INTRODUCTION

GENERAL

This section has the description and operation of the hy-
draulic system. The section also has repair procedures
and troubleshooting for most of the components of the
hydraulic system. See the sections STEERING SYS-
TEM, 1600 SRM 671 and THE BRAKE SYSTEM,
1800 SRM 659 for information on these systems. The
section HYDRAULIC GEAR PUMPS, 1900 SRM 97
has the repair procedures for hydraulic pumps.

SYSTEM DESCRIPTION AND OPERATION
(See FIGURE 2. and FIGURE 1.)

The hydraulic system includes the circuits for the mast,
steering system, brake system, carriage and attach-
ments. A three–section gear pump supplies the flow of
oil for the components of the hydraulic system. The
pump is driven by a power take–off arrangement on the
transmission housing. The inlet hose for each pump sec-
tion is connected to the hydraulic tank.

The hydraulic system uses a three–section hydraulic
pump. The three sections of the pump supply different
parts of the hydraulic system. The smallest section of the
pump supplies oil to the pilot supply valve. The middle
section of the pump supplies oil to the main control
valve for the lift, tilt and auxiliary circuits. The large
section of the pump supplies oil to a priority valve in the
main control valve. The operation of the priority valve is
controlled by pilot pressure in the load sensing circuit of
the steering control unit. Oil that is not needed for steer-
ing flows to the lift circuit.

Most of the valves in the hydraulic system are installed
on a module. The module is installed on rubber isolators
in a compartment in the left side of the frame.

Main Control Valve

The main control valve controls the steering priority
flow and the lift, lower, tilt and auxiliary functions. The
control valve has five spools; one for steering priority,
two for the lift circuit and one each for the tilt and auxil-
iary functions.

Remote Control Valve

The remote control valve is controlled by the operator.
The valve has two sections. One section controls the lift-
ing and lowering function and the other section controls
the tilt function. Pilot lines for hydraulic oil are con-
nected between the remote control valve and the main
control valve. Movement of the spools in the remote
control valve actuates the spools for the lift and tilt cir-
cuits. The supply of oil for the remote control valve
comes from the pilot supply valve.

Pilot Supply Valve

The pilot supply valve controls the flow of oil to the cir-
cuits for the following: remote control valve, auxiliary
control valve, brake system and the accumulator.

Auxiliary Control Valve

The auxiliary control valve is a solenoid operated valve
that controls the auxiliary spool in the main control
valve. The operator actuates the auxiliary control valve
with switches in the operator’s compartment. The auxil-
iary spool starts and stops the flow of oil to the selector
valves on the carriage for the separate hydraulic func-
tions. The auxiliary control valve receives oil pilot sup-
ply valve.

Selector Valves

The selector valves are solenoid valves that are as-
sembled together and installed on the carriage or attach-
ment. The supply and return ports in the manifold for the
selector valves are connected to the control valve for the
carriage and attachment with hoses on the mast. Each
selector valve opens or closes a hydraulic circuit to a
cylinder or cylinders for a specific function. Each selec-
tor valve is actuated by a switch that also actuates the
auxiliary control valve at the same time.

Steering System

The oil supply for the steering system comes from the
priority valve in the main control valve. The movement
of the priority spool is controlled by a pilot line (load
sensing) from the steering control unit. Oil that is not
used for steering flows to the lift circuit in the main con-
trol valve.

1. LIFT CYLINDER
2. LOWERING CONTROL VALVE
3. TILT CYLINDER
4. TILT CYLINDER RELIEF VALVE
5. TO CARRIAGE
6. REMOTE CONTROL VALVE – LIFT
7. REMOTE CONTROL VALVE – TILT
8. AUXILIARY CONTROL VALVE
9. AUXILIARY SPOOL

10. TILT SPOOL

11. LIFT SPOOL

12. MAIN CONTROL VALVE

A = LIFT PILOT
B = LIFT PILOT

C = LIFT PILOT SUPPLY

E = TILT PILOT

F = TILT SUPPLY

G = TILT PILOT SUPPLY

AC = ACCUMULATOR

AX = AUXILIARY SUPPLY

AY = AUXILIARY SUPPLY

BS = BRAKE SUPPLY

AY = AUXILIARY SUPPLY

CS = COOLING
DA = RETURN
DB = RETURN

HP1 = LIFT SUPPLY
HP2 = LIFT SUPPLY

LS = STEERING PILOT
P1 = MAIN SUPPLY
P2 = MAIN SUPPLY
P3 = PILOT SUPPLY

PB = PARKING BRAKE

SC = STEERING SUPPLY

TB = TILT SUPPLY

TF = TILT SUPPLY

HYDRAULIC LINE CODES

CP4

CP1

CP2

CP1 = LIFT SYSTEM
CP2 = LIFT SYSTEM
CP3 = PILOT SUPPLY
CP4 = STEERING RELIEF
CP5 = LIFT PILOT
CP6 = TILT/AUXILIARY

PILOT

CP7 = ACCUMULATOR
CP8 = PARKING BRAKE

PRESSURE CHECK

PORTS

13. HYDRAULIC TANK
14. HYDRAULIC PUMP
15. PILOT SUPPLY VALVE
16. SERVICE BRAKES
17. PARKING BRAKE CALIPER
18. SERVICE BRAKES
19. INCHING/BRAKE PEDAL
20. BRAKE PEDAL
21. THERMOSTATIC VALVE
22. STEERING CONTROL UNIT
23. STEERING CYLINDER

CP3

CP5

CP6

CP7

CP8

FIGURE 2. HYDRAULIC SYSTEM COMPONENTS

1. MAIN CONTROL VALVE
2. RETURN TO TANK
3. LIFT PILOT SUPPLY
4. CHECK PORT – STEERING
5. AUXILIARY CONTROL

VALVE

6. SUPPLY FROM PUMP
7. CHECK PORT – LIFT

PILOT PRESSURE

8. CHECK PORT – PARKING

BRAKE

9. CHECK PORT– TILT PILOT

PRESSURE

10. CHECK PORT – ACCUMULATOR

11. PILOT SUPPLY VALVE

12. CHECK PORT – LIFT CIRCUIT
13. CHECK PORT – LIFT CIRCUIT

14. TO TILT CYLINDERS
15. TO LIFT CYLINDERS
16. PILOT SUPPLY –

AUXILIARY

17. PILOT SUPPLY – TILT
18. PILOT SUPPLY – LIFT
19. STEERING SUPPLY

MAIN CONTROL VALVE

DESCRIPTION (See FIGURE 3.)

The main control valve controls the flow and pressure of
the oil to the steering, lift and tilt cylinders and the aux-
iliary circuit. The control valve has five spools; one for
steering priority, two to control lifting and lowering and
one each for tilt and auxiliary functions. There are three
relief valves in the control valve. The two relief valves
for the lift circuit are set at 24.1 MPa (3500 psi). The re-
lief valve for the tilt and auxiliary circuits is set at 19.0
MPa (2750 psi). The operation of the priority spool is
controlled by pilot pressure from the steering control
unit. Oil that is not needed for steering flows to the lift
circuit.

Lifting

There are two lift spools that control the oil flow to the
lift cylinders. The pilot lines are connected to both lift
spools, and the spools move at the same time. While one
lift spool receives oil directly from the pump, the other
spool receives oil from the priority valve. The move-
ment of the flow regulator is controlled by a pilot line
from the steering control unit. When oil is not required
for the steering system, the flow regulator allows oil to
flow to the second lift spool. The increased oil flow to
the lift cylinders allows the mast lift speed to increase.

When the lift spools are moved to the lift position, oil
pressure moves the load check valves from their seats.
The oil from the control valve flows to the base of the lift
cylinders through the lowering control valves.

The lines at the top of the lift cylinders are breather lines.
These lines allow for air movement and some oil to lu-
bricate the cylinder rods and bores.

Lowering

When the lift spools are moved to the lowering position,
oil from the hydraulic pumps goes through the control
valve to the tank. Oil from the base of the lift cylinders
flows through the lowering control valves to the main
control valve and back to the tank.

Tilt Spool

The tilt spool controls the direction and quantity of oil to
the tilt cylinders. When the spool is moved to the for-

ward tilt position, oil flows to the bases of the tilt cylin-
ders. Oil from the rod end of each tilt cylinder returns
through the tilt restriction valves, the tilt spool and then
to the hydraulic tank.

When the spool is moved to the backward tilt position
oil flows to the rod ends of the tilt cylinders. Oil from the
base of each tilt cylinder returns to the tilt spool and back
to the hydraulic tank.

NOTE: There is a relief valve at the rod side port of each
tilt cylinder. (See FIGURE 1.) The relief valves are used
to prevent cavitation of the oil when the mast is tilted
forward with a load. Tilting forward with a load can
make the oil in front of the pistons (tilt cylinders) move
too fast. The relief valves prevent oil flow from the rod
side ports until the pressure reaches 14 MPa (2030 psi).
When tilting backward, oil flows past the check valves
in the relief valve housing to the rod side ports.

Priority Valve

The spool for the priority valve controls the oil flow to
the steering system. Oil from one section of the hydrau-
lic pump enters the main control valve at the priority
spool. The movement of the flow regulator spool is con-
trolled by a pilot line from the steering control unit. The
pilot line senses the load in the steering circuit. Oil that is
not used for steering flows to the lift circuit.

Relief Valves

The relief valves set the limit for the maximum pressure
within the hydraulic circuits. The relief valves for the
lift circuit are set at 24.1 MPa (3500 psi). The relief
valve for the tilt and auxiliary circuits is set at 19.0 MPa
(2750 psi).

During normal operation, oil flows around the sides of
the spool for the relief valve. The force of a spring holds
the spool against the seat in the valve body. When the
pressure of the oil reaches the relief setting, the pressure
will push the spool from the seat. The oil flows past the
spool and flows to the drain circuit. The spool stays in
the open position until the pressure is less than the relief
setting.

FIGURE 3. MAIN CONTROL VALVE

14. END SECTION
15. ADAPTER
16. SPRING AND SPACER
17. CAPSCREW
18. SPRING HOUSING
19. SPRING RETAINER
20. PLUG
21. AUXILIARY SECTION
22. TILT/AUXILIARY RELIEF VALVE

1. OUTLET HOUSING
2. AUXILIARY SPOOL
3. O–RING
4. SPOOL HOUSING
5. RETAINER
6. TILT SPOOL
7. TILT SECTION
8. LIFT SECTION
9. LIFT SPOOL

10. LIFT RELIEF VALVE

11. INLET SECTION

12. PRIORITY VALVE

SECTION

13. PRIORITY SPOOL

REPAIRS

NOTE: Most repairs can be made without removing the
hydraulic module. The hydraulic module can be re-
moved from the frame as a unit if necessary.

Removal (See FIGURE 2. and FIGURE 4.)

WARNING

When working on or near the mast, see SAFETY
PROCEDURES WHEN WORKING NEAR THE
MAST in the section PERIODIC MAINTENANCE,
8000 SRM 662.

1. Lower the mast completely. Open the door of the hy-
draulic compartment on the left side of the frame. Clean
the outside of the valve(s).

2. Make sure the hydraulic lines have identification tags.
Disconnect the hydraulic lines at the valve(s) as neces-
sary. Disconnect the main supply and return lines. Put
caps on the open lines.

3. Remove the bolts that fasten the control valve(s) to
the hydraulic module. Remove the valve(s).

Disassembly (See FIGURE 3.)

WARNING

Compressed springs can release with great force.
Wear eye protection and be careful when disassem-
bling valves.

See FIGURE 3. and disassemble the control valve as
necessary. Be sure to keep the parts from each valve sec-
tion together. Also, keep the valve sections in the correct
order.

Cleaning And Inspection

WARNING

Cleaning solvents can be flammable and toxic, and
can cause skin irritation. When using cleaning sol-
vents, always follow the solvent manufacturer’s rec-
ommended safety precautions.

Clean all parts in solvent and dry the parts with com-
pressed air. Keep the spool assemblies separate. Inspect
the spools and bores for damage. Inspect the parts of the
valve assemblies for damage. Replace damaged parts.

Assembly (See FIGURE 3.)

1. Make sure the spools are installed in the same bores
from which they were removed. Lubricate all parts with
hydraulic oil then assemble and install the spools as fol-
lows:

a. Install the O–ring on the adapter. Install the adapt-
er on the spool.

b. Install the spring, spacer and retainers on the
spool. Install the capscrew that holds the spring to
the spool.

c. Install the O–ring and spring housing on the adapt-
er.

d. Install the retainer and capscrews to hold the
spring housing to the valve section.

e. Install the O–ring and spool housing at the other
end of the spool. Install the retainer and capscrews
for the spool housing.

2. Install the flow regulator, spring and retainers.

3. Install the load check valve assemblies. Install the re-
lief valve assemblies.

4. Install the O–rings between the valve sections and in-
stall the sections together. Tighten the nuts on the
through bolts.

Installation (See FIGURE 2. and FIGURE 4.)

1. Install the control valve on the hydraulic module. In-
stall the bolts, washers and nuts.

2. Connect the hydraulic lines to the valve. Check the
identification tags to make sure that the lines are cor-
rectly connected to the ports.

3. Start the engine and operate the valve. Check for
leaks. Check the relief pressure as described in
CHECKS AND ADJUSTMENTS.

CHECKS AND ADJUSTMENTS

Check The Relief Pressures

1. Connect a 28 MPa (4000 psi) gauge to the check ports
for the control valve. See FIGURE 13.

FIGURE 4. HYDRAULIC MODULE

1. MAIN CONTROL VALVE
2. MODULE
3. MOUNT FOR AUXILIARY CONTROL

VALVE

4. MOUNT FOR PILOT SUPPLY VALVE
5. PILOT SUPPLY VALVE
6. AUXILIARY CONTROL VALVE

2. Operate the engine at 2100 rpm. When the oil tem-
perature is 54

to 65

C (130 to 150

F), check the pressur-

es as follows:

a. Operate the lift spool to lift the mast until it stops.
The hydraulic pressure will reach the relief pressure
at this point. The correct relief pressure at check
ports No. 1 and 2 in FIGURE 13. is 24.1 to 24.9 MPa
(3450 to 3550 psi) at 2500 rpm.

b. Operate the tilt spool to tilt the mast backward un-
til it stops. The hydraulic pressure will reach the re-
lief pressure at this point. The correct relief pressure
at check port No. 1 in FIGURE 13. is 18.9 to 19.6
MPa (2700 to 2800 psi) at 2500 rpm.

3. If the relief pressure is not correct, remove the cap and
adjust the relief pressure. Install the cap after adjust-
ments.

MAIN CONTROL VALVE – TROUBLESHOOTING

PROBLEM

POSSIBLE CAUSE

PROCEDURE OR ACTION

Oil leaks from end of spool.

O–rings at spool housing(s) leak.

Retainers for spool housing are loose.

Pilot lines are damaged or leak.

Install new O–rings.

Tighten capscrews for retainers.

Tighten fittings or install new lines.

Spool(s) will not move.

The pressure from the remote control
valve is not correct.

Remote control valve is damaged.

Pressure reduction valve for pilot
supply is damaged or not adjusted
correctly.

Pilot lines are damaged or leak.

Spool does not move freely in bore.

Check pilot pressure. Make repairs as
necessary.

Repair control valve.

Repair or adjust.

Tighten fittings or install new lines.

Repair valve section.

Spool will not return to the
neutral position.

Return spring or springs are
damaged. Capscrew for spring is
loose.

Spool does not move freely in bore.

Install a new spring and tighten
capscrew.

Install new valve section.

Slow or no movement of lift
cylinder(s).

Relief valve(s) is damaged or not
correctly adjusted.

Leaks between spool(s) and bore(s).

Spool(s) not fully extended or
retracted.

Hydraulic pump is damaged.

Restriction in the hydraulic lines.

Load is greater than capacity of the
system.

Damaged load check valve(s).

The pressure from the remote control
valve is not correct.

Check and adjust pressure. Install a
new relief valve.

Install new valve section.

Check that spool moves freely in bore.

Repair pump.

Check and repair hydraulic lines.

Handle correct loads.

Install new check valve(s).

Check pilot pressure. Make repairs as
necessary.

Hydraulic pressure is above
or below specifications.

Relief valve is damaged.

Restriction in the return line.

Check and adjust pressure. Install a
new relief valve.

Check and repair hydraulic lines.

REMOTE CONTROL VALVE

DESCRIPTION

The remote control valve is installed in the console at the
right–hand side of the seat. The remote control valve is
an assembly of two sections with spools and an interme-
diate block. One section controls the lift and lower func-
tions. The other section controls the tilt function.

Each section of the remote control valve has two spool
assemblies that are actuated by a hand lever. The spool
assemblies in a section of the remote control valve direct

pilot oil flow to the spools in the main control valve.
Springs move the spools to close the passages that sup-
ply pilot pressure when the operator releases the hand
lever.

OPERATION
(See FIGURE 5. and FIGURE 6.)

Through the use of pilot pressure, the remote control
valves control the movement of the spools in the main
control valve. The remote control valve assembly re-

ceives its oil supply from the pilot supply valve at 2.8 to
3.2 MPa (400 to 450 psi).

In the neutral position, both spools in a remote control
valve are closed. They will not let the pilot pressure flow
to the main control valve. The spools will, however, let
the oil in the pilot lines flow to the drain circuit.

FIGURE 5. SCHEMATIC,

REMOTE CONTROL VALVE

5. SUPPLY
6. FORWARD TILT
7. LIFT
8. LOWER

1. LIFT/LOWER
2. TILT
3. BACKWARD TILT
4. DRAIN CIRCUIT

DOWN

UP FORWARD

BACK

LETTERS A – G ARE IDENTIFICATION CODES.

When a control lever is moved forward or backward, the
control lever pushes on one of the plungers. The plunger
and guide push the springs and pilot spool down. As the
spool moves down, the passage in the open–center spool
allows oil flow from the inlet port through the open cen-
ter of the pilot spool to one of the pilot lines. The pilot
pressure pushes directly on a spool in the main control
valve. The oil in the opposite pilot line flows through the
center of the spool in the remote control valve and out of
the drain port.

The movement of the spool(s) in the main control valve
is proportional to the movement of the spool in the re-
mote control valve. (The first 3

of lever movement

does not move the spool.) When a hand lever is moved a
small amount, the spool in the remote control valve
moves down and then closes. The spool moves back up
and closes because the pilot circuit is full of oil and this

pressure is sensed at the bottom of the spool. The spool
opens and closes as necessary to keep the correct pres-
sure in the pilot circuit.

(NEUTRAL)

(ACTUATED)

FIGURE 6. OPERATION OF THE

REMOTE CONTROL VALVE

1. CONTROL VALVE LEVER
2. PLUNGER, NEUTRAL POSITION
3. PLUNGER, ACTUATED
4. DRAIN PORT
5. SPRINGS
6. INLET PORT
7. PILOT SPOOL
8. INLET PRESSURE TO PILOT LINE
9. PILOT LINE PRESSURE TO DRAIN

This action keeps the spool(s) in the main control valve
in the position selected by the operator. (The spool can
move down to let pressure in or it can move up to open
the pressure circuit to the drain circuit.)

When the control lever is released, the spool in a remote
control valve returns to the neutral position. The pilot
line is now open to the drain circuit. This action permits
the spool(s) in the main control valve to return to neu-
tral.

REPAIRS

Removal (See FIGURE 8.)

WARNING

When working on or near the mast, see SAFETY
PROCEDURES WHEN WORKING NEAR THE
MAST in the section PERIODIC MAINTENANCE,
8000 SRM 662.

1. Lower the mast completely. Shut off the engine and
apply the parking brake.

WARNING

Before disconnecting any hydraulic lines, release
pressure from the hydraulic circuit as follows:

a. Shut the engine off and completely lower the
carriage.

b. Operate the lift/lower lever and the brake ped-
als until the hydraulic pressure is released.

2. Remove the rear cover from the console. Put tags for
identification on all of the hydraulic lines. Disconnect
the hydraulic lines from the remote control valve. Put
caps on the open lines.

3. Remove the two screws that fasten the cover that
holds the remote control valve. Remove the cover and
the valve as a unit.

4. Remove the capscrews and nuts that fasten the remote
control valve to the cover. Remove the cover from the
valve.

Disassembly (See FIGURE 7.)

1. Put identification marks on the sections of the remote
control valve and the intermediate block.

FIGURE 7. REMOTE CONTROL VALVE

1. VALVE BODY
2. SPRING
3. SPOOL
4. SPRING RETAINER
5. SPACER
6. WASHER
7. SCREW
8. RETAINER
9. PLUNGER

10. GUIDE

11. O–RING

12. SEAL RING
13. LEVER
14. BOOT
15. ACTUATOR
16. PIN
17. ACTUATOR PLATE
18. RETAINER PLATE

2. Remove the nuts and the through bolts that hold the
sections of the valve together.

3. Disassemble a valve section as follows:

a. Remove the rubber boot from the plate. Remove
the pivot pin for the control lever. Remove the con-
trol lever and boot.

b. Put identification marks on the valve body and the
plates at the top of the valve body. Carefully remove
the capscrews that hold the plates to the top of the
valve body. Remove the plates.

c. Remove a pin and guide assembly from the valve
body.

WARNING

Compressed springs can release with great force.
Wear eye protection and be careful when disassem-
bling valves.

d. Carefully remove the spring assembly and the
spool from the same bore in the valve body. Remove
the return spring.

NOTE: Keep the parts from each bore separate. The
parts must be installed in the original bores. The parts
are adjusted with spacers. Make a note of the number
and location of the spacers. Changing the spacers will
affect the operation of the valve.

FIGURE 8. ARRANGEMENT, REMOTE CONTROL VALVE

1. LIFT/LOWER LEVER
2. TILT LEVER
3. TILT PILOT VALVE

12428

BOTTOM

VIEW

A LIFT
B LOWER
C LIFT SUPPLY
D DRAIN

E TILT FORWARD

F TILT BACKWARD

G TILT SUPPLY

4. COVER
5. CONSOLE
6. LIFT PILOT VALVE

e. Repeat steps c and d to remove the second spool.

Cleaning and Inspection

WARNING

Cleaning solvents can be flammable and toxic, and
can cause skin irritation. When using cleaning sol-
vents, always follow the solvent manufacturer’s rec-
ommended safety precautions.

Compressed air can move particles so that they
cause injury to the user or to other personnel. Make
sure that the compressed air path is away from all
personnel. Wear eye protection.

Clean all parts in solvent and dry the parts with com-
pressed air. Inspect the spools and bores for damage. In-
spect the parts of the valve assemblies for damage. Re-
place damaged parts. If there are scratches or other dam-
age, the valve must be replaced. Spools are not available
as separate parts.

Assembly (See FIGURE 7.)

1. Install the return springs in the valve body.

2. Make sure that the same spacers are used with each
spring assembly. Install the spring assemblies and the
spools in the bores. Make sure that the parts are installed
in the same bores from which they were removed.

3. Assemble the guide and plunger assemblies. Install
the O–rings and guides in the valve body.

4. Install the plates at the top of the valve. Tighten the
screws to 5 N.m (44 lbf in). Install the control lever and
the rubber boot. If necessary, tighten the lock nut on the
hand lever to 30 N.m (22 lbf ft).

5. Assemble the valve sections and the intermediate
block. Make sure that the O–rings are in position. Install
the through bolts. Tighten the nuts to 5 N.m (44 lbf in).

Installation (See FIGURE 8.)

1. Use the capscrews and nuts to install the console
cover on the remote control valve. Make sure that the
cover is installed in the correct direction.

2. Install the valve and the cover as a unit. Fasten the
cover to the console with two screws.

3. Connect the hydraulic lines to the sections of the
valve as shown in FIGURE 8.

4. Start the engine and operate the hydraulic system.
Check that all functions of the remote control valve
work correctly.

5. If necessary, check the pressure to the remote control
valve. See Pressure Reduction Valves in this section for
the correct procedure.

6. Install the back cover on the console.

Adjustment (See FIGURE 9.)

When the hand lever is in the neutral position, turn the
adjustment screw (2) to get 0.13 to 0.25 mm (0.005 to
0.010 in) clearance between the plunger (1) and the ad-
justment screw. Tighten the lock nut (3) to 5 N.m (44 lbf
in).

FIGURE 9. LEVER ADJUSTMENT

11788

1. PLUNGER
2. ADJUSTMENT SCREW
3. LOCK NUT

REMOTE CONTROL VALVE – TROUBLESHOOTING

PROBLEM

POSSIBLE CAUSE

PROCEDURE OR ACTION

The cylinders that are
controlled by the remote
control valve do not move, or
move slowly.

A spool or spools in the remote
control valve do not move completely.

Pilot pressure from the pilot supply
valve is not correct.

The pilot lines are damaged or have
leaks.

Check and repair the valve as
necessary.

Check the pressure from the pilot
supply valve.

Install new pilot lines.

PILOT SUPPLY VALVE

DESCRIPTION AND OPERATION
(See FIGURE 10.)

The pilot supply valve controls the flow of oil to the cir-
cuits for the following: remote control valve, brake sys-
tem and the accumulator.

The pilot supply valve has a relief valve, three check
valves, a charging valve, an unloader valve and three
pressure reduction valves. The solenoid that operates
the brake is also installed on the pilot supply valve.

The relief valve limits the pressure from the hydraulic
pump to 21.4 MPa (3100 psi). One check valve keeps oil
in the parking brake circuit. The other check valves keep
oil in lift/lower circuit at the remote control valve.

The pressure reduction valves control the oil pressure to
the remote control valves and the parking brake system.
The circuit for the remote control valves operates at 2.9
MPa (425 psi). The parking brake circuit operates at 6.2
MPa (900 psi).

The charging valve and unloader valve work together to
supply oil to the brake system and the accumulator. The
accumulator lets the operator apply the brakes or lower
the mast when the engine is not running.

The charging valve has a spool, check valve and an un-
loader valve. Oil from the pump enters the charging
valve spool. A relief valve limits this oil to 21.4 MPa
(3100 psi). Oil flows past the charging valve spool to the
accumulator and the pressure reduction valves. The
charging valve stops charging automatically when the
accumulator pressure reaches its high limit of 18.6 MPa
(2700 psi). At this time all of the oil flow goes to the oil

cooler and then to the brake system. When the accumu-
lator pressure reaches its low limit of 14.5 MPa (2100
psi), the unloader valve allows oil from the pump to
charge the accumulator. Two check valves in the circuit
keep oil from flowing out of the accumulator.

REPAIRS
(See

FIGURE 4. and FIGURE 10.)

WARNING

Compressed springs can release with great force.
Wear eye protection and be careful when disassem-
bling valves.

Repairs to the pilot supply valve are limited to replacing
seals and O–rings. The relief valves and other parts must
be replaced as complete assemblies. Do not disassemble
or try to repair any of the cartridges. See CHECKS AND
ADJUSTMENTS to adjust the relief setting.

CHECKS AND ADJUSTMENTS

Check And Adjust The Relief Valve
(See FIGURE 13.)

1. The relief valve has a check port. Connect a 28 MPa (0
to 4000 psi) pressure gauge to No. 3 check port shown in
FIGURE 13.

2. Start the engine. Run the engine until the temperature
of the hydraulic oil is 55

to 65

C (

130

to 150

F).

3. To adjust a relief valve setting, remove the cap. Use an
allen wrench to turn the adjuster screw. Turn the adjuster
screw clockwise to increase the pressure. When the re-
lief pressure is correct, install the cap.

FIGURE 10. PILOT SUPPLY VALVE

13. CHECK VALVE – PARKING BRAKE
14. CHECK VALVE – PILOT SUPPLY
15. LIFT CIRCUIT – PRESSURE

REDUCTION VALVE

16. TILT CIRCUIT – PRESSURE

REDUCTION VALVE

17. PARKING BRAKE – PRESSURE

REDUCTION VALVE

1. PLUG
2. BRAKE SYSTEM SUPPLY
3. FROM LIFT CIRCUIT
4. PILOT PRESSURE FOR TILT
5. PILOT SUPPLY FOR

LIFT/LOWER

6. RELIEF VALVE
7. BRAKE SYSTEM COOLING SUPPLY
8. PARKING BRAKE SUPPLY
9. CHARGING VALVE

10. PARKING BRAKE SOLENOID

11. UNLOADER VALVE

12. CHECK VALVE – LIFT CYLINDER

Check The Pressure Reduction Valves
(See FIGURE 10. and FIGURE 13.)

Each pressure reduction valve has a check port. Check
the pressures as follows:

1. Lower the lift cylinders completely. Connect a 4 MPa
(0 to 600 psi) gauge to check port Nos. 5 and 6 for the 2.9
MPa (425 psi) pressure reduction valves. Connect a 7

MPa (0 to 1000 psi) gauge to check port No. 8 for the 6.2
MPa (900 psi) pressure reduction valve.

2. Start the engine and check the pressure gauge(s).

3. To adjust the pressure setting, remove the cap. Use an
allen wrench to turn the adjuster screw. Turn the adjuster
screw clockwise to increase the pressure. When the re-
lief pressure is correct, install the cap.

PILOT SUPPLY VALVE – TROUBLESHOOTING

PROBLEM

POSSIBLE CAUSE

PROCEDURE OR ACTION

ACCUMULATOR CHARGE VALVE AND ACCUMULATOR

Remote control valve does
not operate correctly.

Accumulator charge valve does not
operate correctly.

Restriction in line to pilot supply valve.

Check pilot pressure ar check ports.

Install new line.

Carriage/attachment functions
do not operate.

Accumulator charge valve does not
operate correctly.

Electrical wires are damaged or
disconnected.

Pressure reduction valve is not
adjusted correctly.

Clean or replace charge valve.

Connect or repair wires.

Check and adjust pressure.

Mast does not lower when the
engine is not running

Accumulator does not operate
correctly.

Accumulator charge valve does not
operate correctly.

Replace accumulator.

Clean or replace charge valve.

PRESSURE REDUCTION VALVES

Remote control valve does
not operate correctly.

Pressure reduction valve is not
adjusted correctly.

Hydraulic line(s) have a restriction.

Accumulator charge valve does not
operate correctly.

Electrical wires are damaged or
disconnected.

Check pilot pressure ar check ports.

Install a new line.

Clean or replace charge valve.

Connect or repair wires.

Carriage/attachment functions
do not operate.

Pressure reduction valve is not
adjusted correctly.

Hydraulic line(s) have a restriction.

Check and adjust pressure.

Install a new line.

Parking brake will not release.

Pressure reduction valve is not
adjusted correctly.

Hydraulic line(s) have a restriction.

Accumulator charge valve does not
operate correctly.

Check and adjust pressure.

Install a new line.

Clean or replace charge valve.

AUXILIARY CONTROL VALVE

DESCRIPTION AND OPERATION

The auxiliary control valve is a solenoid operated valve
that controls the flow of oil from the auxiliary spool in
the main control valve. The operator actuates the auxil-
iary control valve with switches in the operator’s com-
partment. The oil from the auxiliary control valve is
used to move the auxiliary spool in the main control

valve. Oil from the auxiliary spool flows to the selector
valves for the functions at the carriage, such as fork
positioners.

When the operator pushes a switch, one solenoid on the
auxiliary control valve and a solenoid on the selector
valve are energized at the same time. The solenoid on
the auxiliary control valve opens and lets oil flow

through the pilot line to move the auxiliary spool. The
opposite end of the auxiliary spool is open to drain
through the other solenoid on the auxiliary control
valve. When the auxiliary spool moves, it lets oil from
the hydraulic pump flow to the selector valve as re-
quired.

REPAIRS

Removal (See FIGURE 4.)

1. Stop the engine and lower the mast completely. Open
the door for the hydraulic module on the left side of the
frame.

2. Disconnect the electrical wires at the solenoid con-
nectors.

WARNING

Before disconnecting any hydraulic lines, release
pressure from the hydraulic circuit as follows:

a. Shut the engine off and completely lower the
carriage.

b. Operate the lift/lower lever and the brake ped-
als until the hydraulic pressure is released.

3. Put tags for identification on all the hydraulic lines
that are connected to the control valve. Disconnect the
lines at the fittings and put caps on the open lines.

4. Remove the nuts, washers and bolts that fasten the
control valve to the plate.

Disassembly (See FIGURE 11.)

WARNING

Compressed springs can release with great force.
Wear eye protection and be careful when disassem-
bling valves.

1. Make marks on each solenoid and the valve body. The
marks are for alignment during assembly. Remove the
capscrews and one of the solenoids.

2. Remove the parts from the valve body.

3. Remove the other solenoid and parts.

Cleaning And Inspection

WARNING

Cleaning solvents can be flammable and toxic, and
can cause skin irritation. When using cleaning sol-
vents, always follow the solvent manufacturer’s rec-
ommended safety precautions.

WARNING

Compressed air can move particles so that they
cause injury to the user or to other personnel. Make
sure that the compressed air path is away from all
personnel. Wear eye protection.

Use solvent to clean the metal parts. Carefully dry the
parts with compressed air. Inspect the bores for the
spools. Inspect the surfaces of the spools that slide on the
bores. If a bore or a spool has scratches or cracks, re-
place parts as necessary.

Assembly (See FIGURE 11.)

NOTE: Lubricate the parts with clean hydraulic oil and
install new seals during assembly.

1. Install the O–rings and back–up rings on the sleeve.
Install the O–ring on the spacer. Install the sleeve in the
body. Install the spring retainer, spring, cover and
capscrews. Push the other end of the spool so that the
spool moves in the bore. If the spool does not move
freely, replace the direction control valve.

2. Install the spacer, spring and spring guide. Install the
retainer on the shuttle. Install the shuttle.

3. Install the solenoid and capscrews.

Installation (See FIGURE 4.)

1. Install the control valve on the plate.

2. Connect the hydraulic lines. Connect the wires to the
solenoids.

Checks And Adjustments

The auxiliary control valve have no adjustments. See Pi-
lot Supply Valve, Checks and Adjustments in this sec-
tion to check the pilot pressure.

FIGURE 11. AUXILIARY CONTROL VALVE

1. SPACER
2. O–RING
3. SPRING
4. SPRING GUIDE
5. SHUTTLE
6. RETAINER
7. SOLENOID
8. SLEEVE
9. BACK–UP RING

10. VALVE BODY

AUXILIARY CONTROL VALVE – TROUBLESHOOTING

PROBLEM

POSSIBLE CAUSE

PROCEDURE OR ACTION

An auxiliary function does not
operate.

The switch for the function does not
operate correctly.

Solenoid does operate correctly.

Pilot pressure is not correct.

The accumulator charge valve does
not operate correctly.

The pump is damaged.

The lines from the main control valve
to the selector valves have damage.

Selector valve(s) does not operate
correctly.

Check and repair switch or wiring.

Replace solenoid.

Check and adjust pressure.

Repair or replace accumulator.

Repair pump.

Repair lines.

Check and repair valve.

AUXILIARY CONTROL VALVE – TROUBLESHOOTING

All auxiliary functions have
reverse operation.

The lines from the attachment control
valve are incorrectly connected at the
manifold for selector valves.

Connect lines correctly.

One auxiliary function has
reverse operation.

The switch is incorrectly connected to
the solenoids on the pilot valve.

Check wiring.

HYDRAULIC PUMP

GENERAL

The hydraulic pump is a three–section gear pump that is
driven by a power take–off arrangement on the trans-
mission housing. The inlet hose for each pump section is
connected to the hydraulic tank. The three sections of
the pump supply different parts of the hydraulic system.
The smallest section of the pump supplies oil to the pilot
supply valve. The middle section of the pump supplies

oil to the main control valve for the lift, tilt and auxiliary
circuits. The large section of the pump supplies oil to a
steering priority valve in the main control valve.

REPAIRS

Repair information for the pump is in the section HY-
DRAULIC GEAR PUMPS, 1900 SRM 97. See
FIGURE 12. when removing or installing the pump.

FIGURE 12. HYDRAULIC PUMP ARRANGEMENT

1. HYDRAULIC PUMP
2. SUCTION LINE
3. TO MAIN CONTROL VALVE
4. TO MAIN CONTROL VALVE
5. TO PILOT SUPPLY VALVE

SPECIFICATIONS

LABEL FOR HYDRAULIC SYSTEM CHECK PORTS

CHECK PORT

SPECIFICATION

NO. 1 – LIFT SYSTEM RELIEF

24.1 to 24.9 MPa (3450 to 3550 psi) @ 2500 rpm

NO. 2 – LIFT SYSTEM RELIEF

24.1 to 24.9 MPa (3450 to 3550 psi) @ 2500 rpm

NO. 3 – PILOT SUPPLY VALVE RELIEF

21.4 to 22.1 MPa (3050 to 3150 psi) @ idle speed

NO. 4 – STEERING SYSTEM RELIEF

16.5 to 17.2 MPa (2350 to 2450 psi) @ 2500 rpm

NO. 5 – LIFT SYSTEM PILOT PRESSURE

2.8 to 3.2 MPa (400 to 450 psi) @ idle speed

NO. 6 – TILT/AUXILIARY PILOT PRESSURE

2.8 to 3.2 MPa (400 to 450 psi) @ idle speed

NO. 7 – ACCUMULATOR PRESSURE

14.5 to 18.6 MPa (2100 to 2700 psi) @ idle speed

NO. 8 – PARKING BRAKE PRESSURE

6.0 to 6.7 MPa (850 to 950 psi) @ idle speed

Make sure oil is at operating temperature – 54 to 65

C (130 to 150

F).

FIGURE 13. HYDRAULIC SYSTEM CHECK PORTS

Document Outline

INTRODUCTION
- GENERAL
- SYSTEM DESCRIPTION AND OPERATION
MAIN CONTROL VALVE
MAIN CONTROL VALVE-TROUBLESHOOTING
REMOTE CONTROL VALVE
REMOTE CONTROL VALVE-TROUBLESHOOTING
PILOT SUPPLY VALVE
PILOT SUPPLY VALVE-TROUBLESHOOTING
AUXILIARY CONTROL VALVE
- DESCRIPTION AND OPERATION
- REPAIRS
AUXILIARY CONTROL VALVE - TROUBLESHOOTING
HYDRAULIC PUMP
- GENERAL
- REPAIRS
SPECIFICATIONS

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