swing Parking Brake

Release Valve

T18E-02-02-005

Pilot Pump
• When rotating upperstructure:
When the swing lever is operated, swing pilot
pressure oil is routed to the brake release pressure
control valve via the shuttle valves. Then, pressure
oil from the pilot pump flows through the brake re-
lease pressure control valve to the swing parking Brake Release
Swing Parking Pressure
brake release valve pilot port, allowing pressure oil Brake Release Control Valve
from the pilot pump to flow through the swing park- Swing Motor Valve
ing brake release valve to release the swing parking
brake. Shuttle Valve

Shuttle Valve
Swing Pilot
Pressure

T18E-02-02-006

T2-2-9
 SYSTEM / Hydraulic System
Travel Motor Overrunning Prevention Circuit
When the front attachment control levers are oper-
ated, pilot pressure from the front attachment circuit
is routed to the priority valve pilot port in the signal
control valve, shifting the priority valve.
Then, when the right travel lever is operated under
this condition, the pilot pressure oil from the right
travel spool is routed to the flow combiner valve con-
trol spool pilot port in the signal control valve.
Thereby, pressure oil from the pilot pump flows to
the flow combiner valve pilot port in the main control
valve via the priority valve and the flow combiner
valve control spool, shifting the flow combiner valve.
Then, pressure oil from main pump 2 is also routed
into the left travel motor via the flow combiner valve.
Therefore, the flow combiner valve cannot be shifted
unless the right travel lever is operated.
For example, when the left travel/boom combined
operation is operated with the left track jacked-up
using the boom function, only main pump 1 oil flow is
supplied to the left travel motor since the flow com-
biner valve is closed.
(Without this travel motor overrunning prevention cir-
cuit, two main pump flows could be supplied to the
left travel motor, possibly causing overrunning of the
left travel motor in the above mentioned operation.)
(Refer to the COMPONENT OPERATION /Control
Valve group.)

T2-2-10
 SYSTEM / Hydraulic System

Signal Control Valve

Priority Valve
Pilot Pump
Flow Combiner
Valve

Right Travel
(Forward)
Pilot Pressure

Right Travel
(Reverse)
Pilot Pressure

Flow Combiner
Valve Control
Spool

Front Attachment
Pilot Pressure
T18E-02-02-007

T2-2-11
 SYSTEM / Hydraulic System
Main Pump 3 Flow Rate Control Circuit Arm Roll-In
When either function of the arm roll-in (backhoe) / (Backhoe)
Bucket Roll-In
arm extend (loading shovel), bucket roll-in (backhoe) (Backhoe)
Arm Extend
(Loading
/ tilt-in (loading shovel), boom raise or swing is oper- Tilt-In (Loading
Shovel) Pilot
ated, the pump 3 control valve is shifted. Then, pres- Shovel) Pilot
Pressure
Pressure
sure oil from the pilot pump is routed to the main
pump 3 regulator as flow rate control pressure Pi,
increasing the main pump 3 flow rate. Therefore,
actuator operating speeds when a combine opera- Boom Raise Pi-
Shuttle Valve
tion of arm roll-in (backhoe) / arm extend (loading lot Pressure
shovel), bucket roll-in / tilt-in (loading shovel), boom
raise or swing is made are ensured.
(Refer to the COMPONENT OPERATION / Pump Right Swing Pi-
lot Pressure
Control Valve group.)
Left Swing Pilot
Pressure

Shuttle Valve

REG REG REG

Main Main Main

Pump 3 Pump 3 Pump 2 Pump 1
Control
Valve

Pilot Pump
T18E-02-02-008

T2-2-12
 SYSTEM / Hydraulic System
(Blank)

T2-2-13
 SYSTEM / Hydraulic System
Combined Operation Circuit of Arm Roll-Out
(Backhoe) / Arm Retract (Loading Shovel),
Bucket Roll-In (Backhoe) / Tilt-Out (Loading
Shovel), Boom Raise, and Swing
When the arm roll-out (backhoe) / arm retract (load-
ing shovel) and swing functions are operated at the
same time for example, the swing pilot pressure oil
shifts the arm preference valve via the shuttle valves.
Therefore, no pilot pressure oil is routed to the arm 3
spool pilot port in the swing control valve so that arm
3 spool is not moved. Then, the return oil from the
arm cylinder cannot pass through arm 3 spool, re-
stricting the return oil flow. Thereby, arm hesitation
while rolling out (backhoe)/retracting the arm (load-
ing shovel) is prevented.
(Refer to the combined operation circuit in this group
and the COMPONENT OPERATION /Pump Control
Valve group.)

T2-2-14
 SYSTEM / Hydraulic System

NOTE: The drawing shown in the below is Back-

hoe.

Left Swing Right Swing Boom Raise Bucket Roll-In Arm Roll-Out
Pilot Pressure Pilot Pressure Pilot Pressure Pilot Pressure Pilot Pressure Arm Cylinder

Shuttle Valve (Pilot

Pressure Control)

Arm
Preference
Valve

Main Control Valve

Swing Control Valve

Boom 3

Swing

Arm 1
Arm 2
Arm 3
Bucket 3

Main Pump 1

Main Pump 2

Main Pump 3

T18E-02-02-009

T2-2-15
 SYSTEM / Hydraulic System
Mode Selection Circuit
• Refer to the SP Mode and E Mode Control in the
Control System group.

Auto-Idle Circuit
• Refer to the Auto-Idle Control in the Control System
group.

Pump Flow Rate Control Circuit

• Refer to the Pump Flow Rate Control at Slow En-
gine Speed and the Pump Flow Rate Control at
Middle Engine Speed in the Control System group.

Main Relief Set-Pressure Control Circuit

• Refer to the COMPONENT OPERATION / Main Re-
lief Pressure Setting Change in the Control Valve
group, and Heavy Lift Control in the Control System
group.

Boom Raise Priority Circuit

• Refer to the Main Circuit, Combined Control Circuit,
Boom and Arm Combined Operation (Boom Raise
and Arm Roll-Out) in this group.

Travel Mode Control Circuit

• Refer to the Travel Mode Control in the Control Sys-
tem group.

Heavy Lift Circuit

• Refer to the Heavy Lift Control in the Control Sys-
tem group.

Jack-Up Prevention Circuit

• Refer to the Jack-up Prevention Control in the Con-
trol System group.

T2-2-16
 SYSTEM / Hydraulic System
(Blank)

T2-2-17
 SYSTEM / Hydraulic System
Swing Motor Make-Up Circuit

Pressure oil from the pilot valve flows into port Pi

of the regulator in the main pump 2 via the shuttle
valve (for swing makeup) and shockless valve
when the swing operation is operated. Therefore,
the delivery volume from the main pump 2 in-
creases.
When the swing control lever is returned to the
neutral position, pressure oil routed to port Pi of
the regulator in the main pump 2 decreases, so
that the delivery volume from the main pump 2
tries to decrease.
However, the shockless valve prevents the pres-
sure oil from returning suddenly to the hydraulic oil
tank from port Pi of the regulator in the main pump
2. As a result, the delivery volume from the main
pump 2 is maintained for a time being.
As delivery volume from the main pump 2 is main-
tained, back pressure of the return oil from the
main control valve 4-spool side increases, so that
the make-up volume to the swing motor increases.

As a result, the cavitation of the swing motor can be

prevented.

T2-2-18
 SYSTEM / Hydraulic System

Swing (Right) to Swing Control Valve

Pilot Pressure Shuttle Valve
Right Swing
(for Swing Make-Up)

Swing (Left) to Swing Control Valve

Pilot Pressure Left Swing

Shockless Valve

Pi
Main Pump 2 REG

Main Control Valve

4-Spool
Side

Oil Cooler

Swing Motor

5-Spool
Side

T18E-02-02-010

T2-2-19
 SYSTEM / Hydraulic System
MAIN CIRCUIT
Main pumps 1, 2, and 3 draw hydraulic oil from the
hydraulic oil tank. Main pump 1, main pump 2, and
main pump 3 deliver hydraulic oil to the 5-spool sec-
tion of the main control valve, to the 4-spool section of
the main control valve, and the swing control valve,
respectively. The delivered oil is further routed to the
motors and/or cylinders in response to control valve
operation. The return oil from the main control valve
flows back to the hydraulic oil tank through the two
return circuits.
When the return oil temperature is low (high oil vis-
cosity), or when a large amount oil is returned, oil flow
resistance in the oil cooler increases. In this case, the
bypass relief valve opens so that the return oil flows
directly back to the hydraulic oil tank.
When the return oil temperature increases (low oil
viscosity), oil flow resistance in the oil cooler de-
creases. Therefore, the bypass relief valve doesn’t
open so that the return oil flows back to the hydraulic
oil tank after passing through the oil cooler.

T2-2-20
 SYSTEM / Hydraulic System
Backhoe

Boom Arm Bucket

Cylinder Cylinder Cylinder

Swing Motor
Center
Joint

Hydraulic Oil Tank

Swing Control
Valve
Main Control Valve
Boom 3
(4-Spool Section)
Swing
Right Travel
Bucket 3
Bucket 1
Arm 3
Boom 1
Arm 2

Oil Cooler

Main Control Valve

(5-Spool Section)

Left Travel
Bucket 2
Boom 2
Bypass Relief Valve
Arm 1
Auxiliary

Radiator

Center Joint

Main Pump 3
Main Pump 2
Main Pump 1

Left Travel Motor Right Travel Motor

High Pressure Oil

Low Pressure Oil (Suction)

Low Pressure Oil (Return)

Circuit Oil

Pilot Oil
Drain Oil
T18E-02-02-024

T2-2-21
 SYSTEM / Hydraulic System
Loading Shovel Bucket
Level Boom Arm open/close Bucket
Cylinder Cylinder Cylinder Cylinder Cylinder

Swing Motor

Center
Joint

Hydraulic Oil Tank

Swing Control
Valve
Main Control Valve
Boom 3
(4-Spool Section)
Swing
Right Travel
Bucket 3
Bucket 1
Arm 3
Boom 1
Arm 2

Oil Cooler

Main Control Valve

(5-Spool Section)

Left Travel
Bucket 2
Boom 2
Bypass Relief Valve
Arm 1
Bucket
open/close

Radiator

Center Joint

Main Pump 3
Main Pump 2
Main Pump 1

Left Travel Motor Right Travel Motor

High Pressure Oil

Low Pressure Oil (Suction)

Low Pressure Oil (Return)

Circuit Oil

Pilot Oil
Drain Oil
T18E-02-02-025

T2-2-22
 SYSTEM / Hydraulic System
(Blank)

T2-2-23
 SYSTEM / Hydraulic System
Single Operation Circuit
• Boom Operation
Backhoe
Boom Raise:
Pressure oil from main pump 1 flows through the
boom 2 spool in the 5-spool section of the main
control valve. Pressure oil from main pump 2 flows
through the boom 1 spool in the 4-spool section of
the main control valve. Pressure oil from main
pump 1 and 2 merges, and flows to the boom cyl-
inder bottoms after passing through holding valve
check valve. Pressure oil from main pump 3 flows
through the boom 3 spool in the swing control valve
and the holding valve check valve.

Boom Lower:
Pressure oil from the main pump 2 flows is fed to
the boom cylinder rod side through the boom 1
spool in the 4-spool section of the main control
valve. Pressure oil from the main pump 3 flows
back into the hydraulic oil tank through the boom 3
spool in the swing control valve, so that it does not
flow to the boom cylinder rod side even when the
spool is shifted.
The lowering side of the boom 2 spool in the
5-spool section of the main control valve is exclu-
sively used for boom regeneration. Only the return
oil from the boom cylinder bottom side flows there.

NOTE: Refer to the COMPONENT OPERATION /

Control Valve group for the holding valve
functions.

T2-2-24
 SYSTEM / Hydraulic System

Boom Cylinder Boom Cylinder

Swing Control Valve

Main Control Valve 4-Spool Section
Holding Valve
Check Valve
Holding Valve
Switch Valve

Boom 3

Boom1

Boom 2

Holding Valve
Check Valve

5-Spool Section

Main Pump 1
Holding Valve
Main Pump 2 Switch Valve

Main Pump 3

T18E-02-02-012

T2-2-25
 SYSTEM / Hydraulic System

Loading Shovel
Boom Raise:
Pressure oil from main pump 1 flows through the
boom 2 spool in the 5-spool section of the main
control valve. Pressure oil from main pump 2 flows
through the boom 1 spool in the 4-spool section of
the main control valve. Pressure oil from main
pump 1 and 2 merges, and flows to the boom cyl-
inder bottom side and the level cylinder rod side
after passing through holding valve check valve.
Pressure oil from main pump 3 flows through the
boom 3 spool in the swing control valve and the
holding valve check valve.

Boom Lower:
Pressure oil from the main pump 2 flows is fed to
the boom cylinder rod side and the level cylinder
bottom side through the boom 1 spool in the
4-spool section of the main control valve. Pressure
oil from the main pump 3 flows back into the hy-
draulic oil tank through the boom 3 spool in the
swing control valve, so that it does not flow to the
boom cylinder rod side even when the spool is
shifted.
The lowering side of the boom 2 spool in the
5-spool section of the main control valve is exclu-
sively used for boom regeneration. Only the return
oil from the boom cylinder bottom side flows there.

NOTE: Refer to the COMPONENT OPERATION /

Control Valve group for the holding valve
functions.

T2-2-26
 SYSTEM / Hydraulic System

Boom Cylinder Boom Cylinder

Level
Cylinder

Swing Control Valve

Main Control Valve 4-Spool Section
Holding Valve
Check Valve
Holding Valve
Switch Valve

Boom 3

Boom1

Boom 2

Holding Valve
Check Valve

5-Spool Section

Main Pump 1
Holding Valve
Main Pump 2 Switch Valve

Main Pump 3

T18E-02-02-013

T2-2-27
 SYSTEM / Hydraulic System
• Arm Operation
Backhoe
Arm Roll-In:
The return oil from the arm cylinder rod side flows
into the arm 1 spool in the 5-spool side of the main
control valve. The return oil is twice reduced by the
orifices at the arm 1 spool and the arm regenerative Check Valve
valve in order to increase the pressure on the arm
cylinder rod side. When this pressure exceeds that
on the arm cylinder bottom side, the check valve in Arm 1 Spool
the arm 1 spool opens.
The return oil from the arm cylinder rod side com-
bines with that from the main pump 1, and then Orifice
flows again to the arm cylinder bottom side.
Pressure oils from the main pump 2 and main pump
3 flow to the arm cylinder bottom side through the
arm 2 spool in the 4-spool section of the main con-
trol valve and the arm 3 spool of the swing control Arm Re-
valve, respectively. The return oil does not flow generative
through the swing control valve, because it is Valve
blocked by a check valve in the return route to the
Orifice
swing control valve.

Arm Roll-Out:
Pressure oil from main pumps 1 and 2 flows to the
arm cylinder rod side while taking the same oil pas-
sages as those of arm roll-in operation and opening
T111-02-05-035
the holding valve check valve. Pressure oil from
main pump 3 passes through arm 3 spool in the
swing control valve, opens the check valve, and
flows to the arm cylinder rod side.

NOTE: Refer to the COMPONENT OPERATION /

Control Valve group for the holding valve
functions.

T2-2-28
 SYSTEM / Hydraulic System

Arm
Cylinder

Main Control Valve 4-Spool Section

Swing Control Valve

Holding Valve
Check Valve

Arm 3 Arm1
Arm 2

Check
Valve

5-Spool Section

Holding Valve
Switch Valve Main Pump 1

Main Pump 2 Arm Regenerative Valve

Main Pump 3

T18E-02-02-014

T2-2-29
 SYSTEM / Hydraulic System
Loading Shovel
Arm Extend:
The return oil from the arm cylinder rod side flows
into the arm 1 spool in the 5-spool side of the main
control valve. The return oil is twice reduced by the
orifices at the arm 1 spool and the arm regenerative
valve in order to increase the pressure on the arm Check Valve
cylinder rod side. When this pressure exceeds that
on the arm cylinder bottom side, the check valve in
the arm 1 spool opens. Arm 1 Spool
The return oil from the arm cylinder rod side com-
bines with that from the main pump 1, and then
flows again to the arm cylinder bottom side. Orifice
Pressure oils from the main pump 2 and main pump
3 flow to the arm cylinder bottom side through the
arm 2 spool in the 4-spool section of the main con-
trol valve and the arm 3 spool of the swing control
valve, respectively. The return oil does not flow Arm Re-
through the swing control valve, because it is generative
blocked by a check valve in the return route to the Valve
swing control valve.
Orifice

Arm Retract:
Pressure oil from main pumps 1 and 2 flows to the
arm cylinder rod side while taking the same oil pas-
sages as those of arm extend operation and open-
ing the holding valve check valve. Pressure oil from
T111-02-05-035
main pump 3 passes through arm 3 spool in the
swing control valve, opens the check valve, and
flows to the arm cylinder rod side.

NOTE: Refer to the COMPONENT OPERATION /

Control Valve group for the holding valve
functions.

T2-2-30
 SYSTEM / Hydraulic System

Arm
Cylinder

Main Control Valve 4-Spool Section

Swing Control Valve

Holding Valve
Check Valve

Arm 3 Arm1
Arm 2

Check
Valve

5-Spool Section

Holding Valve
Switch Valve Main Pump 1

Main Pump 2 Arm Regenerative Valve

Main Pump 3

T18E-02-02-015

T2-2-31
 SYSTEM / Hydraulic System
• Bucket Operation
Bucket Roll-In (Backhoe) / Tilt-In (Loading Shovel)
Pressure oil from main pump 1, main pump 2, and
main pump 3 flows to the bucket cylinder bottoms
after passing through the bucket 2 spool in the
5-spool section of the main control valve, the
bucket 1 spool in the 4-spool section of the main
control valve, and the bucket 3 spool in the swing
control.

Bucket Roll-Out (Backhoe) / Tilt-Out (Loading

Shovel)
Pressure oil from main pump1 and 2 is routed to
the bucket cylinder rod side after passing through
the bucket 2 spool in the 5-spool section and the
bucket 1 spool in the 4-spool section of the main
control valve, respectively. Pressure oil from main
pump 3 doesn’t flow to the bucket cylinder rod side
because the oil circuit from the bucket 3 spool to
the bucket cylinder is blocked.

T2-2-32
 SYSTEM / Hydraulic System

NOTE: The drawing shown in the below is

Backhoe.
Bucket
Cylinder

Main Control Valve 4-Spool Section

Swing Control Valve

Bucket 1

Bucket 2

Bucket 3

5-Spool Section

Main Pump 1

Main Pump 2

Main Pump 3

T18E-02-02-016

T2-2-33
 SYSTEM / Hydraulic System
• Bucket Open/Close Operation (Loading Shovel
only)
Bucket Open:
Pressure oil from main pump 1 flows to the bucket
open/close cylinder rod side after passing through
the bucket open/close spool in the 5-spool section
of the main control valve.

Bucket Close:
Pressure oil from main pump1 flows to the bucket
open/close cylinder bottom side after passing
through the bucket open/close spool in the 5-spool
section.

T2-2-34
SYSTEM / Hydraulic System

Bucket Open/close
Cylinder

Main Control Valve 4-Spool Section

5-Spool Section

Backet
Open/Close

Main Pump 1

T18E-02-02-017

T2-2-35
 SYSTEM / Hydraulic System
• Travel Operation
Left Travel:
Pressure oil from main pump 1 is routed into the left
travel motor via the left travel spool in the 5-spool
section of the main control valve.

Right Travel:
Pressure oil from main pump 2 is routed into the
right travel motor via the right travel spool in the
4-spool section of the main control valve.

• Swing Operation
Pressure oil from main pump 3 is routed into the
swing motor via the swing spool in the swing control
valve.

T2-2-36
 SYSTEM / Hydraulic System

NOTE: The drawing shown in the below is Backhoe.

Left Right
Travel Travel
Motor Motor

Main Control Valve 4-Spool Section

Swing Control Valve

Swing

Swing Motor 5-Spool Section

Main Pump 1

Main Pump 2

Main Pump 3

T18E-02-02-018

T2-2-37
 SYSTEM / Hydraulic System
Combined Operations
• Swing and Boom Combined Operation
When swing and boom raise combine operation is
performed, the swing and boom 1, 2, and 3 spools
are shifted. Pressure oil from main pump 1 is
routed to the boom 2 spool after passing through
the auxiliary and boom 2 spools in the 5-spool sec-
tion of the main control valve. Pressure oil from
main pump 2 is routed to the boom 1 spool via the
parallel circuit after passing through the right travel
spool in the 4-spool section of the main control
valve. Then, both pressure oils are jointly routed to
the bottom of boom cylinders via the holding valve
check valve. Pressure oil from main pump 3 enters
the swing control valve. Then, it is separately
routed to the boom 3 spool and the swing spool.
Pressure oil from the boom 3 spool is routed to the
boom cylinder bottoms via the holding valve check
valve. Pressure oil from the swing spool is routed to
the swing motor via the parallel circuit.

For simultaneous operation of swing and boom low-

ering, the pressure oil from the main pump 2 flows
to the boom cylinder rod side through the travel
(right) spool in the main control valve and the
parallel circuit. The pressure oil from the boom 3
spool in the swing control valve does not flow into
the hydraulic oil tank, because it is blocked by the
swing spool. The pressure oil from the main pump
3 flows into the swing spool through the parallel cir-
cuit.
The return oil from the boom cylinder flows back
into the hydraulic oil tank through the boom 1 spool
and boom 2 spool.

T2-2-38
 SYSTEM / Hydraulic System

NOTE: The drawing shown in the below is Back-

hoe.

Boom Cylinder Boom Cylinder

Right
Travel
Swing Control Valve
Main Control Valve 4-Spool Section
Holding Valve Parallel
Check Valve Circuit Parallel Circuit
Holding Valve
Switch Valve

Boom 3

Swing

Boom 1

Boom 2

Arm 1

Holding Valve
Auxiliary Check Valve

Swing Motor
5-Spool Section

Main Pump 1
Holding Valve
Main Pump 2 Switch Valve

Main Pump 3

T18E-02-02-019

T2-2-39
 SYSTEM / Hydraulic System
• Swing and Arm Combined Operation
When swing and arm combined operation is per-
formed, the swing spool and arm spools 1, 2, and 3
are shifted. Pressure oil from main pump 1 is
routed to arm 1 spool via the auxiliary spool in the
5-spool section of the main control valve. Pressure
oil from main pump 2 is routed to arm 2 spool via
the parallel circuit in the 4-spool section of the main
control valve. Then, both pressure oil flows are
jointly routed to the arm cylinder.

Pressure oil from main pump 3 enters the swing

control valve and pressure oil flows to the swing
spool and arm spool 3.
When swing and arm roll-out (backhoe) / arm re-
tract (loading shovel) combined operation is per-
formed, the arm 3 spool in the swing control valve is
not shifted as pilot pressure oil to the arm 3 spool is
blocked by the arm preference valve. Then, the re-
turn oil from the arm cylinder cannot pass through
arm 3 spool, restricting the return oil flow. Thereby,
arm hesitation while rolling out (backhoe) / retract-
ing the arm (loading shovel) is prevented. When
swing, boom raise, and/or bucket function is oper-
ated, the arm preference valve is shifted, blocking
the pilot pressure oil flow to the arm roll-out (back-
hoe) / arm retract (loading shovel) spool.
(Refer to T2-2-15.)

T2-2-40
 SYSTEM / Hydraulic System

NOTE: The drawing shown in the below is Swing

and Arm Roll-In (Backhoe) Combined.

Arm
Cylinder

Parallel Circuit

Swing Control Valve Main Control Valve 4-Spool Section

Parallel Circuit

Swing

Arm 2
Arm 3 Arm 1

Auxiliary

Swing
Motor
Arm
Preference
Valve 5-Spool Section

Main Pump 1

Main Pump 2

Main Pump 3

T18E-02-02-020

T2-2-41
 SYSTEM / Hydraulic System
• Boom and Arm Combined Operation
Boom Lower and Arm Roll-In (Backhoe) / Arm Ex-
tend (Loading Shovel):
When boom lower and arm roll-in (backhoe) / arm
extend (loading shovel) combine operation is made,
both boom 1, 2, 3 spools and arm 1, 2, 3 spools are
operated.
Pressure oil from main pump 1 is routed to the arm
spool 1 via the auxiliary spool in the 5-spool section
of the main control valve. Pressure oil from main
pump 2 is routed to the boom 1 spool and the arm 2
spool via the parallel circuit in the 4-spool section of
the main control valve.
When pressure in the bottom of the boom cylinder
is higher than pressure in the boom cylinder rod
side, pressure oil in the bottom of the boom cylinder
flows into the boom cylinder rod sides via the boom
2 spool, accelerating the boom lower speed.
Pressure oil from main pump 3 is routed to the arm
3 spool in the swing control valve. Both pressure oil
from the boom 1 spool and the boom 2 spool are
jointly routed into the boom cylinder rod side.

Pressure oil from the arm 1, 2, and 3 spools are

jointly routed into the arm cylinder bottom side.
The holding valve switch valves in the boom 1 and
boom 3 raise circuits are shifted by the boom lower
pilot pressure so that the holding valve check valve
is opened.
The return oil from the boom cylinders flows back to
the hydraulic oil tank through the holding check
valve and the boom 1 and 3 spools.
The holding valve switch valves in the arm 1 roll-out
(backhoe) / retract (loading shovel) circuit are
shifted by the arm roll-out (backhoe) / retract (load-
ing shovel) pilot pressure so that the holding valve
check valve is opened.
The return oil from the arm cylinder is routed to the
arm 1 spool via the holding check valve. The return
oil flow from the arm cylinder is restricted by the ori-
fice in the spool and the arm oil flow regenerative
control valve. When the return oil pressure in-
creases more than the bottom side pressure the
return oil doesn’t flow back to the hydraulic oil tank
but is routed to the arm cylinder bottom through the
arm 1 spool check valve.
(Refer to the COMPONENT OPERATION/Control
Valve group for the boom and arm holding valve
and the arm regenerative valve.)

T2-2-42
 SYSTEM / Hydraulic System

NOTE: The drawing shown in the below is Boom

Lower and Arm Roll-In (Backhoe) Com-
bined.

Boom Cylinder Arm Boom Cylinder

Cylinder

Parallel
Circuit

Swing Control Valve

Main Control Valve 4-Spool Section
Holding Valve
Holding Valve Check Valve
Check Valve

Boom 3

Boom 1
Boom 2

Arm 1
Arm 3
Holding Valve
Check Valve Arm 2

Holding Valve
Auxiliary Check Valve

5-Spool Section

Holding Valve
Holding Valve Main Pump 1 Switch Valve
Switch Valve Arm Regenerative
Main Pump 2 Valve

Main Pump 3

T18E-02-02-021

T2-2-43
 SYSTEM / Hydraulic System
• Boom Raise and Arm Roll-Out (Backhoe) / Arm Re-
tract (Loading Shovel):
When boom raise and arm roll-out (backhoe) / arm
retract (loading shovel) combined operation is made,
both boom 1, 2, 3 spools and arm 1 spool are oper-
ated.
Arm 2 spool is not shifted as pilot pressure oil from
the arm flow rate control valve in the signal control
valve acts on the arm roll-in (Backhoe)/arm extend
(Loading shovel) side of arm 2 spool.
Pressure oil from main pump 1 is routed to the
boom 2 spool via the parallel circuit and the arm 1
spool via the auxiliary spool in the 5-spool section
of the main control valve.
Pressure oil from main pump 2 is routed to the
boom 1 spool via the parallel circuit in the 4-spool
section of the main control valve.
Pressure oil from main pump 3 is routed to the
boom 3 spool in the swing control valve. Pressure
oil is not routed to the arm 3 spool since the parallel
circuit is not provided. Therefore, the boom raise
speed is ensured.
When boom raise and arm roll-out (backhoe) / arm
retract (loading shovel) combined operation is per-
formed, the arm 3 spool is not shifted as pilot pres-
sure oil to arm 3 spool is blocked by the arm pref-
erence valve. Then, the return oil from the arm cyl-
inder cannot pass through arm 3 spool, restricting
the return oil flow. Thereby, arm hesitation while
rolling out (backhoe) / retracting the arm (loading
shovel) is prevented. When swing, boom raise,
and/or bucket function is operated, the arm prefer-
ence valve is shifted, blocking the pilot pressure oil
flow to the arm roll-out (backhoe) / arm retract
(loading shovel) spool.
(Refer to the arm roll-out (backhoe) / arm retract
(loading shovel) and bucket roll-in (tilt-in), boom
raise, swing combined operation circuit.)
Pressure oil from the boom 1 spool, the boom 2
spool, and the boom 3 spool is routed jointly to the
boom cylinder bottoms after passing through the
holding valve check valves. Pressure oil from the
arm 1 spool and the arm 2 spool are jointly routed
to the arm cylinder rod side after passing through
the holding valve check valve.

T2-2-44
 SYSTEM / Hydraulic System
Arm Cylinder

Boom Cylinder

Swing Control Valve

Holding Valve Main Control Valve

4-Spool Section
Check Valve

Boom 3

Boom 1

Boom 2
Arm 2
Arm 1
Holding
Arm 3 Valve
Check Holding Valve
Valve Check Valve

Auxiliary
5-Spool Section
Arm
Preference Main Pump 1 Parallel
Boom Raise
Valve Circuit
Pilot Main Pump 2
Pressure
Main Pump 3

Parallel
Arm Roll-Out Circuit
Pilot
Pressure

Arm Flow Rate Signal Control Valve

Control Valve

NOTE: The drawing shown in the

above is Boom Raise and
Arm Roll-Out (Backhoe)
Combined.

T18E-02-02-022
Arm Roll-out (Backhoe)
Boom Raise Pilot
Arm retract (Loading shovel)
Pressure
Pilot Pressure

T2-2-45
 SYSTEM / Hydraulic System
• Travel and Front Attachment Combined Operation
When travel and front attachment such as boom
raise combined operation is made, the travel spools
(right and left) and boom 1,2,3 spools are operated.
As the boom spools are moved, the signal pilot
pressure increases so that the flow combiner valve
in the main control valve is shifted. Pressure oil
from main pump 1 is routed to the boom 2 spool via
the auxiliary and arm 1 spools in the 5-spool section
of the main control valve.

Pressure oil from main pump 2 is routed into the

right travel motor via the right travel spool in the
4-spool section of the main control valve. On the
other hand, pressure oil is routed into the left travel
motor via the flow combiner valve, the left travel
spool so that the machine can travel straight.
Pressure oil from main pump 3 is routed to the
boom 3 spool in the swing control valve. Pressure
oil from boom 2 and 3 spools are jointly routed to
the boom cylinder bottoms.

T2-2-46
 SYSTEM / Hydraulic System

NOTE: The drawing shown in the below is Backhoe.

Boom Cylinder Boom Cylinder

Left Right
Travel Travel
Motor Flow Combiner Valve Motor

Right 4-Spool
Main Control Valve Travel Section
Swing Control Valve

Boom 3 Left
Travel

Boom 2
Boom1

Arm 1

Auxiliary

5-Spool Section

Main Pump 1

Main Pump 2

Main Pump 3

T18E-02-02-023

T2-2-47
 SYSTEM / Hydraulic System
PUMP TRANSMISSION OIL COOLING
CIRCUIT

The pump transmission oil pump draws transmission

oil and delivers it to the oil cooler. After being cooled in
the oil cooler, the transmission oil is returned into the
pump transmission via each lubricating section.
Thereby, oil temperature increase is prevented, for-
eign matter is filtered and removed, and each part in
the pump transmission is lubricated.

OIL COOLER FAN MOTOR CIRCUIT

Refer to the CONTROL SYSTEM Section.

Manifold

Oil Cooler

Engine

Pump
Transmission

Suction Filter Transmission Oil

Filter Pump
T183-02-02-022

T2-2-48
 SYSTEM / Electrical System
OUTLINE

The electrical system roughly falls into three sections

such as the main circuit, the control circuit, and the
monitor circuits.

• Main Circuit
Engine and accessory circuit

• Control Circuit
Engine and pump control circuits consisting of ac-
tuators such as solenoid valves, main controller A
and B, ECM (Engine Control Module), sensors,
pressure switches, etc.

• Monitor Circuit
Machine operation status indication circuit consist-
ing of sensors, switches, etc.

Outline of the major functions and construction of the

main circuit are explained hereafter.

• Power Source Circuit

Supplies electric power to all electrical systems on
the machine.

• Bulb Check Circuit

Checks for burned monitor warning lights and indi-
cator bulbs.

• Engine Start Circuit

Rotates the starter to start the engine.

• Charging Circuit
Recharges the batteries and supplies current to all
the electrical components from the alternator.

• Accessory Circuit
Operates when the key switch is in the ACC posi-
tion.

• Surge Voltage Prevention Circuit

Protects the electrical equipment such as the con-
troller from surge voltage developed when stopping
the engine.

T2-3-1
 SYSTEM / Electrical System
POWER SOURCE CIRCUIT

Negative terminal of the battery is connected to the

vehicle frame. When the key switch is OFF, battery
current is supplied to the monitor, main controller B,
DLU and ECM as backup power.

Fuse Box 1 Key Switch

DLU

Fusible Link

Battery
Relay 2

Fuse Box 2
Load Damp
Relay Battery
Relay 1

Battery

Monitor
Controller

ECM
Main
Controller B

T18E-02-03-007

T2-3-2
 SYSTEM / Electrical System
BULB CHECK CIRCUIT

When the key switch is turned ON, terminal B is con-

nected to terminals ACC and M in the key switch. The
current from terminal M magnetizes battery relay 2 so
that battery current is routed to the monitor controller
via battery relay 2, the 1 pole junction, and the fuse
box 1, turning all warning lights and indicators on the
monitor panel ON.
Any warning light and/or indicator which doesn’t come
ON at this time may have burned out.

Fuse Box 1 Key Switch

Fusible Link

1 Pole
Junction
Battery
Relay 2

Engine Stop
Solenoid Relay
Battery
Relay 1
Battery

Monitor T18E-02-03-008
Controller

T2-3-3
 SYSTEM / Electrical System
ENGINE START CIRCUIT

1. When the key switch is turned ON, current from 9. Current from the alternator terminal R is applied
key switch terminal M magnetizes battery relays to starter relay 2 terminal R to demagnetize
1 and 2 via fuse #10 in fuse box 1. starter relay 2.
2. When battery relays 1 and 2 are magnetized, 10. Consequently, starter relay 2 is turned OFF so
battery current is routed to starter motors (2 that starter relay 1 magnetizing current is cut off,
used) terminals B via battery relays 1 and 2. turning starter relay 1 OFF.
3. When the key switch is set to the START position, 11. When magnetizing current routed to starter motor
current from key switch terminal G2 is applied terminal C from the starter relay 1 is cut off, the
through fuse #19 in fuse box 1 in order to mag- main contactor is turned OFF, causing the pinion
netize starter relay 1. gear in the starter to retract.
4. When starter relay 1 is magnetized, battery cur- 12. At the same time, battery current is cut off so that
rent is routed to terminal S in starter relay 2 via starter motor stops rotating.
battery relay 2, fusible link 5 and starter relay 1. 13. While the engine is rotating (when the alternator
5. When current is routed to terminal S in starter is generating), no current is routed to starter ter-
relay 2, the coil in starter relay 2 is magnetized minal C. Therefore, even if the key switch is
and terminal B is connected to terminal C. turned to the START position, the starter will not
6. When terminal B is terminal C in the starter motor, rotate.
the coil in the starter motor is magnetized, draw-
ing main contactor so that the contact point is
closed. At the same time, the pinion gear is ex-
tended to engage with the engine ring gear.
7. When the main contactor contact point is closed,
battery current is routed to the motor from starter
motor terminal B, rotating the motor.
8. Once the engine starts, the alternator begins to
generate electricity and supplies current from al-
ternator terminals B and R.

T2-3-4
 SYSTEM / Electrical System

Key Switch

Fusible Link 1
Fuse Battery
1 Pole
Box 1 Relay 2
Junction
Fusible Link 5

Fusible
Link 6

Fusible
Link 7 Battery
Relay 1
Fusible
Link 8
Battery

Fuse
Box 2 Alternator

Starter Relay

Safety Relay 2
Starter Motor 2

Safety Relay 1
Starter Motor 1
ECM

T18E-02-03-010

T2-3-5
 SYSTEM / Electrical System
CHARGING CIRCUIT (KEY SWITCH: ON)
When the key switch is released after the engine Current from alternator terminal B is routed to the
starts, the key switch returns to the ON position. In the batteries via fusible link #6 (100 A) and the battery re-
ON position, key switch terminal B is connected to lay, recharging the batteries. At the same time, current
terminals ACC and M in the key switch. After the en- from alternator terminal B flows to all electrical circuits
gine starts, the alternator is rotated, starting genera- via the junction box, fusible link, fuse box 1, and fuse
tion. box 2. Current from alternator terminal R is routed to
the monitor controller turning the alternator indicator
OFF.

Connection in Fusible Link

Fusible Link Connecting Fuse Box Connected to: Remarks
#1 Fuse Box 1 #1 Monitor (Backup), DLU Backup Power,
(45 A) Main Power
#2 Main Controller B Main Power
Fuse Box 2 #1 ECM Main Power
#2 Fuse Box 1 #11 Work Light Relays 1 and 2 Power
(75 A) #12 Washer Relay, Wiper Relay (L, H1, H2), Power
Wiper Motor
#13 Air Conditioner Power
#14 Auto-Lubrication Solenoid Valve Relay, Power
Flow Rate Decrease Solenoid Valve Relay,
Power Transistors 1, 2 and 3
#3 Fuse Box 1 #4 DC-DC Converter Power
(75 A) #5 Main Controllers A and B Solenoid
Power
#6 Travel Alarm Power
#7 Monitor (Input Power), Main Controller A Main Power
#8 Step Light Relay
#9 Air Conditioner Power
#4 − Preheat Signal Relay Power
(45 A)
#5 − Starter Relay 1 Power
(250 A)
#6 − Alternator Power
(100 A)
#7 − Preheat Relay 1 Power
(125 A)
#8 − Preheat Relay 2 Power
(125 A)

T2-3-6
 SYSTEM / Electrical System

Key Switch

Fusible Link 1

1 pole Battery Relay 2

Fuse Box 1 Fusible Link 2 Junction

Fusible Link 3

Fusible Link 4

Battery Relay 1

Fusible Link 5
Battery
Fusible
Link 6

Fusible
Fuse Box 2 Link 7 Alternator

Fusible Link 8

Starter Relay

Air Heater 2
Air Heater 1

Monitor
Controller

T18E-02-03-011

T2-3-7
 SYSTEM / Electrical System
ACCESSORY CIRCUIT

When the key switch is turned to the ACC position,

terminal B is connected to terminal ACC in the key
switch. Current from terminal ACC is routed to the ra-
dio, cigar lighter, cab light, and horn via fuses #15,
#16, #17 and #18.

Fuse
Box 1 Key Switch
Fusible
Radio
Link #1
Cigar
Lighter
Cab
Light
Horn

Battery Relay 2

Battery Relay 1

Battery

T18E-02-03-009

T2-3-8
 SYSTEM / Electrical System
(Blank)

T2-3-9
 SYSTEM / Electrical System
SURGE VOLTAGE PREVENTION CIRCUIT

The surge voltage prevention circuit prevents the oc-

currence of surge voltage developed when the engine
is stopped to protect electronic components such as
the main controller from being damaged by this surge
voltage. When the key switch is turned OFF while the
engine is running, current from key switch terminal M
to the battery relay is interrupted, deactivating the bat-
tery relay.

The engine, however, will continue running for a while

due to its inertia soon after the key switch is turned
OFF. Consequently, if the battery relay is turned OFF
at this time, current from alternator terminal B cannot
flow to the batteries, casing surge voltage to develop
in the circuit. Battery current is constantly routed to
main controller B. To keep the battery relay ON while
the engine is running, the main controller B built in
timer allows the ground circuit of power transistor 3 to
close for 15 seconds after the key switch is turned
OFF. Therefore, the load damp relay is kept ON for 15
seconds so that current to magnetize the battery relay
is kept supplied. Consequently, current from alternator
terminal B is routed to the batteries via the battery re-
lay, preventing the occurrence of surge voltage.

T2-3-10
 SYSTEM / Electrical System

Key Switch

Fuse
Box 1
Fusible link 1
1 Pole
Junction Battery Relay 2

Fusible link 3

Battery Relay 1

Load Fusible link 5

Damp Battery
Relay Fusible
link 6
Power
Transistor 3 Fusible
link 7 Alternator

Fusible link 8

Main
Controller B

Monitor
Controller
Safety Relay 2

Safety Relay 1

T18E-02-03-012

T2-3-11
 SYSTEM / Electrical System
(Blank)

T2-3-12
 SECTION 3
COMPONENT OPERATION

CONTENTS
Group 1 Pump Device Group 5 Travel Device
Outline ...................................................... T3-1-1 Outline ......................................................T3-5-1
Main Pump, Oil Cooler Fan Motor Travel Reduction Gear ..............................T3-5-2
Drive Pump ............................................. T3-1-2 Travel Motor ..............................................T3-5-3
Regulators ................................................ T3-1-5 Travel Brake Valve ....................................T3-5-5
3-Unit Pump............................................ T3-1-26 Travel Motor Displacement
Angle Change........................................T3-5-10
Group 2 Swing Device Parking Brake .........................................T3-5-12
Outline ...................................................... T3-2-1
Swing Motor.............................................. T3-2-2 Group 6 Signal Control Valve
Valve Unit ................................................. T3-2-4 Outline ......................................................T3-6-1
Swing Parking Brake................................. T3-2-6 Pilot Port ...................................................T3-6-2
Swing Reduction Gear .............................. T3-2-7 Shuttle Valve .............................................T3-6-6
Shockless Valve ......................................T3-6-10
Group 3 Control Valve Pump 1 and 2 Flow Rate Control Valve ...T3-6-14
Outline ...................................................... T3-3-1 Arm Flow Rate Control Valve,
Hydraulic Circuit ..................................... T3-3-10 Flow Combiner Valve Control Spool,
Flow Combiner Valve .............................. T3-3-12 Priority Valve .........................................T3-6-16
Main Relief Valve .................................... T3-3-14
Overload Relief Valve ............................. T3-3-15 Group 7 Other (Upperstructure)
Make-Up Valve........................................ T3-3-15 Pilot Shut-Off Valve ...................................T3-7-1
Holding Valve .......................................... T3-3-16 Shockless Valve ........................................T3-7-2
Arm Regenerative Valve ......................... T3-3-18 Solenoid Valve ..........................................T3-7-6
Boom Overload Relief Pressure Oil Cooler Fan Motor .................................T3-7-8
Switch Valve.......................................... T3-3-20 Accumulator ..............................................T3-7-9
Auto-Lubrication System .........................T3-7-10
Group 4 Pilot Valve
Outline ...................................................... T3-4-1 Group 8 Other (Undercarriage)
Operation .................................................. T3-4-2 Swing Bearing ...........................................T3-8-1
Center Joint...............................................T3-8-2
Track Adjuster ...........................................T3-8-3

18ET-3-1
(Blank)

18ET-3-2
 COMPONENTS OPERATION / Pump Device
OUTLINE
The pump device consists of the pump transmission, The 2nd pump is a pilot pump supplying pressure oil
main pumps and 3-unit pump. Power from the engine to the pilot circuit. The 3rd (farthest away from the
is transmitted to each pump through the pump trans- pump transmission) is a transmission oil circulation
mission. The gear reduction ratio for the main pumps pump.
is 1.083 and for the 3-unit pump is 1.106. The oil cooler fan motor drive pump is a variable dis-
The main hydraulic pump is a variable displacement placement swash plate plunger type pump.
swash plate tandem plunger type pump, supplying The pilot pump and the transmission oil circulation
high pressure hydraulic oil to the main circuit. pump are gear pumps.
The 3-unit pump consists of three pumps of various
types. From the pump transmission side, the 1st
pump is the oil cooler fan motor drive pump.

Main Pump 3

Pump
Transmission

Main Pump 2

Main Pump 1

3-Unit Pump

T183-01-02-006

T3-1-1
 COMPONENTS OPERATION / Pump Device
MAIN PUMP, OIL COOLER FAN MOTOR
DRIVE PUMP
The shaft is connected to the cylinder block via a
spline coupling. The plungers are inserted into the
cylinder block bores.
Engine driving force is transmitted to the shaft via the
pump transmission. As the shaft rotates, the plunger
rotates align with cylinder block, sliding along the sur-
face of the shoe plate. Because the swash plate is
positioned at an angle against the plungers, the
plungers reciprocate in the cylinder block bores,
drawing and discharging hydraulic oil.

Shaft Shoe Plate Servo Piston

Swash Plate Plunger Cylinder Block

W142-02-03-010

T3-1-2
 COMPONENTS OPERATION / Pump Device
Flow Rate Increasing/Decreasing Operation

The flow rate of the pump is varied by changing the

angle of the swash plate which changes the stroke of
the plunger. When pressure oil from the regulator
moves the servo piston, the swash angle changes
accordingly as the swash plate is connected to the
servo piston.

Servo Piston

Shaft

Valve Plate

Cylinder Block

Plunger

Swash Plate
T142-02-01-001C

T3-1-3
 COMPONENTS OPERATION / Pump Device
(Blank)

T3-1-4
 COMPONENTS OPERATION / Pump Device
REGULATORS
The regulators are located on the main pump and oil • Horsepower Reducing Control (only for Main
cooler fan motor drive pump to control the flow rate. Pump)
When the E mode switch is turned ON, the
Regulator Controls horsepower reducing control pressure PG, from
• Constant Torque Control the horsepower reducing solenoid valve SA, acts
Control the pump flow rate depending on the on the main pump 3, and reduces the pump
pump delivery pressure in order to maximize swash angle.
utilization of the engine horsepower. The control When the engine speed slows to 1400 min -1 or
includes the following two operations: less, the horsepower reducing control pressure
(1) Overload Prevention Operation: PG, from the horsepower reducing solenoid
When the delivery pressure increases, reduce valves SA/SB, acts on all main pumps, and re-
the flow rate by reducing the pump swash angle. duce the pump horsepower by reducing the
(2) Flow Rate Recovery Operation: pump swash angle.
When the delivery pressure decreases, increase • Horsepower Increasing Control (only for Main
the flow rate by increasing the pump swash an- Pump)
gle. When the engine speed increases to 1550 min-1
• Flow Rate Control or more, the horsepower increasing control
On the regulator for the main pump, flow rate pressure PZ, from the horsepower increasing
controls pressure Pi from the signal control valve solenoid valve ST, increases the pump horse-
controls the pump swash angle. Consequently, power by increasing the pump swash angle.
the pump delivers the flow rate according to the • Smaller Swash Angle (Less Flow Rate) Priority
lever operation, reducing the fuel consumption. Control
On the regulator for the oil cooler fan motor drive It two or more orders to increase/decrease the
pump, flow rate control pressure Pi from the fan pump flow rate are given simultaneously to the
pump solenoid valve SF controls the flow rate by regulator, the one to indicate the smallest pump
changing the pump swash angle. flow rate will have the higher priority.

Position of Ports
Main Pump Oil Cooler Fan Motor Drive Pump
Pi

Pi

PZ

Psv
PG

T183-03-01-101

P- Pump Delivery Pressure Pi- Flow Rate Control Pressure (Flow Rate Reducing Solenoid
Valve, Signal Control Valve)
PG- Horsepower Reducing Control Pressure (Horsepower Reduc- Psv- Pump Servo Assisting Pressure (Pilot Pump)
ing Solenoid Valve SA, SB)
PZ- Horsepower Increasing Control Pressure (Horsepower In-
creasing Solenoid Valve)

T3-1-5
 COMPONENTS OPERATION / Pump Device
Cross Section (Regulator for Main Pump)

B T183-03-01-002
A

Cross Section A-A

1 2 3 4 5 6 7 8 9 10 11

Pi

14 13 12

T117-02-01-006C
1- Inner Spring 5- Pin 9 - Pin 12 - Feedback Lever
2- Sleeve 6- Pin 10 - Pilot Piston 13 - Pin
3- Spool 7- Lever 1 11 - Spring 14 - Servo Piston
4- Pin 8- Hole

T3-1-6
 COMPONENTS OPERATION / Pump Device
Cross Section B-B

15 16 17 18 19 20 21 22 23
Pz

PG

24

T117-02-01-007C

15 - Piston 18 - Pin 21 - Outer Spring 23 - Piston

16 - Compensating Piston 19 - Hole 22 - Inner Spring 24 - Pin
17 - Lever 2 20 - Compensating Piston

T3-1-7
 COMPONENTS OPERATION / Pump Device
Cross Section (Regulator for Fan Motor Drive
Pump)
A
B

A B T183-03-01-102

Cross Section A-A

1 2 3 5 6 25 7 8 9 10 11

Pi

14 13 12

T146-03-01-008C

1- Inner Spring 6- Pin 10 - Pilot Piston 13 - Pin

2- Sleeve 7- Lever 1 11 - Spring 14 - Servo Piston
3- Spool 8- Hole 12 - Feedback Lever 25 - Pin
5- Pin 9- Pin

T3-1-8
 COMPONENTS OPERATION / Pump Device

Cross Section B-B

15 16 17 18 19 20 21 22

24

T146-03-01-005C

15- Piston 18- Pin 20- Compensating Piston 22- Inner Spring
16- Compensating Piston 19- Hole 21- Outer Spring 24- Pin
17- Lever 2

T3-1-9
 COMPONENTS OPERATION / Pump Device
Link Mechanism

Movement of pilot piston (10) is transmitted to lever 1 For this reason, when lever 1 (7) or lever 2 (17) ro-
(7) via pin (9). Lever 1 (7) rotates around pin (4), tates, pin (5) comes into contact with the hole edge on
which is fixed to the support plug. the lever, and is moved further. As a result, feedback
Movement of compensating rod (20) is transmitted to lever (12) rotates around pin (13) located on servo
lever 2 (17) via pin (24). Lever 2 (17) rotates around piston (14). On the other hand, when compensating
pin (18), which is fixed to the housing. rod (20) and pilot piston (10) are not moved, i.e. lev-
Pin (5) is threaded through a hole on feedback lever ers 1 and 2 do not move, and when servo piston (14)
(12), and the ends of pin (5) are inserted in a hole on is moved, feedback lever (12) rotates around pin (5),
levers 1(7) and 2 (17) respectively. (The hole is larger so that spool (3) moves.
than the pin (5) diameter.)

18 NOTE: To decrease swash angle

24 To increase swash angle
17
Housing 19

12

20
6
5

7
8
4
9

3 Support Plug

13

10

14
T117-02-01-009CCC

3- Spool 7- Lever 1 12- Feedback Lever 18- Pin

4- Pin 8- Hole 13- Pin 19- Hole
5- Pin 9- Pin 14- Servo Piston 20- Compensating Rod
6- Pin 10- Pilot Piston 17- Lever 2 24- Pin

T3-1-10
 COMPONENTS OPERATION / Pump Device
(Blank)

T3-1-11
 COMPONENTS OPERATION / Pump Device
Constant Torque Control

• Overload Preventing Operation

1. If pump delivery pressure P rises from P1 to P2, 7. As servo piston (14) moves, feedback lever (12)
compensating piston (16) moves compensating moves via pin (13). Since compensating rod (20)
rod (20) to the right until it balances with outer and lever 2 (17) do not move, feedback lever (12)
spring (21) and inner spring (22). rotates counterclockwise around pin (5), shifting
spool (3) to the left until the notches on spool (3)
2. Movement of compensating rod (20) is transmit- and sleeve (2) close completely. As these
ted to lever 2 (17) via pin (24), rotating lever 2 notches close, the pump pressure stops acting
(17) counterclockwise around pin (18). on the servo piston large chamber. Consequently,
the movement of servo piston (14) stops.
3. Since pin (5), which is connected to feedback
lever (12), is inserted into hole (19) on lever 2 8. With the above operation, the pump delivery flow
(17), feedback lever (12) rotates around pin (13) rate decreases from Q1 to Q2, relieving exces-
clockwise as lever 2 (17) rotates, moving spool sive load otherwise applied to the pump.
(3) to the right.

4. As spool (3) is moved, pump pressure P is routed

to the servo piston large chamber via spool (3).
Although pump pressure P is also routed to the
servo piston small chamber, servo piston (14) is
moved to the right due to the difference in pres- Q
sure receiving area between the servo piston (Flow Rate)
ends.
Q1

5. As servo piston (14) is moved to the right, the Q2

pump displacement angle decreases corre-
sponding to the distance that servo piston (14)
has moved, decreasing the pump delivery flow
rate.
P1 P2 P (Pump Delivery
6. As the pump pressure P acts on the compensat- Pressure)
ing piston (16), compensating rod (20) and lever
2 (17) do not move even if servo piston (14)
moves.

T3-1-12
 COMPONENTS OPERATION / Pump Device

1 2 16 3 17 18 5 19 20 21 22
Pz

PG

Large Chamber Small Chamber Pressure

(P1 → P2)

14 13 12 24

18
T117-02-01-010C
24
17
Housing 19

12
20

14

13

T117-02-01-009C
1- Spring 12- Feedback Lever 17- Lever 2 21- Outer Spring
2- Sleeve 13- Pin 18- Pin 22- Inner Spring
3- Spool 14- Servo Piston 19- Hole 24- Pin
5- Pin 16- Compensating Piston 20- Compensating Rod

T3-1-13
 COMPONENTS OPERATION / Pump Device
• Flow Rate Recovery Operation

1. If pump pressure P drops from P2 to P1, com- 6. As servo piston (14) is moved and because com-
pensating piston (16) (along with compensating pensating rod (20) and lever 2 (17) do not move,
rod (20)) is returned to the left until it balances feedback lever (12), which is connected to servo
against outer spring (21) and inner spring (22). piston (14) via pin (13), also rotates clockwise
around pin (5), moving spool (3) to the right until
2. Movement of compensating rod (20) is transmit- the notches on sleeve (2) are completely closed,
ted to lever 2 (17) via pin (24), rotating lever 2 thus closing the line from the servo piston large
(17) clockwise around pin (18) which is fixed to chamber to the hydraulic oil tank. As a result,
the housing. movement of servo piston (14) stops

3. Since pin (5), which is connected to feedback 7. With the above operation, the pump delivery flow
lever (12), is inserted into hole (19) on lever 2 rate increases from Q2 to Q1.
(17), feedback lever (12) rotates around pin (13)
counterclockwise as lever 2 (17) rotates, moving
spool (3) to the left
Q
4. Since pin (5), which is connected to feedback (Flow Rate)
lever (12), is inserted into hole (19) on lever 2 Q1
(17), feedback lever (12) rotates around pin (13)
Q2
counterclockwise as lever 2 (17) rotates, moving
spool (3) to the left

5. As servo piston (14) is moved to the left, the

pump displacement angle increases correspond-
ing to the distance that servo piston (14) has P1 P2 P (Pump Delivery
moved, increasing the pump delivery flow rate. Pressure)

T3-1-14
 COMPONENTS OPERATION / Pump Device

2 16 3 17 18 19 5 20 21 22 Pz

PG

Large Chamber Small Chamber Pressure

(P2 → P1)

14 13 12 24

Housing 18 T117-02-01-011C
24
17
19

20
12

14

13

T117-02-01-009C
2- Sleeve 13- Pin 18- Pin 21- Outer Spring
3- Spool 14- Servo Piston 19- Hole 22- Inner Spring
5- Pin 16- Compensating Piston 20- Compensating Rod 24- Pin
12- Feedback Lever 17- Lever 2

T3-1-15
 COMPONENTS OPERATION / Pump Device
Flow Rate Control

• Flow Rate Increasing Operation

1. On the main pump, flow rate control pressure Pi 6. As servo piton (14) is moved and because pilot
acts on pilot piston (10) by operating the control piston (10) and lever 1 (7) do not move, feedback
lever. On the oil cooler fan motor drive pump, lever (12), which is connected to servo piston
flow rate control pressure Pi from fan pump so- (14) via pin (13), rotates clockwise around pin (5),
lenoid valve SF acts on pilot piston (10). moving spool (3) to the right until the notches on
As pressure Pi increase, pilot piston (10) is sleeve (2) are completely closed, thus closing the
moved to the right until pilot piston (10) balances line from the servo piston large chamber to the
against spring (11). hydraulic oil tank. As a result, movement of servo
piston (14) stops.
2. As lever 1 (7) is connected to pilot piston (10) via
pin (9), movement of pilot piston (10) rotates 7. With the above operation, the pump delivery flow
lever 1 (7) counterclockwise around pin (4) which rate is increased in proportion to the increment of
is fixed to the support plug. pressure Pi.

3. Because pin (5) on feedback lever (12) is in- NOTE: Refer to the SYSTEM / Hydraulic System /
serted into hole (8) on lever 1 (7), feedback lever Pilot Circuit description.
(12) rotates counterclockwise around pin (13) as
lever 1 (7) rotates, moving spool (3) to the left. Q
(Flow Rate)
4. As spool (3) is moved, pressure oil in the servo
piston large chamber is routed to the hydraulic oil
tank via spool (3). Since pump pressure P is
routed to the servo piston small chamber all the
time, servo piston (14) is moved to the left.

5. As servo piston (14) is moved to the left, the

pump displacement angle increases correspond-
ing to the distance that servo piston (14) has Pi (Flow Rate Control
Pressure)
moved, increasing the pump delivery flow rate.

T3-1-16
 COMPONENTS OPERATION / Pump Device

2 3 4 7 8 5 10 11

Pi

14 13 12 9

Housing T117-02-01-012C

12

7
4

Support Plug

14

13

10

T117-02-01-009C

2- Sleeve 5- Pin 9- Pin 12- Feedback Lever

3- Spool 7- Lever 1 10- Pilot Piston 13- Pin
4- Pin 8- Hole 11- Spring 14- Servo Piston

T3-1-17
 COMPONENTS OPERATION / Pump Device
• Flow Rate Decreasing Operation

1. On the main pump, the pressure Pi decreases by 6. As servo piston (14) moves, feedback lever (12)
returning the control lever, so that pilot piston moves via pin (13). Since pilot piston (10) and
(10) is returned to the left until it, or pressure Pi in lever 1 (7) do not move, feedback lever (12) ro-
other words, balances against spring (11). tates counterclockwise around pin (5), shifting
On the oil cooler fan motor drive pump, the spool (3) to the left until the notches on spool (3)
pressure Pi from fan pump solenoid valve SF de- and sleeve (2) closes completely. As these
creases, so that pilot piston (10) is returned to notches close, the pump pressure stops acting
the left until it, or pressure Pi in other words, bal- on the servo piston large chamber. Consequently,
ances against spring (11). the movement of servo piston (14) stops.

2. As lever 1 (7) is connected to pilot piston (10) via 7. With the above operation, the pump delivery flow
pin (9), movement of pilot piston (10) rotates rate is decreased in proportion to the degree of
lever 1 (7) clockwise around pin (4) which is fixed the decrement of pressure Pi.
to the support plug.
NOTE: Refer to the SYSTEM / Hydraulic System /
3. Because pin (5) on feedback lever (12) is in- Pilot Circuit description.
serted into hole (8) on lever 1 (7), feedback lever
(12) rotates clockwise around pin (13) as lever 1
Q
(7) rotates, moving spool (3) to the right.
(Flow Rate)
4. As spool (3) is moved, pump pressure P is routed
to the servo piston large chamber via spool (3).
Although pump pressure P is also routed to the
servo piston small chamber, servo piston (14) is
moved to the right due to the difference in pres-
sure receiving area between the servo piston
ends.
Pi (Flow Rate Control
5. As servo piston (14) is moved to the right, the Pressure)
pump displacement angle decreases corre-
sponding to the distance that servo piston (14)
has moved, decreasing the pump delivery flow
rate.

T3-1-18
 COMPONENTS OPERATION / Pump Device

2 3 4 7 5 8 10 11

Pi

14 13 12 9

T117-02-01-013C

12

7
4

Support Plug

14

13

10

T117-02-01-009C

2- Sleeve 5- Pin 9- Pin 12- Feedback Lever

3- Spool 7- Lever 1 10- Pilot Piston 13- Pin
4- Pin 8- Hole 11- Spring 14- Servo Piston

T3-1-19
 COMPONENTS OPERATION / Pump Device
Horsepower Reducing Control (only for Main
Pump)

1. Horsepower reducing control pressure PG acts 6. As servo piston (14) moves, feedback lever (12)
on piston (15). When pressure PG acts on piston moves via pin (13). Since compensating rod (20)
(15), compensating piston (16) and compensat- and lever 2 (17) do not move, feedback lever (12)
ing rod (20) move until they balance against rotates counterclockwise around pin (5), shifting
outer spring (21) and inner spring (22). spool (3) to the left until the notches on spool (3)
and sleeve (2) close completely. As these
2. Movement of compensating rod (20) is transmit- notches close, the pump pressure stops acting
ted to lever 2 (17) via pin (24), rotating lever 2 on the servo piston large chamber. Consequently,
(17) counterclockwise around pin (18). the movement of servo piston (14) stops.

3. Since pin (5), which is connected to feedback 7. With the above operation, the P-Q curve is reset
lever (12), is inserted into hole (19) on lever 2 as illustrated (when horsepower reducing control
(17), feedback lever (12) rotates around pin (13) pressure PG acts on piston (15)). Consequently,
clockwise as lever 2 (17) rotates, moving spool the torque constant control (overall preventing
(3) to the right. operation and delivery flow rate decreasing op-
eration) is performed on this reset P-Q curve.
4. As spool (3) is moved, pump pressure P is routed
to the servo piston large chamber via spool (3). NOTE: Refer to the SYSTEM / Hydraulic System /
Although pump pressure P is also routed to the Pilot Circuit description.
servo piston small chamber, servo piston (14) is
moved to the right due to the difference in pres-
sure receiving area between the servo piston Q
ends. (Flow Rate)

5. As servo piston (14) is moved to the right, the

pump displacement angle decreases corre-
sponding to the distance that servo piton (14) has
moved, decreasing the pump delivery flow rate.

P(Pressure)

T3-1-20
 COMPONENTS OPERATION / Pump Device

15 2 16 3 17 18 5 19 20 21 22 Pz

PG

14 13 12 24

Housing 18 T117-02-01-014C
24
17
19

20
12

14

13

T117-02-01-014
2- Sleeve 13- Pin 17- Lever 2 21- Outer Spring
3- Spool 14- Servo Piston 18- Pin 22- Inner Spring
5- Pin 15- Piston 19- Hole 24- Pin
12- Feedback Lever 16- Compensating Piston 20- Compensating Rod

T3-1-21
 COMPONENTS OPERATION / Pump Device
Horsepower Increasing Control (only for Main
Pump)

1. When horsepower increasing control pressure Pz 6. As servo piston (14) is moved and because com-
rises, piston (23) moves compensating rod (20) pensating rod (20) and lever 2 (17) do not move,
to the left until it balances against pump pressure feedback lever (12), which is connected to servo
P which is acting on compensating piston (16). piston (14) via pin (13), rotates clockwise around
pin (5), moving spool (3) to the right until the
2. Movement of compensating rod (20) is transmit- notches on sleeve (2) are completely closed,
ted to lever 2 (17) via pin (24), rotating lever 2 thus closing the line from the servo piston large
(17) clockwise around pin (18) which is fixed to chamber to the hydraulic oil tank. As a result,
the housing. movement of servo piston (14) stops.

3. Since pin (5), which is connected to feedback 7. With the above operation, the P-Q curve is reset
lever (12), is inserted into hole (19) on lever 2 as illustrated (when horsepower increasing con-
(17), feedback lever (12) rotates around pin (13) trol pressure Pz rises). Consequently, the con-
counterclockwise as lever 2 (17) rotates, moving stant torque control (overload preventing opera-
spool (3) to the left. tion and delivery flow rate increasing operation)
is performed on this reset P-Q curve.
4. As spool (3) is moved, pressure oil in the servo
piston large chamber is routed to the hydraulic oil NOTE: Refer to the SYSTEM / Hydraulic System /
tank via spool (3). Since pump pressure P is Pilot Circuit description.
routed to the servo piston small chamber all the
time, servo piston (14) is moved to the left. Q
(Flow Rate)
5. As servo piston (14) is moved to the left, the
pump displacement angle increases correspond-
ing to the distance that servo piston (14) has
moved, increasing the pump delivery flow rate.

P(Pressure)

T3-1-22
 COMPONENTS OPERATION / Pump Device

2 16 3 17 18 19 5 20 21 22 23 Pz

PG

14 13 12 24

Housing 18 T117-02-01-015C
24
17
19

20
12

14

13

T117-02-01-014
2- Sleeve 13- Pin 18- Pin 22- Inner Spring
3- Spool 14- Servo Piston 19- Hole 23- Piston
5- Pin 16- Compensating Piston 20- Compensating Rod 24- Pin
12- Feedback Lever 17- Lever 2 21- Outer Spring

T3-1-23
 COMPONENTS OPERATION / Pump Device
Smaller Swash Angle (Less Flow Rate) Priority
Control

The swash plate angle control by flow rate control or

increasing/reducing horsepower control is transmit-
ted to feedback lever (12) and spool (3) through hole
(8) on lever 1 (7) and hole (19) on lever 2 (17) via pin
(5). (Refer to Flow Rate Control, Horsepower In-
creasing Control and Horsepower Reducing Con-
trol).
Pin (5) comes into contact against the sides which
decreases swash plate angle, placed in holes (8)
and (19) on lever 1 (7) and lever 2 (17). Therefore,
the flow rate reducing and horsepower reducing
controls are selected with preferentially.

T3-1-24
 COMPONENTS OPERATION / Pump Device
Cross Section
3 7 5 8

Pi

12

T117-02-01-013C

3 17 5 19 Pz

PG

T117-02-01-014C

3- Spool 7- Lever 1 12- Feedback Lever 19- Hole

5- Pin 8- Hole 17- Lever 2

T3-1-25
 COMPONENTS OPERATION / Pump Device
3-UNIT PUMP
The engine power is transmitted through the pump
transmission to the shaft. As the shaft turns, the three
pumps are operated simultaneously.
The oil cooler fan motor drive pump (A) is a variable
displacement swash plate plunger type pump. It has
the cylinder block splined to the shaft. As the shaft
and cylinder block rotate, the plungers move in and
out of their bores, drawing and pushing hydraulic oil.
Pilot pump (B) and transmission oil circulation pump
(C) are gear type pumps. The shaft drives the drive
gear, and the driven gear are driven by the drive gear.
Hydraulic oil drawn into the pump housings are deliv-
ered to the outlets along the housing inner surfaces.

C B A

T183-03-01-003

A- Oil Cooler Fan Motor Drive Pump C- Transmission Oil Circulation Pump
(Variable Displacement Swash Plate Plunger Type Pump) (Tandem Gear Pump)
B- Pilot Pump (Tandem Gear Pump)

Suction Side

Driven Gear Drive Gear

Housing
Delivery Side
(Outlet)

T137-02-03-005C

T3-1-26
 COMPONENT OPERATION / Swing Device
OUTLINE
The swing device consists of the valve unit, motor , The reduction gear functions to reduce the rotation
and reduction gear. speed of swing motor and to increase its torque
The motor is driven by pressure oil from the pump and before transmitting the rotational force from swing
transmits rotational force to the reduction gear. moter to the pinion shaft.
The valve unit functions to protect the swing circuit.

Motor Valve Unit

Reduction Gear

T142-02-02-001

T3-2-1
 COMPONENT OPERATION / Swing Device
SWING MOTOR
The swing motor is a swash-plate-type axial plunger The spherical end of plunger (5) is installed in shoe
motor. (2) by a ball-and-socket joint. The shaft part of plunger
The swing motor consists of shaft (4), swash plate (3), (5) is inserted into rotor (6). Rotor (6) is installed onto
shoes (2), plungers (5), rotor (6), valve plate (9), shaft (4) with a spline coupling.
housing (1), and parking brake. The parking brake is a wet-type multiple disc brake,
consisting of friction plates (7) and plates (8).

7 1
6
2

5
3

T142-02-02-002

1 - Housing 4 - Shaft 6 - Rotor 8 - Plate

2 - Shoe 5 - Plunger 7 - Friction Plate 9 - Valve Plate
3 - Swash Plate

T3-2-2
 COMPONENT OPERATION / Swing Device
Operational Principle
Swing speed varies depending on the amount of oil The rotational force is then transmitted to the swing
delivered from the pump. reduction gear via the shaft. As the rotor is rotated,
When pressure oil is fed into the rotor bores via port the plungers are moved to port (B) side one by one,
(A), the plungers are pushed from the top dead returning oil to the hydraulic oil tank. When pressure
center to the bottom dead center causing the shoes oil is fed via port (B), the motor rotates in the
to slide along the swash plate, developing rotational opposite direction
force.

Plunger

Shoe

Shaft

T142-02-02-004

T3-2-3
 COMPONENT OPERATION / Swing Device
VALVE UNIT
The valve unit consists of the make-up valve and the
relief valve.
Drain Port
Make-Up Valve
When swing is stopped, the upperstructure tends to Make-Up Valve
keep rotating due to swing inertia force, causing the
Port M
swing motor to continue rotating further, and to begin Make-Up Port
drawing oil from the pump, developing cavitation the
motor.
The make-up valve draws hydraulic oil through the Relief Valve
Port M (Return Circuit) to compensate for the lack of
oil, and prevent cavitation.
Control Valve

T142-02-02-005

Relief Valve

Make-Up Valve

Control Valve

T140-02-04-002

T3-2-4
 COMPONENT OPERATION / Swing Device
Relief Valve
When starting or stopping swing operation, oil
pressure in the swing circuit becomes high. The
relief valve prevents the circuit pressure from rising
higher than the specified pressure. Plunger is
pushed to the left by pressure Pp at port (P) and
pressure-receiving area A2.
However, plunger is also pushed back to the right by
spring force and pressure Pg at chamber (g) and
pressure-receiving area A1.
Chamber (g) is connected to port (P) through orifice
(m). When force acting on the right is higher than Relief Valve
that on the left, the relief valve operates.

Control Valve

T142-02-02-005

Spring A1 Plunger A2

Port P

Chamber (g) m
T142-02-02-006

T3-2-5
 COMPONENT OPERATION / Swing Device
SWING PARKING BRAKE
When the brake is released (OFF): Pressure Oil
The swing parking brake is a wet-type multiple disc from Pilot
brake. Swing Parking Signal Circuit
1 Brake Release via Shuttle
Also, the swing parking brake is a negative type, i.e. Valve Valve
the brake is released when brake release pressure is
routed into brake-piston chamber (b).
The brake release pressure is supplied from the pilot
pump when a control lever is operated.
When the control levers are in neutral (or while the
engine is stopped), the brake release pressure is
returned to the hydraulic oil tank and the swing
parking brake is automatically applied by spring (1).
(Refer to the pilot circuit diagram in the Hydraulic
Brake Release
System Group of the System Section.)
Chamber (b) Pressure from
Pilot Pump
• When Parking Brake is Released (OFF) (When 2
Control Lever is Operated) 6 3 4 5
When a control lever is operated, the pressure in T142-02-02-007

the pilot signal circuit rises because the

corresponding control valve spool is shifted. The
pressure in the pilot signal circuit acts on the
switch valve of the parking brake release valve,
When the brake is applied (ON):
shifting it. As the switch valve is shifted, the brake
release pressure from the pilot pump is routed
into chamber (b) via the swing parking release Drain Port
valve, acting on and pushing brake piston (2). As
a result, plates (3) and friction plates (4) become
contact free with each other, thus releasing the
parking brake.

• When Parking Brake is Applied (ON) (When

Control Levers are in Neutral.)
When the control levers are in neutral, the
pressure in the pilot signal circuit does not rise.
For this reason, the switch valve is not shifted 7
5 Chamber (b)
and the parking brake release pressure is not 4
routed to chamber (b). The pressure oil in 3
6 T142-02-02-007

chamber (b) is released to the motor drain port.

Thus, plates (3), which are secured to the outer
circumference of rotor (6), and friction plates (4),
which are secured to the inner wall of motor
housing (5), are pushed by spring (1) via brake
piston (2), coming into tight contact with each
other. As a result, rotor (6) is secured immovable,
thus applying the swing parking brake.

1- Spring 5 - Motor Housing

2- Brake Piston 6 - Rotor
3- Plate 7 - Orifice
4- Friction Plate

T3-2-6
 COMPONENT OPERATION / Swing Device
SWING REDUCTION GEAR
The swing reduction gear is a planetary-gear-type two The motor shaft rotates first stage sun gear (9). As the
stage reduction gear. first stage reduction takes place between first stage
Both first and second stage ring gears are immovable planetary gears (1) and first stage carrier (7), second
because they are fixed to the housing. stage sun gear (5) is rotated. Then, the second stage
reduction takes place between second stage
planetary gears (2) and second stage carrier (4)
before the rotational force is transmitted to shaft (3).

9
1

7 2

4
3

W142-02-06-003

1 - First Stage Planetary Gear 4 - Second Stage Carrier 6 - Second Stage Ring Gear 8 - First Stage Ring Gear
2 - Second Stage Planetary 5 - Second Stage Sun Gear 7 - First Stage Carrier 9 - First Stage Sun Gear
Gear
3 - Shaft

T3-2-7
 COMPONENT OPERATION / Swing Device
(Blank)

T3-2-8
 COMPONENT OPERATION / Control Valve
OUTLINE
Two kinds of control valves, main control valve and 4-Spool Section: Right travel, Bucket 1, Boom 1, and
swing control valve, are used on this machine. The arm 2 in that order viewed from the front side. 5-Spool
control valve regulates oil pressure, flow rate and flow Section: Left Travel, Bucket 2, Boom 2, Arm 1, and
direction in the hydraulic circuit. The main control Auxiliary in that order viewed from the front side.
valve consists of two blocks, the 5-spool and 4-spool Swing Control Valve: Boom 3, Swing, Bucket 3, and
blocks. The swing control valve is a one block arm 3 in that order viewed from the front side. Pres-
(4-spool) type. Major components of the control valve sure oil from the pilot pump is routed to the signal pilot
are a main relief valve, oil flow combiner valve, and pressure circuit to control each operation.
spools. Both the main and swing control valves are NOTE: BH: Backhoe
pilot-pressure operated type. The spool arrangements LD: Loading Shovel
in the control valve are as follows:

Left Travel
Bucket 2
Main Control Valve Front Side Right Travel
Arm Regenerative Valve Bucket 1
Boom 1
Make-Up Valve
(Arm 2) Boom 2 Arm 2
Overload Relief
Slow Valve (Boom
Return Mode Selection)
Valve
Overload Re-
lief Valve
(Bucket 2) 4-Spool
Block
Arm 1

Boom Overload Overload

Relief Pressure Relief Valve
Overload Re- 5-Spool Switch Valve (Aux.:BH,
lief Valve Block Bucket
Auxiliary (Backhoe) Open/Close:
(Boom)
Bucket Open/Close LD)
Overload Re- (Loading Shovel)
lief Valve 4-Spool
Holding Valve Overload Re-
(Bucket) Block Front Side
Switch Valve lief Valve
Main Relief 5-Spool
(Boom) Holding Valve (Arm)
Valve T183-03-03-029 Block
Switch Valve
Shuttle Valve (Arm) T183-03-03-028

Swing Control Valve

Holding Valve Switch
Valve
Front Side
(Boom) Mack-Up Valve
Main Relief (Arm 3)
Valve

Overload
Relief Valve
(Swing)
Boom 3
Swing
Bucket 3

Arm 3
T183-03-03-031
T183-03-03-030
Front Side

T3-3-1
 COMPONENT OPERATION / Control Valve
Main Control Valve Auxiliary: BH
2 3 4 5 6 7 8 9 Bucket
Open/Close: LD

10

34
Arm 1
Arm 2
11

33 Boom 2

Boom 1
12
32
13

31 14
Bucket 2
15
Bucket 1
16
30
17

Left Travel 18
29

28
Right Travel
19

27

26 25 24 23 22 21 20 T18E-03-03-001

NOTE: BH: Backhoe

LD: Loading Shovel
1 - Holding Valve Switch 10 - Overload Relief Valve 19 - Load Check Valve (Left 27 - Main Relief Valve
Valve (Boom) (Aux.: BH, Travel Tandem Circuit)
Bucket Open/Close: LD)
2 - Load Check Valve 11 - Overload Relief Valve 20 - Load Check Valve (Left 28 - Load Check Valve
(Arm 2 Tandem Circuit) (Arm) Travel Parallel Circuit) (Bucket 1 Tandem Circuit)
3 - Load Check Valve 12 - Holding Valve Check 21 - Load Check Valve 29 - Overload Relief Valve
(Arm 2 Parallel Circuit) Valve (Arm) (Bucket 2 Parallel Circuit) (Bucket 1)
4 - Arm Regenerative Valve 13 - Load Check Valve 22 - Check Valve (Main Relief 30 - Load Check Valve
(Boom 2 Tandem Circuit) Pressure Combining Circuit) (Boom1 Parallel Circuit)
5 - Load Check Valve 14 - Load Check Valve 23 - Flow Combiner Valve 31 - Overload Relief Valve
(Arm 1 Parallel Circuit1) (Boom 2 Parallel Circuit) (Boom)
6 - Load Check Valve 15 - Overload Relief Valve 24 - Check Valve (Travel Flow 32 - Holding Valve Check Valve
(Arm 1 Parallel Circuit2) (Boom Mode Selection) Combine Circuit) (Boom)
7 - Load Check Valve 16 - Boom Overload Relief 25 - Check Valve (Main Relief 33 - Slow Return Valve
(Auxiliary Tandem Circuit) Pressure Switch Valve Pressure Combining Circuit)
8 - Load Check Valve 17 - Load Check Valve 26 - Shuttle Valve 34 - Make-Up Valve (Arm 2)
(Arm 1 Tandem Circuit) (Bucket 2 Tandem Circuit)
9 - Holding Valve Switch 18 - Overload Relief Valve
Valve (Arm) (Bucket 2)

T3-3-2
 COMPONENT OPERATION / Control Valve

11 9 15, 16 18 Section A
G F E D C B A 26 27

25
10
Front

27
4
26

31 29
T183-03-03-003
24 23
T183-03-03-002
33 1
Section C 39 40
Section B 35 36

Right Travel Left Travel Bucket 1 Bucket 2

18
29

17

19 28

21

20
18

29
T183-03-03-004 T183-03-03-005

37 38 41 42

NOTE: BH: Backhoe

LD: Loading Shovel
35 - Right Travel (Forward) Port 37 - Left Travel (Reverse) Port 39 - Bucket 1 (Roll-Out : BH, 41 - Bucket 1 (Roll-In : BH,
Tilt-Out : LD) Port Tilt-In : LD) Port
36 - Left Travel (Forward) Port 38 - Right Travel (Reverse) Port 40 - Bucket 2 (Roll-Out : BH, 42 - Bucket 2 (Roll-In : BH,
Tilt-Out : LD) Port Tilt-In : LD) Port

T3-3-3
 COMPONENT OPERATION / Control Valve
Auxiliary: BH
2 3 4 5 6 7 8 9 Bucket
Open/Close: LD

10

34
Arm 1
Arm 2
11

33 Boom 2

Boom 1
12
32
13

31 14
Bucket 2
15
Bucket 1
16
30
17

Left Travel 18
29

28
Right Travel
19

27

26 25 24 23 22 21 20 T18E-03-03-001

NOTE: BH: Backhoe

LD: Loading Shovel
1 - Holding Valve Switch 10 - Overload Relief Valve 19 - Load Check Valve (Left 27 - Main Relief Valve
Valve (Boom) (Aux.: BH, Travel Tandem Circuit)
Bucket Open/Close: LD)
2 - Load Check Valve 11 - Overload Relief Valve 20 - Load Check Valve 28 - Load Check Valve
(Arm 2 Tandem Circuit) (Arm) (Left Travel Parallel Circuit) (Bucket 1 Tandem Circuit)
3 - Load Check Valve 12 - Holding Valve Check 21 - Load Check Valve 29 - Overload Relief Valve
(Arm 2 Parallel Circuit) Valve (Arm) (Bucket 2 Parallel Circuit) (Bucket 1)
4 - Arm Regenerative Valve 13 - Load Check Valve 22 - Check Valve (Main Relief 30 - Load Check Valve
(Boom 2 Tandem Circuit) Pressure Combining Circuit) (Boom1 Parallel Circuit)
5 - Load Check Valve 14 - Load Check Valve 23 - Flow Combiner Valve 31 - Overload Relief Valve
(Arm 1 Parallel Circuit1) (Boom 2 Parallel Circuit) (Boom)
6 - Load Check Valve 15 - Overload Relief Valve 24 - Check Valve (Travel Flow 32 - Holding Valve Check Valve
(Arm 1 Parallel Circuit2) (Boom Mode Selection) Combine Circuit) (Boom)
7 - Load Check Valve 16 - Boom Overload Relief 25 - Check Valve (Main Relief 33 - Slow Return Valve
(Auxiliary Tandem Circuit) Pressure Switch Valve Pressure Combining Circuit)
8 - Load Check Valve 17 - Load Check Valve 26 - Shuttle Valve 34 - Make-Up Valve (Arm 2)
(Arm 1 Tandem Circuit) (Bucket 2 Tandem Circuit)
9 - Holding Valve Switch 18 - Overload Relief Valve
Valve (Arm) (Bucket 2)

T3-3-4
 COMPONENT OPERATION / Control Valve

43 44
Section D Section E 47 4 48

Boom 1 Boom 2

Arm 2 Arm 1
16 12
33 34
31 9
15

13
30

3 8
14
2
11
31
T183-03-03-007

49 50
1 32 46
T183-03-03-006

45 51
10
Auxiliary (BH) Section G
Section F Bucket Open/Close (LD)

11

T183-03-03-009
9
34 52
T183-03-03-008

43 - Boom 1 (Lower) Port 46 - Boom 2 (Raise) Port 49 - BH: Arm 2 (Roll-In) Port 51 - BH: Auxiliary Port
LD: Arm 2 (Extend) Port LD: Bucket (Open) Port
44 - Boom 2 (Lower) Port 47 - BH: Arm 2 (Roll-Out) Port 50 - BH: Arm 1 (Retract) Port 52 - BH: Auxiliary Port
LD: Arm 2 (Retract) Port LD: Arm 1 (Extend) Port LD: Bucket (Open) Port
45 - Boom 1 (Raise) Port 48 - BH: Arm 1 (Roll-Out) Port
LD: Arm 1 (Roll-In) Port

T3-3-5
 COMPONENT OPERATION / Control Valve
Swing Control Valve

1 2

11
Boom 3

10 3

Swing
4

Bucket 3

5
9

Arm 3
6

8 7 T18E-03-03-002

1 - Main Relief Valve 4 - Load Check Valve 7 - Check Valve (Arm 3) 10 - Holding Valve Switch Valve
(Bucket 3)
2 - Load Check Valve (Boom 5 - Load Check Valve (Arm 3) 8 - Make-Up Valve (Arm 3) 11 - Holding Valve Check Valve
3) (Boom 3)
3 - Load Check Valve (Swing) 6 - Load Check Valve 9 - Overload Relief Valve
(Arm 3 Parallel Circuit) (Swing)

T3-3-6
 COMPONENT OPERATION / Control Valve

12 14 16 18
Section A

1
B C D E F

1 10 9 T183-03-03-011

T183-03-03-012
13 15 17 19

Section C 14
Section B 11

Swing
Boom 3
9

10

9
T183-03-03-014
11
T183-03-03-013 15
13

12 - Boom 3 (Lower) Port 13 - Boom 3 (Raise) Port 14 - Swing (Left) Port 15 - Swing (Right) Port

T3-3-7
 COMPONENT OPERATION / Control Valve

1 2

11
Boom 3

10 3

Swing
4

Bucket 3

5
9

Arm 3
6

8 7 T18E-03-03-002

4 - Main Relief Valve 7 - Load Check Valve 10 - Check Valve (Arm 3) 12 - Holding Valve Switch Valve
(Bucket 3)
5 - Load Check Valve (Boom 8 - Load Check Valve (Arm 3) 11 - Make-Up Valve (Arm 3) 13 - Holding Valve Check Valve
3) (Boom 3)
6 - Load Check Valve (Swing) 9 - Load Check Valve 12 - Overload Relief Valve
(Arm 3 Parallel Circuit) (Swing)

T3-3-8
 COMPONENT OPERATION / Control Valve
16 18
Section D Section E

Bucket 3 Arm 3

4
6

T183-03-03-015
T183-03-03-016
17 19 7
Section F

T183-03-03-017
7
NOTE: BH: Backhoe
LD: Loading Shovel
16 - Bucket 3 (Roll-Out) Port 17 - Bucket 3 (Roll-In) Port 18 - BH: Arm 3 (Roll-Out) Port 19 - BH: Arm 3 (Roll-In) Port
LD: Arm 3 (Retract) Port LD: Arm 3 (Extend) Port

T3-3-9
 COMPONENT OPERATION / Control Valve
HYDRAULIC CIRCUIT
Main Circuit
Pressure oil from main pump 1, main pump 2, and
main pump 3 are routed to the 5-spool section of the
main control valve, the 4-spool section of the main
control valve, and the swing control valve respec-
tively. Each main circuit is provided with a parallel
circuit, making combined operations possible. The
main relief valve regulates the maximum oil pressure
in the main circuit. Overload relief valves are pro-
vided in the boom, arm, bucket, swing, and auxiliary
circuits.

Pilot Control Circuit

Pressure oil (indicated by figure No.) from the pilot
valve acts on the spool ends in the control valve to
operate the spools.

External Pilot Pressure Circuit

• Pilot Pressure from boom mode selection solenoid
valve (SC) shifts the boom overload relief pressure
switch valve.
(Refer to the SYSTEM / Control System group.)
• Pilot pressure from the flow combiner valve control
spool in the signal control valve shifts the flow
combiner valve.
(Refer to the SYSTEM / Hydraulic System group.)

T3-3-10
 COMPONENT OPERATION / Control Valve

From Flow Combiner

Valve Control Spool in Main Relief
Signal Control Valve Valve

Main Relief Overload

Valve Relief Valve

Flow Combiner Valve

1 2
9 10
12 11

7 8
6 7 8 7

8 1 1 2
Boom Over- 2 1
load Relief
Pressure
Switch Valve
3 4 4 3
3 4

14 13 Overload
Relief Valve
Overload
Relief Valve
Overload
Relief Valve
Main Pump 1
From Boom
Mode Selection Main Pump 2
Solenoid Valve
Main Pump 3

T18E-03-03-003

1 - Boom Raise 5 - Left Swing 9 - Left Travel Forward 12 - Right Travel Reverse
2 - Boom Lower 6 - Right Swing 10 - Left Travel Reverse 13 - Bucket Close
(Loading Shovel)
3 - Arm Roll-Out (Backhoe) 7 - Bucket Roll-In (Backhoe) 11 - Right Travel Forward 14 - Bucket Open
Arm Retract (Loading Bucket Tilt-In (Loading Shovel) (Loading Shovel)
Shovel)
4 - Arm Roll-In (Backhoe) 8 - Bucket Roll-Out (Backhoe)
Arm Roll-Out (Load- Bucket Tilt-Out (Loading Shovel)
ing Shovel)

T3-3-11
 COMPONENT OPERATION / Control Valve
FLOW COMBINER VALVE
1. Normally, the spring pushes the spool, blocking
the valve ports.
2. When the front attachment and travel control lev-
ers are operated at the same time, the right travel
pilot oil pressure shifts the flow combiner valve
control spool in the signal control valve so that
the pilot pressure shifts the flow combiner valve
spool.
3. When the flow combiner valve spool is shifted,
pressure oil from main pump 2 is routed to the
left travel spool.
4. Therefore, pressure oil from main pump 2 is
routed to the left travel spool in parallel with the
right travel spool and pressure oil from main
pump 1 is routed to the front attachment. Con-
sequently, the machine can travel straight when a
combine operation of travel and front attachment
is performed.

Travel Motor Travel Motor (Right)

Flow Combiner Valve Pilot Pressure from Flow Combiner Valve

Control Spool in Signal Pilot Pressure Control
Valve

Spring

Main Pump 2 T183-03-03-022

T3-3-12
 COMPONENT OPERATION / Control Valve
In Neutral: In Operation:
Spring Spring

Spool Spool

To Left Travel To Left Travel

Spool Spool

Pressure Oil from Pressure Oil from

Main Pump 2 Main Pump 2

Pilot Pressure
from Flow Com-
biner Valve Con-
trol Spool
T183-03-03-023 T183-03-03-024

T3-3-13
 COMPONENT OPERATION / Control Valve
MAIN RELIEF VALVE
Main relief valve set pressure is shifted in two stages High Relief Pressure Setting
by the pilot pressure from the heavy lift solenoid valve. When the heavy lift switch is turned ON, the heavy
When the heavy lift system is activated, the main relief lift solenoid valve is magnetized by main controller A
pressure is set in the high stage. When the heavy lift so that the pilot pressure is routed to shuttle valve
system is deactivated, the main relief pressure is set PF1.
in the low stage. Then, the pilot pressure pushes the piston to the left,
compressing the spring. Then, the pilot poppet is
Low Relief Pressure Setting pushed by increased force, increasing the main relief
When the heavy lift switch is turned OFF, the heavy valve set-pressure. The relief valve operation is the
lift solenoid valve is demagnetized so that the signal same as that in the low relief set-pressure.
pilot pressure is not routed to shuttle valve PF1.
Since shuttle valve PF2 is connected to the hydraulic
oil tank, the piston doesn’t move to the left, reducing
pilot poppet pushing force. When pressure at port
HP increases over the spring set-force, the pilot
poppet is unseated, allowing pressure oil to flow to
port LP through passage A. When the pilot poppet is
unseated, pressure in the spring chamber A is re-
duced so that the main poppet is unseated, allowing
pressure oil to flow from port HP to port LP.

Main Poppet Pilot Poppet Spring Piston

LP

HP

LP

PF2 PF1 Shuttle Valve

Spring Chamber A Passage A Heavy Lift Solenoid Valve

T111-02-05-014

T3-3-14
 COMPONENT OPERATION / Control Valve
OVERLOAD RELIEF VALVE
(With Make-Up Function)
1 2 a 3 4
Overload relief valves are provided at the output ports
to the swing motors, and the boom, arm, and bucket HP
cylinders. The overload relief valve prevent the ac-
tuator circuit pressure from increasing excessively
when the actuator(s) is (are) moved by external loads.
When pressure in port HP increases up to set-force of
spring (4), pilot poppet (3) is unseated, allowing
pressure oil to flow to port LP from chamber (a) via LP
the clearance around main poppet (2). Then, pressure
difference arises between port HP and chamber (a)
T111-02-05-019C
due to the orifice located between them. When this 5 Orifice
pressure difference increases over set-force of spring
(5), piston (1) and main poppet (2) are unseated so a
1 2
that pressure oil flows directly to port LP from port HP.
In addition, this relief valve draws oil from the hydrau-
lic oil tank if pressure in the actuator becomes nega- HP
tive to prevent cavitation in the circuit (make-up func-
tion).

1 - Piston 4 - Spring
2 - Main Poppet 5 - Spring
3 - Pilot Poppet LP

T111-02-05-021C

MAKE-UP VALVE
7 6
Make-up valves are provided at the output ports of the d1
arm 2 and 3 spool sections, assisting the makeup d2
HP
function of the overload relief valve. When pressure in
port HP is higher than port LP, poppet (7) is kept
seated due to difference (d1-d2) in pressure receiving
areas on poppet (7). Therefore, when pressure in port
HP is reduced lower than port LP, poppet (7) is
pushed to the right to unseat due to difference (d1-d2)
LP
in pressure receiving areas on poppet (7).

6 - Spring 7 - Poppet b T111-02-05-023C

HP

LP

T111-02-05-024C

T3-3-15
 COMPONENT OPERATION / Control Valve
HOLDING VALVE
The holding valves are provided at the output ports of • In Neutral
the main control valve to the boom raise and the arm The cylinder holding pressure at cylinder port C is
roll-out circuit and at the output port of the swing con- routed to camber (a) through orifice (b) in check
trol valve to the boom raise circuit, preventing cylinder valve (2). Then, Check valve (2) is kept seated due
drift. to difference (d1-d2) in pressure receiving areas,
completely blocking cylinder port (c).

External Force
1

g
a
a
d1 2
Holding
b Pressure
g
c
b
d2 3
d c
3

Pi
f

T111-02-05-025C
f d e

• When lowering the boom or rolling the arm in: At the same time, spool (3) is shifted, pressure oil
Pilot pressure Pi is routed to switch valve (1), causing from (c) to (f) via (d) to allow the cylinder to move.
chamber (a) to connect to the hydraulic oil tank.
Then, pressure in chamber (a) is reduced so that
check valve (2) is unseated.

a
a

3
3
d c

Pi
f

T111-02-05-026C

1 - Switch Valve 2 - Check Valve 3 - Spool

T3-3-16
 COMPONENT OPERATION / Control Valve
(Blank)

T3-3-17
 COMPONENT OPERATION / Control Valve
ARM REGENERATIVE VALVE
1
The arm regenerative valve is provided to prevent arm PB
cylinder hesitation while rolling in the arm so that arm PR
controllability is greatly improved. i

8
The return oil flow from the cylinder rod side is re- 3
stricted in two stages at orifice (A) in spool (2) and ori- 2
fice (B) in arm regenerative valve so that pressure PR h
at the cylinder rod side increases. When pressure PR A
at the cylinder rod side increases more than pressure
PB at the cylinder bottom side, check valve (3) is
opened. Then, the return oil from the cylinder rod side e C
is combined with pressure oil from the pump and sup-
7
plied again to the cylinder bottom side.
b 6
9
d B
a

1
T111-02-05-035

PR PB
8 9

A
h

f e a i d
e
7 B
d
c

T111-02-05-028
6 5 4

1 - Arm Cylinder 4 - Piston 6 - Spring 8 - Holding Valve

2 - Spool 5 - Spool 7 - Arm Regenerative Valve 9 - Load Check Valve
3 - Check Valve

T3-3-18
 COMPONENT OPERATION / Control Valve
When pressure PB at the bottom side is higher than
the rod side, check valve (3) is closed, blocking the 1
return oil circuit. In addition, oil pressure from the PB
pump is routed to piston (4) end in arm regenerative PR
flow control valve (7) via passage (b), moving spool i
(5) to the left so that orifice (B) is widened. Therefore,
8
the return oil from the rod side can flow out via pas- 3
sage (d) to the hydraulic oil tank. 2
h
A

e C

b 6
9
d B
a

1
T111-02-05-035

PR PB
8 9

A
h

f e a i d
e
7 B
d
c

T111-02-05-029
6 5 4

1 - Arm Cylinder 4 - Piston 6 - Spring 8 - Holding Valve

2 - Spool 5 - Spool 7 - Arm Regenerative Valve 9 - Load Check Valve
3 - Check Valve

T3-3-19
 COMPONENT OPERATION / Control Valve
BOOM OVERLOAD RELIEF PRESSURE
SWITCH VALVE
The boom overload relief pressure switch valve is pro-
vided at the output port to the boom cylinders. The
boom overload relief pressure switch valve is oper-
ated by the pilot oil pressure from boom mode selec-
tion solenoid valve (SC) so that the overload relief
valve set pressure in the boom cylinder rod side is
reduced.
Normally, pressure oil in port HP is routed to chamber
(c) via piston (6), closing main poppet (5). Therefore,
the overload relief valve set-pressure is maintained.
When the pilot oil pressure from boom mode selection
solenoid valve (SC) is routed to piston (1), piston (1)
unseats poppet (2). When poppet (2) is unseated,
chamber (a) and (b) are connected to port LP via pas-
sage (d). When pressure at chamber (c) increases up
to set-force of spring (3), pilot poppet (4) is unseated,
reducing pressure in chamber (c) so that piston (6)
and main poppet (5) are moved to the left. Thereby,
main poppet (5) is unseated, allowing pressure oil to
directly flow to port LP from port HP. Consequently,
the overload relief valve set-pressure is reduced.

(Refer to the SYSTEM/Control System group)

T3-3-20
 COMPONENT OPERATION / Control Valve

1 2 a 3 4 5 6

Pilot
Pressure HP

LP
d b c
T183-03-03-018C

1 2 a 3 4 5 6

Pilot
Pressure HP

LP
b c
T183-03-03-019C

1 2 a 3 4 5 6

Pilot
Pressure HP

b
LP
T183-03-03-020C

1 - Piston 3 - Spring 5 - Main Poppet 6 - Piston

2 - Poppet 4 - Pilot Poppet

T3-3-21
 COMPONENT OPERATION / Control Valve
(Blank)

T3-3-22
 COMPONENT OPERATION / Pilot Valve
OUTLINE

The pilot valve functions to control pilot pressure oil, The pilot valves have the same mechanism to the
causing the control valve spools to move. reducing valve, except the mechanism of the cam part
The two types of 4-port pilot valves are used for the which press the pusher between the pilot valves for
front swing operations and travel operations as a front swing/travel operations and bucket operations.
standard. The 2-port pilot valve is used for the bucket
opens/closes operations (loading shovel only).
Bucket Open / Close Pilot Valve
Front / Swing Pilot Valve Travel Pilot Valve
(Only for Loading Shovel)

T
T
P
P

3 4
1

4 1 2
T183-03-04-001

2
2 1
P
3 T178-03-04-001C T178-03-04-002C

• Front/Swing Pilot Valve • Travel Pilot Valve

Right 1 Travel Left Forward
H (Hitachi)
Port # ISO Lever Type 2 Travel Left Reverse
Pattern

Common to 1 Bucket Roll-Out ← 3 Travel Right Reverse

Backhoe and 2 Boom Lower ← 4 Travel Right Forward
Loading 3 Bucket Roll-In ←
Shovel 4 Boom Raise ← • Bucket Open/Close Pilot Valve
Left (Only for Loading Shovel)
H (Hitachi) Left 1 Bucket Close
Port # ISO Lever Type
Pattern Right 2 Bucket Open
1 Arm Roll-In Swing Left
2 Swing Right Arm Roll-In
Backhoe
3 Arm Roll-Out Swing Right
4 Swing Left Arm Roll-Out
1 Arm Roll-In Swing Left
Loading 2 Swing Right Arm Roll-Out
Shovel 3 Arm Roll-Out Swing Right
4 Swing Left Arm Roll-In

T3-4-1
 COMPONENT OPERATION / Pilot Valve
OPERATION
Spool (6) head comes in contact with the upper face
of spring guide (3) which is kept raised by return
spring (5).

NOTE: The pilot valve for bucket open/close has

the same internal structure as the pilot
valve for travel.
Refer to the movement of the pilot valve
for travel.

Neutral (Output Diagram: A to B):

1. When neutral, spool (6) totally blocks pressure oil
E F
port P (from the pilot pump).The output port is
opened to port T (hydraulic oil tank) through the
passage in spool (6). Therefore, oil pressure in D
the output port (to the control valve) is equal to Pilot
that in port T. Pressure
2. When the control lever is slightly tilted, cam (1) is
tilted, moving pusher (2) downward. Then, C
pusher (2) compress return spring (5) along with
spring guide (3). At this time, as oil pressure in
A B
the output port is equal to that in port T, spool (6) Lever Stroke
moves downward while keeping the under face of T522-02-05-001

the spool head in contact with spring guide (3).

3. This status continues until hole (7) on spool (6) is
opened to port P.

T3-4-2
 COMPONENT OPERATION / Pilot Valve
Front Attachment / Swing Pilot Valve

1 1

2 2

6
3 3 Port T

4 4
7

5 5 Port P

6 Output Port
6

Port T Port T

7 Port P 7 Port P

Output Port T183-03-04-002

Output Port T183-03-04-004

Travel Pilot Valve

1 1

2 2 Port T

Port P
3 3 6

4 4

5 Output Port
5
6
Port T Port T

6
Port P Port P
7 7

Output Port T183-03-04-003

Output Port T183-03-04-005

1 - Cam 3 - Spring Guide 5 - Return Spring 7 - Hole

2 - Pusher 4 - Balance Spring 6 - Spool

T3-4-3
 COMPONENT OPERATION / Pilot Valve
During Metering or Decompressing (Output
Diagram: C to D)
1. When the control lever is further tilted to move E F
pusher (2) downward more, hole (7) on spool (6)
is opened to port P, allowing pressure oil in port P
D
to flow into the output port.
Pilot
2. Oil pressure in the output port acts on the bottom Pressure
face of spool (6) so that spool (6) is pushed
upward.
C
3. However, until upward force acting on the bottom
face of spool (6) overcomes balance spring (4)
force, balance spring (4) is not compressed. A B
Lever Stroke
Then, spool (6) is not raised, allowing oil
pressure in the output port to increase. T522-02-05-001

4. As oil pressure in the output port increases, force

to push spool (6) upward increases. When, this
force overcomes balance spring (4) force,
balance spring (4) is compressed so that spool
(6) is moved upward.
5. As spool (6) is moved upward, hole (7) is closed
so that pressure oil from port P stops flowing into
the output port, stopping pressure oil in the
output port to increase.
6. As spool (6) is moved downward, balance spring
(4) is compressed, increasing the spring force.
Therefore, oil pressure in the output port
becomes equal to the oil pressure acting on the
bottom face of spool (6) being balanced in
position with the spring force.

T3-4-4
 COMPONENT OPERATION / Pilot Valve
Front Attachment / Swing Pilot Valve

1 1

2 2

3 3

4 4

5 5

6 6

Port T Port T

7 Port P 7 Port P

Output Port T183-03-04-006

Output Port T183-03-04-008

Travel Pilot Valve

1 1

2 2

3 3

4 4

5 5

6 6
Port T Port T

Port P Port P
7 7

Output Port Output Port T183-03-04-009

T183-03-04-007

1 - Cam 3 - Spring Guide 5 - Return Spring 7 - Hole

2 - Pusher 4 - Balance Spring 6 - Spool

T3-4-5
 COMPONENT OPERATION / Pilot Valve
Full Stroke (Output Diagram: E to F)
1. When the control lever is fully stroked, pusher (2)
is moved downward until pusher (2) in the front E F
attachment / swing pilot valve comes in contact
with the casing shoulder, or cam (1) on the travel
D
pilot valve comes in contact with the casing. Pilot
2. At this moment, the bottom of pusher (2) directly Pressure
pushes spool (6). Therefore, even if oil pressure
in the output port increases further, hole (7) on
C
spool (6) is kept open.
3. Consequently, oil pressure in the output port is
equal to oil pressure in port P. A B
Lever Stroke
T522-02-05-001

NOTE: Total lever strokes for the front attachment

and swing controls are determined by
stroke dimension (E) of pusher (2). Total
lever stroke for the travel control is
determined by stroke dimension (E) of cam
(1).

T3-4-6
 COMPONENT OPERATION / Pilot Valve

Front Attachment / Swing Pilot Valve

2 2

4
5

Port T

7 Port P

Output Port T183-03-04-010

T183-03-04-002

Travel Pilot Valve

1
1

E
2

6
Port T

Port P
7

T183-03-04-003
Output Port T183-03-04-011

1 - Cam 3 - Spring Guide 5 - Return Spring 7 - Hole

2 - Pusher 4 - Balance Spring 6 - Spool

T3-4-7
 COMPONENT OPERATION / Pilot Valve
(Blank)

T3-4-8
 COMPONENT OPERATION / Travel Device
OUTLINE
The travel device consists of a travel motor (12),
planetary reduction gear (1) to (11), (13) and sprocket
(14).

3
2

7
8
9

10

11

12

14

13

T183-03-01-001

1- Third Stage Carrier 5- Ring Gear 9 - Second Stage Carrier 12 - Travel Motor
2- Third Stage Sun Gear 6- Shaft 10 - Third Stage Planetary Gear 13 - Drum
3- Second Stage Planetary Gear 7- First Stage Carrier 11 - Housing 14 - Sprocket
4- First Stage Planetary Gear 8- Second Stage Sun Gear

T3-5-1
 COMPONENT OPERATION / Travel Device
TRAVEL REDUCTION GEAR
The travel reduction gear is a three stage planetary As third stage carrier (2) is held stationary with
gear. When the travel motor rotates clockwise, shaft housing (11), ring gear (1) rotates.
(6) rotates clockwise, transmitting this motor driving Ring gear (1) is bolted to drum (13) so that sprocket
power to ring gear (1) via first stage planetary gears (12) is rotated.
(8), first stage carrier (5), second stage sun gear (7),
second stage planetary gears (9), second stage car-
rier (4), third stage sun gear (3), third stage planetary
gears (10) and third stage carrier (2).

11 12 13 1

2
3
4

6
7

Third Second First

Stage Stage Stage

10 9

T183-03-05-002

1- Ring Gear 5 - First Stage Carrier 8 - First Stage Planetary Gear 11 - Housing (Travel Motor)
2- Third Stage Carrier 6 - Shaft 9 - Second Stage Planetary Gear 12 - Sprocket
3- Third Stage Sun Gear 7 - Second Stage Sun Gear 10 - Third Stage Planetary Gear 13 - Drum
4- Second Stage Carrier

T3-5-2
 COMPONENT OPERATION / Travel Device
TRAVEL MOTOR
The travel motor is a variable displacement swash Four of tilt piston (9) are located in casing (8). The
plate axial plunger type, consisting of swash plate (7), pressure to change travel speed acts on these tilt
rotor (16), plungers (4) with shoes, valve plate (1), pistons (9) to change swash plate (7) angle.
output shaft (11), tilt pistons (9), casing (8), and so Rotor (16) is preloaded against valve plate (1) by
forth. spring (14) to prevent oil from leaking at the clear-
ance between them.
Hydraulically released type disc parking brake (3) is
installed in the travel motor.

1 2 3 4 5 6 7 8 9 10

11

17

16

T183-03-05-003

15 14 13 12

1- Valve Plate 6- Retainer Plate 10 - Spring 14 - Spring

2- Spring 7- Swash Plate 11 - Output Shaft 15 - Brake Piston
3- Parking Brake 8- Casing 12 - Roller Bearing 16 - Rotor
4- Plunger 9- Tilt Piston 13 - Ball 17 - Valve Cover
5- Holder

T3-5-3
 COMPONENT OPERATION / Travel Device
Pressure oil from the pump flows to port A of valve As output shaft (6) rotates, rotor (2) also rotates. Then,
plate (1), and enters into one-sided bores in rotor (2) when plungers (3) reach port B, oil is routed to the
located just behind the right-side crescent-shaped oil hydraulic oil tank.
port (port A side) of valve plate (1). Whether pressure oil from the pump is supplied to
Then, plungers in the right half side of rotor (2) are port A or port B determines the travel direction.
pushed out toward swash plate (5), and slide on the
swash plate to rotate rotor (2) and output shaft (6).

Port B Port A
Port B
Port A

1
2

4
6 5
Valve Plate
T183-03-05-009C

1 - Valve Plate 3 - Plunger 5 - Swash Plate 6 - Output Shaft

2 - Rotor 4 - Shoe

T3-5-4
 COMPONENT OPERATION / Travel Device
TRAVEL BRAKE VALVE
The travel brake valve is located on the travel motor
head and consists of the following valves:

Counterbalance Valve: Check Valve:

ensures smooth starts and stops and prevents ensures smooth starts and stops, and prevents
overrunning when traveling down slopes. cavitation from occurring in the motor circuit by
Overload Relief Valve: functioning together with counterbalance valve.
prevents overloads and surge pressure in the Travel Speed Shift Valve:
motor circuit. controls the tilt pistons when travel mode switch
is operated.

Cross Section A-A-A

Overload Relief Counterbalance
Valve Valve

Travel Speed
Shift Valve

Check Valve

A A A
Overload Relief Counterbalance
Valve Valve
T183-03-05-004C

T3-5-5
 COMPONENT OPERATION / Travel Device
Travel Operation
When supply oil from the main control valve is routed
to port P1, supply oil flows around spool CB, opens
check valve BC and is led to motor port BM. How-
ever, return oil from motor port AM is blocked by
spool CB in the counterbalance valve.
As supply oil pressure at port P1 increases, supply
oil is routed to chamber G through orifice F in spool
CB, moving spool CB down against spring force.
Consequently, return oil from motor port AM starts to
flow into port P2 through notch H in spool CB, allow-
ing the travel motor to rotate.

When the travel levers are returned to the neutral

position, the oil in both ports P1 and P2 are routed to
the hydraulic oil tank through the control valve. Thus,
oil pressure in chamber G decrease, and spool CB is
moved back to the original position by spring force.
Then, the oil flow circuits is blocked, causing the
travel motors to stop rotating.

Descending Operation
When the machine travels down a slope, the travel
motors are forcibly driven by the machine weight so
that the motor draws oil like a pump. When the motor
draws oil, oil pressure at port P1 and chamber G de-
crease, causing spool CB to move upwards to re-
strict return circuit from the motor.
Then, the return oil flow from the motor is restricted
by the spool, increasing pressure at port AM.
The increased pressure at port AM brakes the motor.
Thus, the restricted return oil flow from the travel
motor increases the pressure at port P1 again, mov-
ing spool CB back down. This repeated movement of
the spool (hydraulic brake action) prevents the ma-
chine from overrunning.

T3-5-6
 COMPONENT OPERATION / Travel Device
(Travel Operation) Check Valve
BM BC G Spool CB

Spool CB

F
P1

P1
To BM

P2
P2
From AM

AM Counterbalance Valve

T183-03-05-005C

(Descending Operation)
BM G Spool CB
G

Spool CB

P1

P1
To BM

P2
P2

From AM

AM

T183-03-05-006C

T3-5-7
 COMPONENT OPERATION / Travel Device
Circuit Protection
If pressure in the circuit increases over the setting
pressure of the overload relief valve, this valve Overload Re-
lief Valve
opens to relieve peak pressure to the lower pressure
side to protect the motor from overloading. This
valve also functions to release shock pressure
caused by inertia force developed when the motor
stops.

Poppet

Low Pressure

High Pressure
T183-03-05-011C

T3-5-8
 COMPONENT OPERATION / Travel Device
(Blank)

T3-5-9
 COMPONENT OPERATION / Travel Device
TRAVEL MOTOR DISPLACEMENT ANGLE
CHANGE
The travel speed mode changes as the displacement
angle of swash plate (3) is changed by tilt piston (5).

• Slow Speed Travel

(Maximum Displacement Angle)
While pilot pressure (7) that pressure is reduced by With the above, the swash plate (3) displacement an-
the signal pressure from the travel 2nd speed shift gle is fixed to the large side, and thus the plunger (6)
solenoid valve is supplied to travel speed shift valve stroke becomes maximum. Accordingly, the amount of
(1), spool A (8) is held in neutral by spring (2), oil required to rotate the travel motor (per turn) be-
blocking pressure oil from the control valve. Pilot comes maximum, resulting in slow speed travel motor
pressure (7) is routed to the parking brake through operation.
the passage of spool A (8) via the circumference (Refer to the Control System Group in the SYSTEM
clearance of spool B (9) to release the parking Section for the control circuit.)
brake. At the same time, the line to tilt pistons (5) is
opened to the hydraulic oil tank line 9 7 8 1 2
Travel Speed Shift Valve

5 6

To Hydraulic Oil Tank

Parking Brake

4 3

From Control
Valve T183-03-05-007C

1 - Travel Speed Shift Valve 4 - Ball 6 - Plunger 8 - Spool A

2 - Spring 5 - Tilt Piston 7 - Pilot Pressure (from Reducing Valve) 9 - Spool B
3 - Swash Plate

T3-5-10
 COMPONENT OPERATION / Travel Device
• Fast Speed Travel
(Minimum Displacement Angle)
While non-pressure-reduced pilot pressure (7) is Tilt pistons (5) push swash plate (3), changing the dis-
supplied to travel speed shift valve (1), pilot pres- placement angle to the minimum, resulting in the fast
sure (7) is supplied to chamber (a) via the circum- speed travel motor operation.
ference clearance of spool B (9), shifting spool A (8) (Refer to the Control System Group in the SYSTEM
to the right. Also, the pilot pressure (7) is supplied to Section for the control circuit.)
the parking brake via chamber (b) in spool A (8) to
release the parking brake. By the movement of
spool A (8), pressure oil from the control valve ex-
erts on tilt pistons (5).

9 a 7 b 8 1 2
Travel Speed Shift Valve
5 6

From Travel
Speed Shift Valve

Parking Brake

4 3

From Control
Valve
T183-03-05-008C

1 - Travel Speed Shift Valve 4 - Ball 6 - Plunger 8 - Spool A

2 - Spring 5 - Tilt Piston 7 - Pilot Pressure (from Reducing Valve) 9 - Spool B
3 - Swash Plate

T3-5-11
 COMPONENT OPERATION / Travel Device
PARKING BRAKE
The parking brake is a negative-type brake released The friction plates are connected to the rotor, and the
when pilot oil pressure is applied to parking brake plates to the casing via spline couplings respectively.
chamber M. Whenever the travel control valve spools When the spring pushes the piston to the right, the
are in neutral, the parking brake is automatically ap- friction plates come into contact with the plates, ap-
plied. plying the parking brake.
(Refer to the pilot circuit diagram in the Hydraulic Cir-
cuit Group, the SYSTEM Section, for pilot oil flow.)

Spring Piston Plate

M
Friction Plate
Casing

Rotor
T183-03-05-003

T3-5-12
 COMPONENT OPERATION / Travel Device
Brake ON Spring
When the control lever is in the neutral position, the
friction plates and plates are pressed down by spring
force, braking the motor. Pressure oil in brake cham-
ber M is released to the hydraulic oil tank.

Spring

Plate

Friction Plate

Casing
Rotor
T111-03-04-007C

Brake OFF Spring

When the control lever is operated, pilot oil is led to
brake chamber M and pushes the brake piston
against spring force. Consequently, the friction plates M
are separated from the plates, releasing the parking
brake.

Spring

Plate

Friction Plate

Casing
Rotor
T111-03-04-008C

T3-5-13
 COMPONENT OPERATION / Travel Device
(Blank)

T3-5-14
 COMPONENT OPERATION / Signal Control Valve
OUTLINE
The signal control valve is provided in the pilot circuit
between the pilot valve and the control valve, and
controls pilot signal pressure used to regulate the
pumps and various kinds of valves.
The signal control valve consists of shuttle valves,
shockless valve, pump 1 and 2 flow rate control valve,
flow combiner valve control spool, arm flow rate con-
trol valve and priority valve.

Pilot Valve
Side

T178-03-06-016CC
Cross Section A-A

Shockless Valve

Arm Flow Rate Control Auxiliary

Pump 1 and 2 Flow Rate Control Valve Auxiliary

Flow Combiner Valve

Priority Valve Control Spool

T178-03-06-002C

T3-6-1
 COMPONENT OPERATION / Signal Control Valve
PILOT PORT

NOTE: BH: Backhoe

LD: Loading Shovel
Pilot Valve Side
Port Name Connecting to Note
Port A Right Pilot Valve Boom Raise Pilot Pressure
Port B Right Pilot Valve Boom Lower, Bucket Roll-Out Pilot Pres-
sure
Port C Left Pilot Valve Arm Roll-Out Pilot Pressure (BH)
Arm Roll-In Pilot Pressure (LD)
Port D Right Pilot Valve Boom Raise Pilot Pressure
Port E Hydraulic Oil Tank Returning to Hydraulic Oil Tank
Port F Left Pilot Valve Arm Roll-Out Pilot Pressure (BH)
Arm Roll-In Pilot Pressure (LD)
Port G Left Pilot Valve Arm Roll-In Pilot Pressure (BH)
Arm Roll-Out Pilot Pressure (LD)
Port H Right Pilot Valve Bucket Roll-In Pilot Pressure
Port I Travel Pilot Valve Left Travel Reverse Pilot Pressure
Port J Travel Pilot Valve Left Travel Forward Pilot Pressure
Port K Travel Pilot Valve Right Travel Reverse Pilot Pressure
Port L Travel Pilot Valve Right Travel Forward Pilot Pressure
Port M Auxiliary Pilot Valve (BH) Auxiliary Pilot Valve (BH)
Bucket Open Pilot Valve (LD) Bucket Open Pilot Valve (LD)
Port N Auxiliary Pilot Valve (BH) Auxiliary Pilot Valve (BH)
Bucket Open Pilot Valve (LD) Bucket Open Pilot Valve (LD)
Port SA Pump 1 and 2 Regulator Pump 1 and 2 Control Pressure
Port SB − Plug
Port PI Pilot Shut-Off Valve Primary Pilot Pressure
Port PH Pilot Shut-Off Valve Primary Pilot Pressure (Heat Circuit)
Port SH − Plug
Port DF Hydraulic Oil Tank Returning to Hydraulic Oil Tank

T3-6-2
 COMPONENT OPERATION / Signal Control Valve

Pilot Valve Connecting Side

PH
C
A

E
M
D

H
B
F
SB

PI G

Pilot Valve
Side

K N

I
SH
J

DF

SA L
T178-03-06-016CC

T3-6-3
 COMPONENT OPERATION / Signal Control Valve

NOTE: BH: Backhoe

LD: Loading Shovel
Control Valve Side
Port Name Connecting to Note
Port 1 Control Valve Boom Raise Pilot Pressure
Port 2 − Plug
Port 3 − Plug
Port 4 − Plug
Port 5 − Plug
Port 6 Control Valve Arm Roll-Out Pilot Pressure (BH)
Arm Roll-In Pilot Pressure (LD)
Port 7 Control Valve Arm Roll-In Pilot Pressure (BH)
Arm Roll-Out Pilot Pressure (LD)
Port 8 Control Valve Bucket Roll-In Pilot Pressure
Port 9 Control Valve Left Travel Reverse Pilot Pressure
Port 10 Control Valve Left Travel Forward Pilot Pressure
Port 11 Control Valve Right Travel Reverse Pilot Pressure
Port 12 Control Valve Right Travel Forward Pilot Pressure
Port 13 Control Valve Auxiliary Close Pilot Pressure (BH)
Bucket Close Pilot Pressure (LD)
Port 14 Control Valve Auxiliary Open Pilot Pressure (BH)
Bucket Open Pilot Pressure (LD)
Port SE Shuttle Valve Boom Raise Priority Pilot Pressure
Port SM Shuttle Valve Auxiliary
Port SN Shuttle Valve Swing Brake Release
Port SP Shuttle Valve Swing Brake Release
Port SL Control Valve Combiner Valve Shifting Pressure
Port SK − Plug

T3-6-4
 COMPONENT OPERATION / Signal Control Valve

Control Valve Connecting Side

SM
3

1 5

13

2 4
SK
SE

S3 8

14
Control Valve 7
Side
9
6
10

SN
SL

11

Pressure Sensor (Travel) 12 SP T178-03-06-015C

T3-6-5
 COMPONENT OPERATION / Signal Control Valve
SHUTTLE VALVE

NOTE: BH: Backhoe

LD: Loading Shovel
The shuttle valve selects the pilot pressure oil used to
perform each operation and routes it to the corre-
sponding flow rate control valves and/or switch valve
spools. The flow rate control valves and/or switch
valve spools corresponding to each operation are as
follows:

Pump 1 and 2 Flow Arm Flow Rate Flow Combiner Priority Valve
Control Valve Control Valve Valve
Control Spool
Boom Raise { { − {
Boom Lower { − − {
Arm Roll-Out (BH)
{ − − {
Arm Roll-In (LD)
Arm Roll-In (BH)
{ − − {
Arm Roll-Out (LD)
Bucket Roll-In { − − {
Bucket Roll-Out { − − {
Right Travel { − { −
Left Travel − − − −
Auxiliary (Close) (BH)
− − − {
Bucket Close (LD)
Auxiliary (Open) (BH)
− − − {
Bucket Open (LD)

T3-6-6
 COMPONENT OPERATION / Signal Control Valve

Swing Arm Boom Bucket Left Travel Right Travel

1 2 3 4 5

Shockless Valve

6
Arm Flow Rate Control
Valve
P1 and P2 Pump Flow
Rate Control Valve
Flow Combiner Valve
Control Spool
Priority Valve

T183-03-06-001

17 16 15 14 13 12 11 10 9 8 7

1 - Auxiliary (BH), Bucket 6 - Right Travel 10 - Boom Raise, Arm Roll-Out 14 - Boom, Arm, Bucket
Open/Close (LD) (BH), Arm Roll-In (LD), Auxil-
iary (BH), Bucket Open/Close
(LD), Left Travel
2 - Arm Roll-Out (BH), Arm Roll-In 7 - Left Travel, Right 11 - Boom, Arm, Bucket, Right 15 - Boom Raise, Arm Roll-Out
(LD), Auxiliary (BH), Bucket Travel Travel (BH), Arm Roll-In (LD)
Open/Close (LD)
3 - Arm Roll-Out (BH), Arm Roll-In 8 - Boom, Arm, 12 - Arm Roll-In (BH), Arm 16 - Boom Raise, Arm. Roll-Out
(LD) Bucket, Right Roll-Out (LD), Bucket Roll-In (BH), Arm Roll-In (LD)
Travel
4 - Boom, Bucket Roll-Out 9 - Left Travel 13 - Room Raise, Arm, Bucket 17 - Boom Raise, Arm. Roll-Out
(BH), Arm Roll-In (LD), Aux-
iliary (BH), Bucket
Open/Close (LD)
5 - Boom, Arm Roll-Out (BH), Arm
Roll-In (LD), Bucket Roll-Out

NOTE: BH: Backhoe

LD: Loading Shovel

T3-6-7
 COMPONENT OPERATION / Signal Control Valve

Swing Arm Boom Bucket Left Travel Right Travel

1 2 3 4 5

Shockless Valve

6
Arm Flow Rate
Control Valve
P1 and P2 Pump Flow
Rate Control Valve
Flow Combiner Valve
Control Spool
Priority Valve

T183-03-06-001

17 16 15 14 13 12 11 10 9 8 7

NOTE: BH: Backhoe

LD: Loading Shovel

T3-6-8
 COMPONENT OPERATION / Signal Control Valve

Pilot Valve
Side

T178-03-06-016CC

Cross Section B-B

5
8
7

16

17

15
13
11
14

6 10

12
3
1
4

2
T178-03-06-009C

1 - Auxiliary (BH), Bucket 6 - Right Travel 10 - Boom Raise, Arm Roll-Out 14 - Boom, Arm, Bucket
Open/Close (LD) (BH), Arm Roll-In (LD), Auxil-
iary (BH), Bucket Open/Close
(LD), Left Travel
2 - Arm Roll-Out (BH), Arm Roll-In 7 - Left Travel, Right 11 - Boom, Arm, Bucket, Right 15 - Boom Raise, Arm Roll-Out
(LD), Auxiliary (BH), Bucket Travel Travel (BH), Arm Roll-In (LD)
Open/Close (LD)
3 - Arm Roll-Out (BH), Arm Roll-In 8 - Boom, Arm, 12 - Arm Roll-In (BH), Arm 16 - Boom Raise, Arm Roll-Out
(LD) Bucket, Right Roll-Out (LD), Bucket Roll-In (BH), Arm Roll-In (LD)
Travel
4 - Boom, Bucket Roll-Out 9 - Left Travel 13 - Room Raise, Arm, Bucket 17 - Boom Raise, Arm Roll-Out
(BH), Arm Roll-In (LD), Aux-
iliary (BH), Bucket
Open/Close (LD)
5 - Boom, Arm Roll-Out (BH), Arm
Roll-In (LD), Bucket Roll-Out

T3-6-9
 COMPONENT OPERATION / Signal Control Valve
SHOCKLESS VALVE Detail of C

The shockless valve is provided in the boom raise

circuit and functions during boom lowering operation.

During Boom Raising Operation:

1. Boom raise pilot pressure oil is routed into port A
and acts on the spool.
2. Immediately after operation is started, the low pi-
lot pressure oil flows to port 1 via clearance C
T183-03-06-002
between the spool and the housing, and inner Pilot Valve Side
passage 2. Inner Passage 1 Port A C Spool
3. The set-force of spring A is weaker than that of Spring B
spring B. Therefore, when the pilot pressure in-
creases, the spool is moved to the left.
4. As the spool is moved to the left, port A is con-
nected to port 1, increasing pressure in port 1 so
that the spools of the boom 1 and 2 in the main
control valve is moved.

Inner Pas- Oil Chamber

Port 1 sage 2
Spring A T178-03-06-013C

Control Valve Side

T3-6-10
 COMPONENT OPERATION / Signal Control Valve

During Boom Raising Operation: Boom Raise Pilot Pressure

Spool Port A

Inner Passage 2
Spring B
Spring A

Port 1 T183-03-06-003C

Boom Raise Pilot Pressure

Spool Port A

Port 1 T183-03-06-004C

to Spools of Boom 1 and 2 in Main

Control Valve

T3-6-11
 COMPONENT OPERATION / Signal Control Valve
During Boom Lowering Operation (Shock Re- Detail of C
ducing Operation)
1. When the boom is lowered, the return oil from the
boom raise spools of the boom 1 and 2 in the
main control valve is routed to port 1.
2. Since the spool blocks the oil passage between
port 1 and port A, the return oil cannot flow di-
rectly to port A.
3. Port 1 is connected to spring A side via inner
passage 1 and to the oil chamber via inner pas-
T183-03-06-002
sage 2. Pilot Valve Side
4. Pressure oil in the oil chamber flows out from Inner Passage 1 Port A C Spool
clearance C between the spool and the housing, Spring B
reducing pressure in the oil chamber. Then, the
spool is moved to the right by pressure in the
spring A side. Thereby, clearance C between the
spool and the housing is closed, blocking pres-
sure oil flow.
5. When clearance C is closed, pressure in the oil
chamber increases, moving the spool to the left.
Therefore, clearance C is opened again allowing
pressure oil to flow to port A.
6. As operation in steps (4 and 5) are repeated,
pressure oil is gradually returned to port A so that
the spools of the boom 1 and 2 in the main con-
trol valve returns slowly.
Inner Passage Oil Chamber
Port 1 2
Spring A T178-03-06-013C

Control Valve Side

T3-6-12
 COMPONENT OPERATION / Signal Control Valve
During Boom Lowering Operation (Shock Reducing Operation)

Inner Passage 1
to Pilot Valve
Spring A Spool Port A

Inner Passage 2 Oil Chamber

Port 1 T183-03-06-003C
from Spools of Boom 1 and 2 in
Main Control Valve
Inner Passage 1 Spool
Port A

Inner Passage 2 Oil Chamber

Port 1 T183-03-06-005C
Spring A from Spools of Boom 1 and 2 in
Main Control Valve
Spool to Pilot Valve
Port A

Inner Passage 2 Oil Chamber

Port 1 T183-03-06-004C
from Spools of Boom 1 and 2 in
Main Control Valve

T3-6-13
 COMPONENT OPERATION / Signal Control Valve
PUMP 1 AND 2 FLOW RATE CONTROL
VALVE
The pump flow rate control valve delivers pump con-
trol pressure Pi to the pump regulator in response to
the pilot oil pressure from the pilot valve, and controls
the swash angle of the pump 1 and 2 to deliver the
flow rate required by the control lever.

1. Pilot oil pressure from the pilot valve in the travel

and front operation system is routed into the
spring chamber side of the pump 1 and 2 flow
rate control valve after being selected by the
shuttle valves in the signal pilot pressure control
valve.
2. Then, the spool is moved to the right, causing the
primary pilot pressure to flow in port SA.
3. Therefore, pressure in port SA increases.
4. Oil pressure in port SA acts on the right end of
the spool. Thus, the spool is moved back to the
left until pressure force in port SA is balanced
with pilot pressure force in the spring chamber so
that pressure in port SA stops increasing. In other
words, the primary pilot pressure is reduced to
the pressure which is corresponding to the pilot
pressure from the pilot valve, and deliver the
pressure as Pi pressure to the regulators in pump
1 and 2 from port SA.

T3-6-14
COMPONENT OPERATION / Signal Control Valve

Port SA
Spring Spool

Primary Pilot Pressure

Pilot Pressure

Shuttle Valve

T178-03-06-017C

T3-6-15
 COMPONENT OPERATION / Signal Control Valve
ARM FLOW RATE CONTROL VALVE,
FLOW COMBINER VALVE CONTROL
SPOOL, PRIORITY VALVE

NOTE: The three captioned spools are indicated

in operational principle. Arm Flow Rate Control Valve:
BH: Backhoe
LD: Loading Shovel Arm Roll-Out
(BH) / Arm
To Hydraulic Roll-In (LD) Pi-
The arm flow rate control valve delivers the arm Oil Tank lot Pressure
roll-out (BH)/arm roll-in (LD) pilot pressure to the Spool Spring
roll-in (BH)/roll-out (LD) side of the arm 2 spool in the
main control valve by shifting the spool using boom
raise pilot pressure.

T178-03-06-014C
Boom Raise To Arm 2 Spool Roll-In
Pilot Pressure Side (BH) / Roll-Out
Side (LD)

The flow combiner valve control spool delivers the pi- Flow Combiner Valve Control Spool:
lot pressure to the flow combiner valve in the main
control valve from the priority valve by shifting the To Hydraulic Pilot Pressure from
Oil Tank Priority Valve
spool using right travel pilot pressure.
Spool Spring

T178-03-06-014C
Right Travel To Flow Combiner
Pilot Pressure Valve

The priority valve delivers the primary pilot pressure to

Priority Valve:
flow combiner valve control spool by shifting the spool
using boom, arm, bucket and auxiliary (BH)/bucket To Hydraulic Primary Pilot
open/close (LD) pilot pressure. Oil Tank Pressure
Spool Spring

T178-03-06-014C
Boom, Arm, To Flow Combiner
Bucket, Auxiliary Valve Control Spool
(BH) / Bucket
Open/Close (LD)
Pilot Pressure

T3-6-16
 COMPONENT OPERATION / Others (Upperstructure)
PILOT SHUT-OFF VALVE

The pilot shut-off valve is a manually operated switch

valve. The valve spool is rotated when the pilot control
shut-off lever is operated, switching ON and OFF the
pilot pressure oil to the pilot valve. Cross Section Z-Z

Operation with Pilot Control Shut-Off Lever in

LOCK Position

When the pilot control shut-off lever is in the LOCK

position, the pilot shut-off valve is set in neutral
(OFF), blocking pilot pressure oil from the pilot pump
to enter the pilot valves. Pressure oil is routed to the
signal control valve via port A5. Pilot pressure oil on
the pilot valve side is routed to the hydraulic tank via
port T4. As a result, the pilot valve becomes
inoperable with the control levers.
T178-03-07-002C
A5 Port P Port
Operation with Pilot Control Shut-Off Lever in from Pilot
to Signal Control
UNLOCK Position Valve Pump

When the pilot control shut-off lever is moved to the

UNLOCK position, the pilot shut-off valve is turned
to the ON position, blocking the line to the tank from
the pilot valve and, at the same time, routing the
pilot pressure oil from the pilot pump to the pilot
valves via ports A1, A2 and A3. Thus, the pilot valves
become operable with the control levers.
A2 A1
Z

T1 T2 A3 A4 T4

T3 P

A5 T178-03-07-003C

A1 - Travel Pilot Valve A4 - Signal Control Valve (Port PI) T1 - Travel Pilot Valve T4 - Hydraulic Oil Tank
A2 - Left Pilot Valve A5 - Signal Control Valve (Port PH) T2 - Left Pilot Valve
A3 - Right Pilot Valve P - Primary Pilot Pressure T3 - Right Pilot Valve

T3-7-1
 COMPONENT OPERATION / Others (Upperstructure)
SHOCKLESS VALVE To Boom Lower Spool and
Holding Valve Control
Valve Plunger
The shockless valve is located in the boom lower pilot A
operation circuit and pump 2 regulator Pi pressure
circuit. The shockless valve in the boom lower pilot
operation circuit controls boom lower pilot pressure
and the flow of the holding valve control valve for
boom lowering to cushion abrupt movement at the
boom lower spool and holding valve control valve.
The shockless valve of the pump 2 regulator Pi
pressure circuit controls the flow between port Pi of
the regulator in the pump 2 and the pilot valve at the
swing stopping operation to prevent rapidly decrease
of the delivery amount from pump 2.
(Refer to the Hydraulic Pressure System Group in the
SYSTEM Section for the swing motor make-up
circuit.)
B Orifice
T183-03-07-008C
From Pilot Valve

To Boom Lower Spool and

Shockless Valve in Boom Lower Pilot Operation Holding Valve Control Valve
Circuit Plunger
A
• When a control lever is operated, the pilot valve
routes the pilot pressure to port B of the shockless
valve. Just after the control lever operation, the pilot
pressure oil flows to Port A through the shockless
valve only via orifice of the plunger. When pressure
from the pilot valve increases further, the plunger
move to the left, so that hydraulic oil volume
increases.

B
T183-03-07-009C
From Pilot Valve

T3-7-2
 COMPONENT OPERATION / Others (Upperstructure)
• Return oil from the boom lower spool in the control From Boom Lower Spool
and Holding Valve Control
valve and holding valve control valve is returned to Valve Plunger
the hydraulic oil tank via orifice. When the quantity A
of return oil increases, increasing the pressure in
the A side of the shockless valve, the plunger is
moved to the right in proportion to the pressure to
restrict the return oil.

B Orifice
T183-03-07-008C
To Hydraulic Oil Tank
via Pilot Valve

From Boom Lower Spool

and Holding Valve Control
Valve Plunger
A

B
T183-03-07-010C
To Hydraulic Oil Tank
via Pilot Valve

T3-7-3
 COMPONENT OPERATION / Others (Upperstructure)
To Port Pi of Regulator in
Shockless Valve in Pump 2 Regulator Pi Pump 2 Plunger
Pressure Circuit A

• When a control lever is operated, the pilot valve

routes the pilot pressure to port B of the shockless
valve. Just after the control lever operation, the pilot
pressure oil flows through the shockless valve only
via orifice. Then, it enters into Port A and act on the
port Pi of the regulator in the pump 2. When the
pressure increases further, the plunger move to the
left, so that hydraulic oil volume increases.

B Orifice
T183-03-07-008C
From Pilot Valve
To Port Pi of Regulator in
Pump 2 Plunger
A

B
T183-03-07-009C
From Pilot Valve

T3-7-4
 COMPONENT OPERATION / Others (Upperstructure)
• Return oil from port Pi of the regulator in the pump From Port Pi of Regulator
in Pump 2 Plunger
2 is returned to the hydraulic oil tank via orifice. A
When the quantity of return oil increases, increasing
the pressure in the A side of the shockless valve,
the plunger is moved to the right in proportion to the
pressure to restrict the return oil.

B Orifice
T183-03-07-008C
To Hydraulic Oil Tank
via Pilot Valve
From Port Pi of Regulator
in Pump 2 Plunger
A

B
T183-03-07-010C
To Hydraulic Oil Tank
via Pilot Valve

T3-7-5
 COMPONENT OPERATION / Others (Upperstructure)
SOLENOID VALVE Solenoid Valve Unit
Boom Mode Horsepower Horsepower
Solenoid Valve Unit Selection Reducing Reducing
Upon receiving signals from the main controller, the Solenoid Solenoid Solenoid
Valve Valve Valve
solenoid valve unit controls the main pump flow.
The solenoid vale unit consists of two horsepower
reducing solenoid valves (SA, SB), boom mode Pilot Relief Valve
SC SB SA
selection solenoid valve (SC) and pilot relief valve.
Solenoid Valve SA: Horsepower Reducing Solenoid
Valve: used for the main pump 3 oil flow control.
Solenoid Valve SB: Horsepower Reducing Solenoid
Valve: used for the main pump 1 and 2 oil flow
control.
Solenoid Valve SC: Boom Mode Selection Solenoid
Valve: used for the pilot pressure control of the
overload relief pressure switch valve.
(Refer to the Control System Group in the SYSTEM
Section for the pump control.)

T183-03-07-003

Spring Spool Solenoid

• Solenoid Valve Operation

In Neutral: The spool is pushed to the right
by the spring. Pilot pressure P
is blocked.
When Magnetized: The spool is pushed to the left
by the energized solenoid. Pilot
pressure P is connected to the
output port.
P Output T2 T111-02-07-003
Port Tank Port

Spool Spring

• Pilot Relief Valve Operation

The pilot relief valve sets the pilot pressure
delivered to the port P at a certain level.
The relief port T1 is connected to the heat circuit in
the shockless valve. T111-02-07-004
P T1

T3-7-6
 COMPONENT OPERATION / Others (Upperstructure)
Flow Rate Reducing Solenoid Valve
Upon receiving signals from the main controller A,
the flow reducing solenoid valve controls the main
pump 1 and 2 flow.
(Refer to the Control System Group in the SYSTEM
Section for the pump control.)

Travel Mode Solenoid Valve

Upon receiving signals from the main controller A,
the travel 2nd speed shift solenoid valve controls
Reducing Flow
the swash angle of the travel motor. Rate Solenoid
(Refer to the Control System Group in the Valve
SYSTEM Section for the valve control.)
T183-03-07-004

Heavy Lift Solenoid Valve

Heavy Lift
Upon receiving signals from the main controller A, Solenoid Valve
the heavy lift solenoid valve changes the main relief
pressure from the main control valve.
(Refer to the Control System Group in the SYSTEM
Section for the valve control.)

2-Spool EHC Valve Travel Mode

This valve consists of the horsepower increasing Solenoid Valve
solenoid valve ST and oil cooler fan control solenoid
valve SF.
The pressure corresponding to the electric signal
from the main controller A is output to the main T183-03-07-005

pump and regulator of the oil cooler fan motor drive 2-Spool EHC
pump from this valve. Valve
(Refer to the Control System Group in the SYSTEM Horsepower
Section.) Increasing
Solenoid Valve ST
Horsepower Increasing Solenoid Valve ST:
Control of the increasing delivery volume from the Oil Cooler Fan
main pump. Control Solenoid
Valve SF
Oil Cooler Fan Control Solenoid Valve SF:
Control of the oil cooler fan motor rotation speed.
T183-03-07-006

T3-7-7
 COMPONENT OPERATION / Others (Upperstructure)
OIL COOLER FAN MOTOR
The oil cooler fan motor is a inclined-shaft type, fixed
displacement axial plunger motor. The operating
principle of this motor is the same as the travel motor.
(Refer to the Travel Device section in this manual.)

Drive Disk

Rotor

T142-06-04-021

T3-7-8
 COMPONENT OPERATION / Others (Upperstructure)
ACCUMULATOR

The accumulator is provided in the pilot circuit to

buffer fluctuations in oil pressure, and to maintain the
pilot pressure for a short time period after the engine
is stopped.
The accumulator mainly consists of body (5), holder
(4), bladder (2), which encloses nitrogen gas (N2),
and poppet (1). 6
1

• Pressure oil from the pilot pump enters into the

accumulator via port A. Pilot pressure Nitrogen Gas
compresses the nitrogen gas in bladder (2) until 5 (N2)
2
they balance against each other.
4
• When pressure supply is stopped due to engine
stall or any other reasons, bladder (2) starts
expanding, supplying accumulated oil into the Pilot Pressure Oil
pilot circuit via port A. 3

T105-02-10-003C

1 - Poppet 4 - Holder
2 - Bladder 5 - Body
3 - Oil Port 6 - Gas Plug

T3-7-9
 COMPONENT OPERATION / Others (Upperstructure)
AUTO-LUBRICATION SYSTEM

The auto-lubrication system lubricates the front joint Grease Pump

pin automatically. Switch
The main components are grease pump,
auto-lubrication interval switch, auto-lubrication shift
switch and grease pump switch.
This system can be switched AUTO/OFF/MANUAL by
the auto-lubrication shift switch. If the switch is turned
AUTO, the lubrication is performed at the interval set Grease Pump
by the auto-lubrication interval switch. If the switch is
turned OFF, the lubrication is not performed. If the
switch is turned MANUAL, the lubrication must be
performed by using a grease gun (lubrication is not
performed automatically).
T183-03-07-007

T3-7-10
 COMPONENT OPERATION / Others (Undercarriage)
SWING BEARING
This bearing is a single-row shear ball-type bearing, The internal gear of inner race (3) engages with the
comprising outer race (1), inner race (3), balls (6), output shaft of the swing reduction gear.
supports (5), rod and turn buckle (7) and seals (2), (4).
Outer race (1) is bolted to the upperstructure and
inner race (3) is bolted to the undercarriage.

W142-03-01-002

1 - Outer Race 3 - Inner Race 5 - Support 7 - Rod and Turn Buckle

2 - Seal 4 - Seal 6 - Ball

T3-8-1
 COMPONENT OPERATION / Others (Undercarriage)
CENTER JOINT
The center joint is a 360° rotating joint. When the Hydraulic oil flows to the right and left travel motors
upperstructure is rotated, the center joint avoids via the spindle and the oil ports of the body. Seals
twisting of hoses and allows hydraulic oil to flow prevent oil leaks between the spindle and body into
smoothly to or from the travel motors. The spindle is adjacent passages.
attached to the main frame, and the body is bolted to
the swing center of the undercarriage.

Spindle

Body

Seal

W183-03-08-001

T3-8-2
 COMPONENT OPERATION / Others (Undercarriage)
TRACK ADJUSTER
The track adjuster located on the side frame is
composed of spring (5) and adjuster cylinder (6).
Spring (5) absorbs loads applied to the front idler.
Adjuster cylinder (6) adjusts track sag.

• Grease is applied through grease fitting into

chamber A of adjuster cylinder (6) as illustrated
below. The pressure of the grease pushes piston
rod (8) out and decreases track sag.
• To increases track sag, loosen valve (1) 1 to 1.5
turns counterclockwise to release grease from 1
the track adjuster cylinder through the grease Grease Fitting
discharge hole.

CAUTION: The adjusting cylinder is highly

pressurized. Loosening valve (1) quickly
and/or excessively may cause valve (1) to fly
off and the highly pressurized grease to
spout out, possibly resulting in personal
injury. Grease Discharge Hole
Be sure to loosen valve (1) slowly and
gradually, keeping face and body parts away
M104-07-119C
from valve (1). In addition, never attempt to
loosen grease fitting (2).

1 2 3 4 A 5 6 7 8

W142-03-04-016

1 - Valve 3 - Washer 5 - Spring 7 - Flange

2 - Nut 4 - Spacer 6 - Adjuster Cylinder 8 - Piston Rod

T3-8-3
 COMPONENT OPERATION / Others (Undercarriage)
(Blank)

T3-8-4