GROUP 2 MAIN CONTROL VALVE

1. OUTLINE
DOZER BM SW SWING PTO ARM TRAVEL TRAVEL BOOM BUCKET
(Pb1) (Pb2) (Pb3) (Pb4) (Pb5) (Pb6) (Pb7) (Pb8) BOOM (Pb10)
INLET LOCK

T1

B1 B2 B3 B4 B5 B6 P1 B7 B8 B10

A1 A2 A3 P3 A4 A5 A6 P2 A7 A9 A10
T2

(Pa1) (Pa3) (Pa6) (Pa7) (Pa8)

Dr2

(Pa2) ARM IN (Pa4) (Pa5) (Pa10)

(Pb8')

R35Z92MCV01

Port Tightening Port Tightening

Mark Port name Mark Port name
size torque size torque
P1 P1 (A1) pump port 6.0~7.0 A10 Bucket out port PF 4.0~5.0
P2 P2 (A2) pump port PF kgf·m B10 Bucket in port 3/8 kgf·m
T1 Tank return port 1/2 (43.4~50.6 Pa1 Dozer down pilot port
T2 Tank return port lbf·ft) Pb1 Dozer up pilot port
P3 P3 (A3) pump port Pa2 Boom swing (RH) pilot port
A1 Dozer Pb2 Boom swing (LH) pilot port
B1 Dozer Pa3 Swing (RH) pilot port
A2 Boom swing (RH) port Pb3 Swing (LH) pilot port
B2 Boom swing (LH) port Pa5 Arm out pilot port
A3 Swing (LH) port Pb5 Arm in pilot port
B3 Swing (RH) port Pa6 Travel [LH/RR] pilot port 2.5~3.0
4.0~5.0 PF kgf·m
A4 Option port Pb6 Travel [LH/FW] pilot port
PF kgf·m 1/4 (18.1~21.7
B4 Option port Pa7 Travel [RH/RR] pilot port lbf·ft)
3/8 (28.9~36.2
A5 Arm out port lbf·ft) Pb7 Travel [RH/FW] pilot port
B5 Arm in port Pa8 Boom up pilot port
A6 Travel [LH/RR] port Pb8 Boom down pilot port
B6 Travel [LH/FW] port Pa10 Bucket out pilot port
A7 Travel [RH/RR] port Pb10 Bucket in pilot port
B7 Travel [RH/FW] port Dr1, 2 Drain port
A9 Boom up port Pa4 Option pilot port
B8 Boom down port Pb4 Option pilot port

2-9
2. STRUCTURE (1/3)
4-10
4-11 14
4-6
4-5 4-10 4-9
4-12
4-4 4-11
4-8
4-3
4-2
3-6 3-10
3-5 3-8 15
4-7
3-4
4-7 3-3
4-13
4-16 2-6 2-10
4-14 3-7 2-5 2-8
2-4
22
2-3
4-15 1-6
4-17 1-5 1-8
4-18 3-7 15 2-7 1-4
3-2 1-3
1-10
2-7 15 1-7
3-9

3-10 2-2

1-7
2-9
1-2 23
2-10

1-9 24
1-10 R35Z72MCV03

1 Dozer work block 2-9 Cover-pilot 4-6 Plug

1-1 Body-work 2-10 Bolt-soc head w/washer 4-7 O-ring
1-2 Spool assy 3 Swing work block 4-8 Cover-pilot
1-3 Poppet 3-1 Body-work 4-9 Bolt-soc head w/washer
1-4 Spring 3-2 Spool assy 4-10 Plug
1-5 O-ring 3-3 Poppet 4-11 O-ring
1-6 Plug 3-4 Spring 4-12 Plug
1-7 O-ring 3-5 O-ring 4-13 Piston
1-8 Cover-pilot 3-6 Plug 4-14 O-ring
1-9 Cover-pilot 3-7 O-ring 4-15 Body-pilot
1-10 Bolt-soc head w/washer 3-8 Cover-pilot 4-16 Bolt-soc head w/washer
2 Boom swing work block 3-9 Cover-pilot 4-17 Orifice
2-1 Body-work 3-10 Bolt-soc head w/washer 4-18 Filter-coin type
2-2 Spool assy 4 Connecting block 14 Relief valve
2-3 Poppet 4-1 Body-work 15 Overload relief valve
2-4 Spring 4-2 Spool assy 17 O-ring
2-5 O-ring 4-3 Poppet 22 O-ring
2-6 Plug 4-4 Spring 23 Bolt-tie
2-7 O-ring 4-5 O-ring 24 Nut-hex
2-8 Cover-pilot

2-10
 STRUCTURE (2/3)

13

7-8
7-6 15
7-4
13
7-3
6-6 6-10
6-5 6-8
7-5
6-4
6-3
19 15
5-6
6-7 5-5
7-5 15
5-4
18 5-3
7-2
5-10
6-7 15 5-7 5-8
7-7 18
6-2
7-8

6-9 5-7
18
5-2
6-10

5-9
5-10
R35Z92MCV04

5 PTO work block 6-2 Spool assy 7-4 Plug

5-1 Body-work 6-3 Poppet 7-5 O-ring
5-2 Spool assy 6-4 Spring 7-6 Cover-pilot
5-3 Poppet 6-5 O-ring 7-7 Cover-pilot
5-4 Spring 6-6 Plug 7-8 Bolt-soc head w/washer
5-5 O-ring 6-7 O-ring 8 Inlet work block
5-6 Plug 6-8 Cover-pilot 13 Relief valve
5-7 O-ring 6-9 Cover-pilot 15 Overload relief valve
5-8 Cover-pilot 6-10 Bolt-soc head w/washer 17 O-ring
5-9 Cover-pilot 7 Travel work block 18 O-ring
5-10 Bolt-soc head w/washer 7-1 Body work 19 O-ring
6 Arm work block 7-2 Spool assy
6-1 Body-work 7-3 O-ring

2-11
 STRUCTURE (3/3)

117
15
115
119 113
12-10 112
12-6 118 116
12-5 12-8 11-6 114
12-4 12-7 111 112
11-2
12-3 110 120
11-5 107
11-4 102
11-11 101
11-9 104
15 11-12 106 108 109
103
105
10-6 10-10
12-7 11-10
15 10-5 10-8
18 10-4
12-2 10-3
9-6
9-10
9-5 9-8
12-9 11-7 9-4
11-2 11-1 10-7
18 11-8 9-3
11-3
12-10 15

9-7

10-7 18
10-2

9-7
10-9 19
9-2
10-10

9-9

9-10
R35Z72MCV05

9 Travel work block 10-7 O-ring 12-1 Body-work 103 Seal

9-1 Body-work 10-8 Cover-pilot 12-2 Spool assy 104 Filter
9-2 Spool assy 10-9 Cover-pilot 12-3 Poppet 105 Spacer
9-3 Poppet 10-10 Bolt-soc head w/washer 12-4 Spring 106 Ring-retaining
9-4 Spring 11 Boom lock valve 12-5 O-ring 107 Spring A-lock valve
9-5 O-ring 11-1 Body-work 12-6 Plug 108 Spring seat
9-6 Plug 11-2 O-ring 12-7 O-ring 109 Pin
9-7 O-ring 11-3 Plug 12-8 Cover-pilot 110 Poppet
9-8 Cover-pilot 11-4 Poppet 12-9 Cover-pilot 111 Ring-retaining
9-9 Cover-pilot 11-5 Spring 12-10 Bolt-soc head w/washer 112 O-ring
9-10 Bolt-soc head w/washer 11-6 Plug 15 Overload relief valve 113 Guide-piston
10 Boom work block 11-7 O-ring 17 O-ring 114 Piston A1
10-1 Body-work 11-8 Plug 18 O-ring 115 Piston B
10-2 Spool assy 11-9 O-ring 19 O-ring 116 O-ring
10-3 Poppet 11-10 O-ring 20 O-ring 117 Connector
10-4 Spring 11-11 Plug 21 O-ring 118 Ball-steel
10-5 O-ring 11-12 O-ring 101 Cover-lock valve 119 Plug
10-6 Plug 12 Bucket work block 102 Lock valve 120 Bolt-hex. socket head

2-12
3. HYDRAULIC CIRCUIT

Pa1 Pb1
A1
DOZER
B1

Pa2 Pb2
BOOM SWING
A2

B2

Pa3 Pb3
A3 T1
SWING B3
P3

Pp1
Dr1 Boom Up

B4
PTO A4

Pa4 Pb4

B5

ARM
A5
Pa5 Pb5

B6
TRAVEL A6

Pa6 Pb6

P2
Dr1
P1

Pa7 Pb7
A7
TRAVEL B7

Pb8
Pa8

B8 Pb8'
BOOM
A9
Dr2
Pb8' T2

Pa10 Pb10

A10
BUCKET
B10

R35Z92MCV02

2-13
4. FUNCTION

1) IN NEUTRAL (when all spools are in neutral position)

P1 : The oil discharged from the hydraulic pump flows into control valve P1 port, and then flows
through P1 and P2 supply body the P1 side travel spool. The oil flows through the bypass
passage in the direction of travel → boom → bucket spool, and then flows from the bypass
passage to the tank passage in the bucket section.
P2 : The oil discharged for the hydraulic pump flows into the control valve from P2 port, and then
flows through P1 and P2 supply body to the P2 side travel spool. The oil flows through the
bypass passage in the direction of travel → arm → PTO spool, and the flows from the bypass
passage to the tank passage in the PTO section.
P3 : The oil discharged from the hydraulic pump flows into the control valve from P3 port, and then
flows through the parallel passage of dozer, boom swing, and swing. The oil that has followed
into the parallel passage flows through the bypass passage in the direction of dozer → Boom
swing → swing spool, the connecting spool land, the P2 side parallel passage, the bypass
passage from arm to PTO spool, the bypass passage in the PTO section, and then to the tank
passage.
※ Since each line (P1, P2, P3) is supplied with oil from the pump, the section is operatable;
therefore, do not operate the control valve except the working time.
·P1 line : Travel, boom, bucket
·P2 line : Travel, arm, PTO
·P3 line : Dozer, boom swing, arm, PTO, boom (up only)
PP1 : When PP1 port is applied with pilot pressure, the oil flows into the travel independent passage
via an orifice.
With the spool in neutral, the oil flows into Dr1 port provided in the P1 and P2 supply body.

2-14
 P3 side bypass passage

P3 side parallel passage

Pp1

T1
T1

P3

P2 side parallel passage

P2 side bypass passage

P2
P2
Dr1
P1 P1
T2

T2

P1 side parallel
passage

P1 side bypass passage

Tank passage

Hydraulic oil flow in neutral

R35Z72MCV11

2-15
2) TRAVEL OPERATION
For the travel operation, both Pa pressurization and Pb pressurization are the same on operation
so that only Pa pressurization is explained as follows.
When left (right) travel reverse is operated, the secondary pressure from the remote control valve is
applied to Pa6 [Pa7] port to change over the travel spool. The oil flowed from P2 [P1] port flows
through the supply body into the P2 [P1] side bypass passage. The oil flowed into the P2 [P1] side
bypass passage flows through A6 [A7] port that has been opened by the spool changeover to the
travel motor. On the other hand, the oil returned from the travel motor flows into the control valve
from B6 [B7] port and then to the tank passage has been opened after the spool changeover.
The oil flowed from PP1 port flows through the orifice passage provided in the P3 supply section
into the travel independent signal passage.
Although the travel independent passage (see page 2-15) in the travel section that has been
opened during neutral is blocked after the both travel spools changeover, the travel independent
signal passage is connected to the drain port via the bucket section Accordingly, when the bucket
section has not changed over, the connecting spool in the P3 supply section does not change over
because the pressure in the travel independent signal passage is equal to the drain pressure.

Travel motor

A6 B6
(A7) (B7)

Pa6
(Pa7)
Spool changeover
direction
Tank passage

Pilot passage for travel independent signal:

Supply pilot pressure oil via Pp1 port in P3
supply comp.

Pa6
P2
P2
P1
P1

Pa7

Operation during travel(Forward)

R35Z72MCV12

2-16
3) BOOM
OOM OPERATION
Boom up operation
When the boom up operation is carried out, the secondary pressure from the remote control valve
is applied to Pa8 port to change over the boom spool. Since Pa8 port is connected to boom up port
through the piping, the pressure oil supplied to boom up port changes over the connecting spool
through the connecting piston in the P3 supply section
Also, since the P1 side bypass passage is shut off at the boom section after the boom spool
changeover, the oil flowed from P1 port flows through the check valve provided above the bypass
passage in the travel section into the P1 side parallel passage.
On the other side, after the connecting spool changeover the oil flowed into P3 port.
① Flows through the internal passage in connecting spool and the check valve in the P3 supply
section into the P1 side parallel passage.
② The oil flows through the P3 side parallel passage and P3 side bypass passage and then:
a. Flows through the check valve in the P3 supply section into the P1 side parallel passage.
b. Some oil flows through the orifice passage provided in the connecting spool and the check
valve in the P3 supply section into the P2 side parallel passage.
The oil flowed into the P1 side parallel passage is connected with the oil from P1 pump.
The oil flowed into the P2 side parallel passage flows through the bypass passages in the arm
section and PTO section to the tank passage.
Since the passage connected to the boom lock valve and the bridge passage are opened after the
boom spool changeover, the oil flowed into the P1 side parallel passage flows through the load
check valve in the boom section and the bridge passage into the boom lock valve section
The oil flowed into the boom lock valve section opens the lock valve (free flow condition), flows into
A9 port, and the to the head side of the boom cylinder.
On the other hand, the oil returned from the rod side of the boom cylinder flows into B8 port to the
tank passage that has opened with the spool's notch after the spool changeover. Then, the boom
cylinder extends to raise the boom.

2-17
P1 side circuit

Bridge passage
B8
Oil flows into lock valve comp. and
then out of A9 port through lock valve

Pa8
Spool changeover
direction
parallel passage

P1
T1 Dr1 P1

Boom

Boom lock
valve comp
T2
To bridge passage
in boom comp. To cylinder head side To B8 port
via A9 port via cylinder rod side

P3 side (Connecting side) circuit

To P2 side parallel passage To P1 side parallel passage
P3
Connecting piston

Pa8

Boom up

From P3 side bypass passage From P3 side bypass passage

To P3 side parallel passage
P3 From P3 side bypass passage

P3

To P2 side parallel passage To P1 side parallel passage

Oil flows into P2 side parallel passage and then
out of PTO bypass passage to tank passage

Boom up operation
R35Z72MCV13

2-18
 Boom down operation
When the boom down operation is carried out, the secondary pressure from the remote control
valve is applied to Pb8 port to change over the boom spool.
Since Pb8 port is connected to Pb8' port through the piping, the pressure is also applied to pb8'
port (boom lock valve release port) to release the boom lock valve.
(for the explanation of boom lock valve operation, see pages 2-20, 21)
Since the bypass passage is shut off at the boom section after the spool changeover (some oil
flows through the orifice passage provided in the boom spool's bypass passage to the downstream
side of the bypass passage), the oil flowed from P1 port flows through the check valve provided
above the bypass passage in the travel section into the P1 side parallel passage.
Also, since a passage between B8 port and bridge passage is opened with the spool's notch after
the spool changeover, the oil flowed into the P1 side parallel passage flows through the load check
valve in the boom section into B8 port via the bridge passage and then into the rod side of the
boom cylinder.
On the other side, the oil returned from the head side of the boom cylinder flows into A9 port to the
tank passage that has been opened with the spool's notch after the spool changeover through the
boom lock valve that has been released by Pb8' port pressure. Then, the boom cylinder retracts to
lower the boom.

Oil flows from A9 port into

T2 B8
boom comp. via lock valve

Pb8

Spool changeover
direction
Some oil flows to downstream side

P1
T1 Dr1 P1

Boom

Boom lock
valve comp
T2
To bridge passage To A9 port via To cylinder rod side
in boom comp. cylinder head side via B8 port
Pb8'
Lock valve Some oil flows to downstream side
release signal

Boom down operation

R35Z72MCV14

2-19
4) Operation of boom lock valve
(1) Holding
In the boom spool neutral condition,
·The pilot piston chamber (a) is connected to the drain passage through the pilot port (Pb8') for
releasing the boom lock valve.
·The piston chamber (b) is also connected to the drain passage through the drain port (Dr2).
Therefore, the piston (B) maintains the condition shown in the figure.
The boom cylinder holding pressure (shown in half-tone dot meshing) is applied to the lock valve
chamber as shown in the figure to :
·Press the needle valve against the needle valve seat.
·Press the lock valve against the body seat.
Then, oil leakage from the boom cylinder head side is prevented to stop the movement of the
boom cylinder due to leakage.

B8 port
Piston chamber(b) Holding pressure

Body seat
Neddle valve seat

Lock valve
chamber
Pilot piston A9
chamber(a)
Dr2

Pb8'

Piston B Piston A Lock valve

Needle
valve
Force applied to neddle valve
Force applied to lock valve

Operation of boom lock valve (holding)

R35Z72MCV15

2-20
(2) Release
When the pilot pressure is applied to the pilot port (Pb8') for boom lock valve release, the piston
(B) moves rightward to open the needle valve through the piston (A1).
Then, the oil returned from the boom cylinder flows through the passage in the direction of lock
valve's orifice → lock valve chamber → needle valve seat → check valve into the lock valve's
downstream side chamber (boom section).
When the lock valve's downstream chamber is connected to the tank passage after the boom
spool changeover and the needle valve is released, the pressure in the lock valve chamber
decreases to open the lock valve by the oil returned from the boom cylinder. The returned oil flows
into the tank passage with the boom spool's notch to operate the cylinder.

B8 port
Piston chamber(b)

Check valve Body seat

Lock valve
chamber
Pilot piston A9
chamber(a)
Dr2

Pb8'

Piston B Piston A1 Needle

valve Lock valve Orifice
Needle valve seat

Operation of boom lock valve (release)

R35Z72MCV16

2-21
5) BUCKET
UCKET OPERATION
Bucket
ucket in operation
When the bucket in operation is carried out, the secondary pressure from the remote control valve
flows into Pb10 port to change over the bucket spool.
Since the P1 side bypass passage is shut off at the bucket section after the bucket spool
changeover, the oil flowed from P1 port flows through the check valve provided above the bypass
passage in the travel section into the P1 side parallel passage.
Also, since a passage between B10 port and the bridge passage is opened after the spool
changeover, the oil flowed into the P1 side parallel passage flows through the load check valve in
the bucket section into B10 port via the bridge passage and then the head side of the bucket
cylinder.
On the other hand, the oil returned from the rod side of the bucket cylinder flows into A10 port to
the tank passage that has opened with the spool's notch after the spool changeover. Then, the
bucket cylinder extends to make the bucket in.

A10 B10

Pb10

Spool changeover
direction
P1 side parallel passage

T1 P1 Dr1 P1

Boom

Boom lock
valve comp
T2

Bucket

To bridge passage To A10 port via To cylinder head side

in bucket comp. cylinder rod side via B10 port

Bucket in operation

R35Z72MCV17

2-22
Bucket
ucket out operation
When the bucket out operation is carried out, the secondary pressure from the remote control valve
flows into Pa10 port to change over the bucket spool.
Since the P1 side bypass passage is shut off at the bucket section after the bucket spool
changeover, the oil flowed from P1 port flows through the check valve provided above the bypass
passage in the travel section into the P1 side parallel passage.
Also, since a passage between A10 port and the bridge passage is opened after the spool
changeover, the oil flowed into the P1 side parallel passage flows through the load check valve in
the bucket section into A10 port via the bridge passage and then the head side of the bucket
cylinder.
On the other hand, the oil returned from the head side of the bucket cylinder flows into B10 port to
the tank passage that has opened after the spool changeover.

A10 B10

Pa10

Spool changeover
direction
P1 side parallel passage

T1 P1 Dr1 P1

Boom

Boom lock
valve comp
T2

Bucket

To bridge passage To cylinder rod side To B10 port via

in bucket comp. via A10 port cylinder head side

Bucket out operation

R35Z72MCV18

2-23
6) ARM
RM OPERATION
Arm
rm in operation
When the arm in operation is carried out, the secondary pressure from the remote control valve is
applied to Pb5 port to change over the arm spool. The secondary pressure is also applied to the
pilot chamber (arm in port) on the connecting section spring chamber side that has been
connected through the piping. Therefore, when the operation is carried out together with the boom
up operation at the same time, the connecting spool is hard to change over against the pilot
pressure for arm in operation.
Since the P2 port bypass passage is shut off at the arm section after the arm spool change over,
the oil flowed from P2 port flows through the travel section and a passage between travel section
and arm section into the P2 side parallel passage.
Also, since the oil flowed from P3 port flows through the direction of dozer → boom swing → swing
section and then into the P2 side parallel passage via the check valve in the P3 supply section, the
connecting flow of P2 pump and P3 pump is supplied to the P2 side parallel passage. [Although
the P3 side bypass passage is also connected to the P1 side parallel passage through the check
valve in the P3 section, there is no oil flow into the P1 side as long as the P1 side sections (boom ,
bucket) are not operated.]
Since a passage between B5 port and the bridge passage is opened after the spool changeover,
the oil flowed into the P2 side parallel passage flows through the load check valve in the arm
section into B5 port via the bridge passage and then into the head side of the arm cylinder.
On the other hand, the oil returned from the rod side of the arm cylinder flows into A5 port to the
tank passage that has opened with the spool's notch after the spool changeover. Then, the arm
cylinder extends to make the arm in.

A5 B5

Pb5

Spool changeover
direction

P3
P3

Arm in To cylinder head side

via B5 port
Pb5

T1 To bridge passage

PTO
Arm

Travel
To A5 port via
cylinder rod side

P2

P2
T2

Arm in operation R35Z72MCV19

2-24
Arm out operation
When the arm out operation is carried out, the secondary pressure from the remote control valve is
applied to Pa5 port to change over the arm spool.
Since the P2 side bypass passage is shut off at the arm section after the arm spool changeover,
the oil flowed from P2 port flows through the travel section and a passage between travel section
and arm section into the P2 side parallel passage.
Also, since the oil flowed from P3 port flows through the direction of dozer → boom swing → swing
section and then into the P2 side parallel passage via the check valve in the P3 supply section, the
connecting flow of P2 pump and P3 pump is supplied to the P2 side parallel passage. [Although
the P3 side bypass passage is also connected to the P1 side parallel passage through the check
valve in the P3 section, there is no oil flow into the P1 side as long as the P1 side sections (boom ,
bucket) are not operated.]
Since a passage between A5 port and the bridge passage is opened after the spool changeover,
the oil flowed into the P2 side parallel passage flows through the load check valve in the arm
section into A5 port via the bridge passage and then into the rod side of the arm cylinder.
On the other hand, the oil returned from the head side of the arm cylinder flows into B5 port to the
tank passage that has opened after the spool changeover. Then, the arm cylinder retracts to make
the arm out.

A5 B5

Pa5
Spool changeover
direction

P3
P3

To cylinder rod
side via A5 port
T1 To bridge
passage
PTO
Arm

Travel

P2 To B5 port via
cylinder head side

P2
T2

Arm out operation

R35Z72MCV20

2-25
7) PTO OPERATION
For the PTO operation, both Pa pressurization and Pb pressurization are the same on operation so
that only Pa pressurization is explained as follows.
When the PTO operation (Pa4 pressurization) is carried out, the secondary pressure from the
remote control valve is applied to Pa4 port to change over the PTO spool. Since the P2 side bypass
passage is shut off at the PTO section after the PTO spool changeover, the oil flowed from P2 port
flows through the travel section and a passage between travel section and arm section into the P2
side parallel passage.
Also, since the oil flowed from P3 port flows through the direction of dozer → boom swing → swing
section and then into the P2 side parallel passage via the check valve in the P3 supply section, the
connecting flow of P2 pump and P3 pump is supplied to the P2 parallel passage.
[Although the P3 side bypass passage is also connected to the P1 side parallel passage through
the check valve in the P3 section, there is no oil flow into the P1 side as long as the P1 side
sections (boom , bucket) are not operated.]
Since a passage between A4 port and the bridge passage is opened after the spool changeover,
the oil flowed into the P2 side parallel passage flows through the load check valve in the PTO
section into A4 port via the bridge passage and then into the actuator for PTO.
On the other hand, the oil returned from actuator for PTO flows into B4 port to the tank passage
that has opened after the spool changeover.

A4 B4

Pa4
Spool changeover
direction

P3
P3
To bridge passage
in PTO comp.

To actuator
T1 via A4 port
PTO

Arm

Travel

To B4 port via
P2 actuator

P2
T2

PTO operation R35Z72MCV21

2-26
 8) DOZER
OZER OPERATION
Dozer
ozer up operation
When the dozer up operation is carried out, the secondary pressure from the remote control valve
is applied to Pa1 port to change over the dozer spool.
Since the P3 side bypass passage is shut off at the dozer section after the dozer spool
changeover, the oil flowed from P3 port through the P3 side parallel passage flows into A1 port
through the load check valve in the dozer section and the bridge passage since A1 port and the
bridge passage have been opened after the spool changeover and then into the rod side of the
dozer cylinder.
On the other hand, the oil returned from the head side of the dozer cylinder flows into B1 port to the
tank passage that has opened after the spool changeover.
Then, the dozer cylinder retracts to raise the dozer.

A1 B1

Pa1

Spool changeover
direction

To cylinder rod To B1 port via

Cylinder head side
To bridge passage side via A1 port
in dozer comp.

Dozer

Boom swing

Swing

P3
P3

Supply
(connecting)
T1

Dozer up operation

R35Z72MCV22

2-27
 Dozer
ozer down operation
When the dozer down operation is carried out, the secondary pressure from the remote control
valve is applied to Pb1 port to change over the dozer spool.
Since the P3 side bypass passage is shut off at the dozer section after the dozer spool
changeover, the oil flowed from P3 port through the P3 side parallel passage flows into B1 port
through the load check valve in the dozer section and the bridge passage since B1 port and the
bridge passage have been opened after the spool changeover and then into the head side of the
dozer cylinder.
On the other hand, the oil returned from the rod side of the dozer cylinder flows into A1 port to the
tank passage that has opened with the spool's notch after the spool changeover.
Then, the dozer cylinder extends to lower the dozer.

A1 B1

Pb1

Spool changeover
direction

To A1 port via
To bridge passage To cylinder head
Cylinder rod side
in dozer comp. side via B1 port

Dozer

Boom swing

Swing

P3
P3
Supply
(connecting)
T1

Dozer down operation

R35Z72MCV23

2-28
 9) BOOM
OOM SWING OPERATION
Boom
oom left swing operation
When the boom left swing operation is carried out, the secondary pressure from the remote control
valve is applied to Pb2 port to change over the boom swing spool.
Since the P3 side bypass passage is shut off at the boom swing section after the boom swing
spool changeover, the oil flowed from P3 port through the P3 side parallel passage flows into B2
port through the load check valve in the boom swing section and the bridge passage since B2 port
and the bridge passage have been opened after the spool changeover and then into the rod side of
the boom swing cylinder.
On the other hand, the oil returned from the head side of the boom swing cylinder flows into A2
port to the tank passage that has opened with the spool's notch after the spool changeover.
Then, the boom swing cylinder retracts to swing the attachment left.

A2 B2

Pb2

Spool changeover
direction

To A2 port via To cylinder rod

Cylinder head side side via B2 port
To bridge passage
in boom swing comp.
Dozer

Boom swing

Swing

P3 P3

Supply
(connecting)

T1

Boom left swing operation

R35Z72MCV24

2-29
Boom
oom right swing operation
When the boom right swing operation is carried out, the secondary pressure from the remote
control valve is applied to Pa2 port to change over the boom swing spool.
Since the P3 side bypass passage is shut off at the boom swing section after the boom swing
spool changeover, the oil flowed from P3 port through the P3 side parallel passage flows into A2
port through the load check valve in the boom swing section and the bridge passage since A2 port
and the bridge passage have been opened after the spool changeover and then into the head side
of the boom swing cylinder.
On the other hand, the oil returned from the rod side of the boom swing cylinder flows into B2 port
to the tank passage that has opened with the spool's notch after the spool changeover.
Then, the boom swing cylinder extends to swing the attachment right.

A2 B2

Pa2
Spool changeover
direction

To cylinder head To B2 port via

side via A2 port Cylinder rod side
To bridge passage
in boom swing comp.
Dozer

Boom swing

Swing

P3 P3

Supply
(connecting)
T1

Boom right swing operation

R35Z72MCV25

2-30
(10) SWING OPERATION
For the swing operation, both Pa pressurization and Pb pressurization are the same on operation
so that only Pa pressurization is explained as follows.
When the right swing operation is carried out, the secondary pressure from the remote control
valve is applied to Pa3 port to change over the swing spool.
Since the P3 side bypass passage is shut off at the swing section after the swing spool
changeover, the oil flowed from P3 port through the P3 side parallel passage flows into A3 port
through the load check valve in the swing section and the bridge passage since A3 port and the
bridge passage have been opened after the spool changeover and then into the swing motor.
On the other hand, the oil returned from the swing motor flows into B3 port to the tank passage that
has opened with the spool's notch after the spool changeover.
Then, the upper swing body swings right.

A3 B3

Pa3

Spool changeover
direction

To swing motor To B3 port via

via A3 port swing motor

Dozer
To bridge passage
in swing comp.
Boom swing

Swing
P3
P3

Supply
(connecting)

T1

Right swing operation

R35Z72MCV26

2-31
(11) COMBINED CONTROL OPERATION ①
Boom up + Arm in + bucket
When the above combined control is carried out, the secondary pressure from the remote control
valve is applied to each spool to change over them. Since the secondary pressure for arm in
operation is also applied to the pilot chamber on the connecting section spring chamber side
according to the piping, the connecting spool operates against the secondary pressure developed
from boom up operation and arm in operation.
(boom up operation secondary pressure - Arm in operation secondary pressure =
connecting spool changeover pressure)
When all the above combined operations are carried out in full lever operation (full changeover), the
oil supplied from P1 pump is supplied to the boom and bucket and the oil from P2 pump to the arm.
Since the connecting spool changeover pressure becomes "0" as mentioned above, the
connecting spool cannot change over and the oil from P3 pump flows to the P1 and P2 side
parallel passages through the connecting section. Accordingly, much oil flows to the arm side
normally because of its low working load.
In this condition, since gradually restricting the arm in operation (returning the lever) causes the
secondary pressure for arm in operation to decrease, the connecting spool changeover pressure to
increase, the connecting spool to start changing over, and the passage to the arm side to be
narrowed, the oil supplied from P3 pump flows abundantly into the P1 side (boom, bucket).
As mentioned above, the oil supplied from P3 pump flows suitably into each attachment according
to the control input during the above combined control, resulting in a well-balanced and efficient
working speed.
Besides, since the oil flow to the bucket whose working load is less than the boom is restricted with
an orifice (the orifice of boom priority) provided before the bucket section in the P1 side parallel
passage, much oil flows into the boom section. As a result, the working speed balance between
both attachments is maintained during the combined operation of boom and bucket.

2-32
P3 side (connecting side) circuit
To P2 side parallel passage
To P1 side parallel passage
P3
T1

Arm in Boom up

From P3 side bypass passage

To P3 side parallel passage

From P3 side bypass passage
P3

To P2 side parallel passage Oil flows into P2 side parallel passage and To P1 side parallel passage
out of the tank passage through the bypass
passage in PTO comp.

P1 side circuit (the orifice of boom priority)

P1
T1
P1

From P3
connecting
comp. To bridge passage
in boom comp.

T2

The orifice of boom priority

To cylinder rod side via A10 port To B10 port
through bridge passage in bucket comp. via cylinder head side

Oil flow during combined operation

R35Z72MCV27

2-33
(12) COMBINED CONTROL OPERATION ②
Both travels + bucket
When the both travels operation is carried out together with the bucket operation at the same time,
the oil flowed from Pp1 port flows through the orifice passage and into the travel independent
signal passage; both travels and the bucket spool changeover make a passage to the drain port
shut off.
Then, the travel independent passage becomes the same pressure as Pp1 port pressure (pilot
primary pressure).
When the travel independent passage becomes Pp1 pressure, the Pp1 pressure is applied to the
connecting spool to change over the connecting spool.
Since the bypass passage from P3 to P2 side, which is a passage to the tank, in restricted, the oil
from P3 side flows into the P1 side parallel passage that is connected through a check valve.
With his circuit arrangement, the bucket section is supplied with pressure oil from P3 during both
travels operation, the simultaneous operation becomes possible.
Besides, since each of P1 and P2 is used independently during both travels and only P3 is used for
bucket operation, stable travel is possible to continue even if there is change in the bucket load.

To P1 side parallel passage

P3
To P1 side parallel passage

T1

P3 Pp1

To travel motor

P2 P2

Dr1 P1
P1

To travel motor

Boom lock
valve comp.
T2
Bucket

Oil flows from P1 side parallel passage, through the bridge passage
in the bucket comp., and in to the cylinder rod side via A10 port.

Travel independence operation

R35Z72MCV28

2-34
(13) MAIN AND PORT RELIEF VALVE OPERATION
Main relief valve operation
Main relief valves (MRV) are different in the uses for P1/P2 and P3; however, their structures and
operation are the same.
① Pressure oil flows through the inside of the piston built in the pressure regulating valve (poppet-
main V') and the orifice B and then into the internal chamber A until it is filled up. The filled up
pressure causes both of the pressure regulating valve and the socket and body seat to be seated
securely.
Regulating valve spring
Socket Orifice B Piston (Spring-pilot)
Tank passage

Body seat
Pressure regulating Chamber A Regulating valve
(Poppet-main V') (poppet-pilot)

MRV operation (1) R35Z72MCV29

② When the oil pressure at port P increases up to the setting pressure of regulating valve spring,
the pressure oil is applied to the regulating valve via the piston to open the regulating valve. Then,
the pressure oil flows through a passage in the direction of piston inside → orifice B → chamber
A → circular orifice C → Drill hole D and the external of socket and then into the tank passage.

Circular orifice C Drill hole D

MRV operation (2) R35Z72MCV30

③ Since the pressure inside the chamber A decreases when the regulating valve is opened, which
causes the pressure regulating valve to open to let the pressure oil port P flows into the tank
passage through drill hole E.

Drill hole E

R35Z72MCV31
MRV operation (3)

④ Also, since the regulating valve is pressed to the seat by regulating valve spring when the
pressure at port P decreases below the setting pressure of regulating valve spring, the pressure
inside chamber A becomes the same as the pressure at port P to cause the pressure regulating
valve to be pressed to the seat, resulting in the original condition (①).

2-35
Overload relief valve (ORV) operation ①
① Pressure oil flows through the inside of the piston built in the pressure regulating valve (poppet-
main V') and the orifice B and then into the internal chamber A until it is filled up. The filled up
pressure causes both of the pressure regulating valve and socket and body seat to be seated
securely.
Regulating valve spring
Socket Orifice B Piston (Spring-pilot)
Tank passage

Body seat
Pressure regulating Chamber A Regulating valve
(Poppet-main V') (poppet-pilot)

ORV operation (1) R35Z72MCV32

② When the oil pressure at port P increases up to the setting pressure of regulating valve spring,
the pressure oil is applied to the regulating valve via the piston to open the regulating valve. Then,
the pressure oil flows through a passage in the direction of piston inside → orifice B → chamber
A → circular orifice C → Drill hole D and the external of socket and then into the tank passage.

Circular orifice C Drill hole D

ORV operation (2) R35Z72MCV33

③ Since the pressure inside the chamber A decreases when the regulating valve is opened, which
causes the pressure regulating valve to open to let the pressure oil port P flows into the tank
passage through drill hole E.

Drill hole E

ORV operation (3) R35Z72MCV34

④ Also, since the regulating valve is pressed to the seat by regulating valve spring when the
pressure at port P decreases below the setting pressure of regulating valve spring, the pressure
inside chamber A becomes the same as the pressure at port P to cause the pressure regulating
valve to be pressed to the seat, resulting in the original condition (①).

2-36
Overload relief valve (ORV) operation ②【 ②【operation
operation during suction】
suction
If there is negative pressure at port P (or the tank passage pressure is higher than P pressure),
the socket is applied with press and open force. Then, the opening between body seat and
socket increases to cause the oil to flow into port P from the tank passage, filling up the space.

Tank passage

Body seat Socket

ORV operation (during suction) R35Z72MCV35

2-37