SECTION 6 HYDRAULIC SYSTEM
Group 1 Structure and function -------------------------------------------------------------------------------------- 6-1
Group 2 Operational checks and troubleshooting -------------------------------------------------------- 6-17
Group 3 Disassembly and assembly ----------------------------------------------------------------------------- 6-21
SECTION 6 HYDRAULIC SYSTEM
GROUP 1 STRUCTURE AND FUNCTION
1. HYDRAULIC CIRCUIT (LEVEL TYPE)
6 7
8 9 3
2
LIFT TILT AUX 1 AUX 2
10 11
12
35B7HS01
1 Hydraulic gear pump 7 Tilt cylinder
2 Priority valve 8 Down safety valve
3 Main control valve 9 Down flow regulator
4 Steering unit 10 Suction strainer
5 Steering cylinder 11 Return filter
6 Lift cylinder 12 Hydraulic oil tank
6-1
HYDRAULIC CIRCUIT (FINGERTIP TYPE)
6 7
8 9 LIFT SC LC A B A B
5 3
M2
L R
4
M1
12.0MPa
T LS P
P T
MOTOR 1
10 11
12
40B96HS01A
1 Hydraulic gear pump 7 Tilt cylinder
2 Priority valve 8 Down safety valve
3 Main control valve 9 Down flow regulator
4 Steering unit 10 Suction strainer
5 Steering cylinder 11 Return filter
6 Lift cylinder 12 Hydraulic oil tank
6-2
1) WHEN THE LIFT CONTROL LEVER IS IN THE LIFT POSITION
6 7
8 3
9
2
LIFT 2
Return line
Steering
system
10 11
12
35B7HS02
When the lift control lever is pulled back, the spool on the first block is moves to lift position.
The oil from hydraulic gear pump (1) flows into main control valve (3) and then goes to the large
chamber of lift cylinder (6).
The oil from the small chamber of lift cylinder (6) returns to hydraulic oil tank (12) at the same time.
When this happens, the forks go up.
6-3
2) WHEN THE LIFT CONTROL LEVER IS IN THE LOWER POSITION
6 7
8 9 3
2
Return line
LOWER
Steering
system
10 11
12
35B7HS03
When the lift control lever is pushed forward, the spool on the first block is moved to lower position.
The work port(1A) and the small chamber and the large chamber are connected to the return
passage, so the forks will be lowered due to its own weight.
6-4
3) WHEN THE TILT CONTROL LEVER IS IN THE FORWARD POSITION
6 7
8 9 3
Return line
TILT
Steering FORWARD
system
LIFT AUX 1 AUX 2
10 11
12
35B7HS04
When the tilt control lever is pushed forward, the spool on the second block is moved to tilt forward
position.
The oil from hydraulic gear pump (1) flows into main control valve (3) and then goes to the large
chamber of tilt cylinder (7) by pushing the load check valve of the spool.
The oil at the small chamber of tilt cylinder (7) returns to hydraulic tank (12) at the same time.
When this happens, the mast tilt forward.
6-5
4) WHEN THE TILT CONTROL LEVER IS IN THE BACKWARD POSITION
6 7
8 9 1A 2B 2A 3B 3A 4B 4A 3
2
150kgf/cm
2
210kgf/cm
Return line
Steering
system
T LIFT P TILT AUX 1 AUX 2 G
BACKWARD
LS CF EF
2
MOTOR 1
10 11
12
35B7HS05
When the tilt control lever is pulled back, the spool on the second block is moved to tilt backward
position.
The oil from hydraulic gear pump (1) flows into main control valve (3) and then goes to the small
chamber of tilt cylinder (7) by pushing the load check valve of spool.
The oil at the large chamber of tilt cylinder (7) returns to hydraulic tank (12) at the same time.
When this happens, the mast tilt backward.
6-6
2. HYDRAULIC GEAR PUMP
1) STRUCTURE
1 19 18 11 10 17 14 6 15 16
8 9 7 2 3 4 5 13 12
35B7HS06
1 Flange 8 Screw 14 Plate
2 Body 9 Nut 15 Seal
3 Drive gear 10 Lip seal 16 Seal
4 Driven gear 11 Circlip 17 Seal
5 Floating gear 12 Bushing 18 Name plate
6 Key 13 Center plate 19 Screw
7 Washer
6-7
3. MAIN CONTROL VALVE
1) STRUCTURE (4- Spool)
3 2
G F F
4
I
1
6
Gauge port Inlet port
4B 3B 2B Outlet port
E
4A 3A 2A
27 25
I
5 7
E G F F
26 12
SECTION H - H 13
16 15 14
18 28 9
17 8 10
30
29
SECTION T - T 31
SECTION E - E 11
32
15
19 22 H 24 15
23 22
T T 19 23
20 21 8 9
VIEW I - I VIEW G - G VIEW F - F
Port name Size Port name Size
2A, 2B, 3A, 3B, 4A, 4B 3/4-16UNF-2B Inlet port 1-1/16-12UNF-2B
Gauge port PF1/4 Outlet port 1-1/16-12UNF-2B
35B7HS07
1 Lift block assy 12 Relief piston 22 O-ring
2 Tilt block assy 13 Nut 23 O-ring, retainer
3 Aux1 block assy 14 Relief plug 24 Plug
4 Aux2 block assy 15 O-ring 25 Steel ball
5 T cover 16 Relief spring 26 Load sensor spring
6 Gauge plug assy 17 Pilot poppet 27 Load sensor spring
7 Long bolt 18 Plug 28 O-ring
8 Hydrostat plug 19 O-ring 29 System relief seat
9 O-ring 20 O-ring 30 Secondary relief seat
10 Hydrostat spring 21 O-ring 32 Solenoid valve assy
11 Hydrostat sleeve
6-8
2) INLET SECTION OPERATION
(1) Structure and description
(Relief valve piston) 12 13
14
16
28 8 9 10
17
30
Relief valve piston
29
11
20D7HS08
8 Hydrostat plug 14 Relief plug
9 O-ring 16 Relief spring
10 Hydrostat spring 17 Pilot poppet
11 Hydrostat sleeve 28 O-ring
12 Relief piston 29 System relief seat
13 Nut 30 Secondary relief seat
6-9
(2) Operation
Secondary relief valve
To neutral passage
P
15.0MPa To aux block
System relief valve
T 21.0MPa
P To neutral passage
1
To load check valve
35B7HS15
Oil flows from P (pump) port to reservoir (T) by pushing hydrostat spool (1).
Before the center bypass line closed, hydrostat spool is keep opening, so pump port (P) and tank
port (T) are always connected in operation to minimize heat generation.
6-10
3) LIFT SECTION OPERATION
(1) Lift position
1A
Load check valve
35B7HS09
When the lift control lever is pulled back, the spool moves to the right and the neutral passage is
closed.
The oil supplied from the pump pushes up the load check valve and flow into lift cylinder port (1A).
The pump pressure reaches proportionally the load of cylinder and fine control finished by shut off
of the neutral passage.
The return oil from cylinder flows into the tank.
6-11
(2) Lower position
1A
35B7HS10
When the lift control lever is pushed forward, the spool moves to the left and the neutral passage is
closed.
The spool moves to the lift lower position, opening up the neutral passage to tank and (1A) → T.
In lift lower position the fork drops due to its own weight.
6-12
4) TILT SECTION OPERATION
(1) Tilt forward position
2B 2A
Tilt lock spool
Load check valve 35B7HS11
When the tilt control lever is pushed forward, the spool moves to the left and the neutral passage is
closed.
The oil supplied from the pump pushes up the load check valve and flow into tilt cylinder port (2B).
The pump pressure reaches proportionally the load of cylinders and fine control finished by closing
the neutral passage.
The return oil from cylinder port (2A) flows into the tank through the hole of the tilt lock spool.
6-13
(2) Tilt backward position
2B 2A
Tilt lock spool
Load check valve
35B7HS12
When the tilt control lever is pulled back, the spool moves to the right and the neutral passage is
closed.
The oil supplied from the pump pushes up the load check valve and flows into tilt cylinder port (2A).
The pump pressure reaches proportionally the load of cylinder and fine control finished by shut off
of the neutral passage.
The return oil from cylinder port (2B) flows into the tank via the low pressure passage.
6-14
5) MAIN RELIEF VALVE
(1) Pressure setting
Lock nut Relief plug Seat
A good pressure gauge must be installed
in the line which is in communication with
the work port relief. A load must be
applied in a manner to reach the set
Adjust bar
pressure of the relief unit.
Relief spring
Procedure O-ring
① Loosen lock nut. Pilot poppet
② Set adjusting bar to desired pressure
T
setting.
③ Tighten lock nut. Main relief valve : 210 bar
④ Retest in similar manner as above.
P
35B7HS20
(2) Operation
Pressurized oil over the relief pressure
pushes pilot poppet and flows to tank Pilot poppet
passage, therefore the system pressure
keeps under the adjusted relief pressure.
HP
Relief spring
T
35B7HS21
6-15
4. LIFT CYLINDER
9 10 8 11 13 12 1 2 14 15 3 7 6 4,5
D255HS18
1 Tube assembly 6 Wear ring 11 O-ring
2 Rod 7 Retaining ring 12 Guide
3 Piston 8 Gland 13 DU bushing
4 Piston seal 9 Dust wiper 14 Spacer
5 Back up ring 10 Rod seal 15 O-ring
5. TILT CYLINDER
24 18 19,20 21,22,23 8,7 3 12 11 5,6 9,10 4 1 2 14 15 16 13 17
25 25
35B7HS25
1 Tube assembly 10 Back up ring 18 Rod eye
2 Rod 11 Lock washer 19 Spherical bearing
3 Gland 12 Washer 20 Retaining ring
4 Du bushing 13 Piston 21 Hexagon bolt
5 Rod seal 14 O-ring 22 Hexagon nut
6 Back up ring 15 Back up ring 23 Spring washer
7 Dust wiper 16 Wear ring 24 Grease nipple
8 Snap ring 17 Nylon nut 25 O-ring
9 O-ring
6-16
