10.

HYDRAULIC SYSTEM

10.1 STRUCTURE AND FUNCTION

The hydraulic system consists of the hydraulic pump mounted on the engine, the material handling control valves
and cylinders, and the steering priority valve and the power steering cylinder.
HYDRAULIC CIRCUIT - POWER BRAKE MODELS

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10. HYDRAULIC SYSTEM

HYDRAULIC CIRCUIT - STANDARD BRAKE MODELS

Lift height 3.7 m or less

Lift height 4.0 m or more

B2

A2

TILT CYLINDER

LIFT CYLINDER A1

DOWN SAFTY
VALVE

MAIN RELIEF
KL PRE.
2625 psi

13.5 to 17.3 /min G1 P T

KPF
KP
FLOW DIVIDER
PS RELIEF PRE.
1711 psi

BLEEDING VALVE
M
P2 P1

POWER
STEERING
CYLINDER
FILTER 20 m
STRAINER 105 m

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 10. HYDRAULIC SYSTEM

10.2 PERIODIC INSPECTION AND MAINTENANCE CHECK POINTS

10.2.1 HYDRAULIC TANK
Breather
1. Oil leakage Cover
2. Oil level amount
Check with oil level gauge and add oil if necessary.
(Also check for oil contamination)
3. Cleaning of strainer
4. Replacement of line filter

10.2.2 PIPING
1. Cracks, scratches, deterioration or twist of piping
Strainer
2. Oil leakage
3. Loosening of mounting bolt and nut Line filter

10.2.3 PIPING OF WORK EQUIPMENT

1. Cracks, scratches, deterioration or twist of piping
2. Oil leakage
3. Loosening of mounting bolt and nut Drain plug

10.2.4 HYDRAULIC DRIFT OF LIFT CYLINDER AND TILT CYLINDER

1. Load the forks with maximum payload and set the mast
(1) upright, lift the forks approx. 59 in. (1,500 mm) from
the ground. 1
2. Match a straight measure (1) on the piston rod of the lift
cylinder (2) and put the mark (A) for measurement,
3. Match a straight measure (2) on the piston rod of the tilt
cylinder (3) and put the mark (B) for measurement,
H
When measured 3.95 in. (100 mm)/
Hydraulic drift of at fork within 15 min
lift cylinder When measured 1.96 in. (50 mm) /
at cylinder within 15 min A

Hydraulic drift of
1.18 in. (30 mm) / 15 min
tilt cylinder
Adjustment: Replace control valve and cylinder packing

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10. HYDRAULIC SYSTEM

10.2.5 DIRECTIONAL CONTROL VALVE (1)

1. Actuation and oil leakage
2. Looseness of mounting bolt

10.2.6 DIRECTIONAL CONTROL VALVE (2)

Measure relief pressure
1. Install an oil pressure gauge to port (A).
A: Control valve relief pressure measurement port
2. Lift the forks to the maximum lifting height, measure the
oil pressure when the oil is relieved, and check it for spec-
ified level.
Relief set pressure: 2,567 - 2,697 PSI (17.7 - 18.6 MPa)
{180 - 190 kgf/cm2}

10.2.7 SOLENOID VALVE, STEERING PRESSURE PORT

1. Actuation, abnormal noise
2. Abnormal generation of heat
3. Oil leakage

10.2.8 HYDRAULIC PUMP

1. Oil leakage
2. Abnormal vibration
3. Noise
4. Abnormal wear of spline
5. Loosening of mounting bolt

10.2.9 FLOW DIVIDER (FOR P/S)

1. Oil leakage
2. Noise
3. Looseness of mounting bolt
P-port
10.2.10 OIL MOTOR Oil pressure measuring port
RC 1/8
1. Oil leakage
2. Noise
3. Looseness of mounting bolt

10.2.11 LIFT CYLINDER

1. Actuation, oil leakage
2. Dents, cracks, curvature or scratches
3. Looseness of mounting bolt

10.2.12 TILT CYLINDER

1. Actuation, oil leakage
2. Dents, cracks, curvature or scratches
3. Looseness of mounting bolt

10.2.13 REACH CYLINDER

Not applicable for this model

10.2.14 WORK EQUIPMENT CYLINDER

1. Actuation, oil leakage
2. Dents, cracks, curvature or scratches
3. Looseness of mounting bolt

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 10. HYDRAULIC SYSTEM

10.3 TESTING AND ADJUSTING

10.3.1 SERVICE HYDRAULIC TANK

The temperature of the oil is very high immediately after stop operation of the truck. Be sure to start
inspection after it has cooled down completely.

1. Remove the drain plug located at the bottom of the

hydraulic tank and drain the oil into a suitable container. Breather
2. Dispose of the old oil properly. Cover
3. Remove the hydraulic tank cover.
4. Remove the strainer.
5. Clean the strainer with flushing oil.
6. Blow dry compressed air from inside to outside of the
strainer until it is completely dry.
7. Clean the inside of the hydraulic tank.
8. Install and tighten the drain plug.
9. Remove the line filter and replace it with a new one.
10. Install the tank cover.
11. Refill the hydraulic oil through the breather hole. Strainer

8.98 gallons (34 liters) Line filter

12. Check the oil level with the oil level gauge.
13. Start the engine and operate the mast, lifting and tilting
until stroke-end for several cycles to bleed the air.

IMPORTANT
Always be sure to use Komatsu genuine hydraulic oil. Drain plug

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10. HYDRAULIC SYSTEM

10.3.2 TROUBLESHOOTING

Problem Cause Remedy

Add hydraulic oil to the specified level of

Low oil level
No oil available amount.
from gear pump Blocked or clogged suction piping or Clean up immediately. In case of dirty oil,
strainer replace with new oil or filter it.

Excessive wear of bushing at (3), (4), (5)

and (6)
Replace with a new part.
Defective bushing seal (14), packing (15)
and (16), plate seal (20) and backup (21)

No pressure Add pressure to the specified level with pres-

Relief valve with faulty adjustment
available from sure gauge.
gear pump
Repair any loose suction piping.
Add oil to the specified level.
Sucking air Check oil seal at gear pump.
Stop operation until bubble goes out from
tank.

Cavitations caused with damaged suction

Remove dirt from piping or strainer.
piping or clogged strainer

Sucking air because of loosened joint of

Tightening again each joint.
suction piping

Noise from gear Replace with new oil with proper viscosity.
pump Cavitations due to high viscosity of oil Operate forklift truck with proper oil tempera-
ture.

Improper alignment between gear pump

Perform correct alignment.
and shaft from engine

Bubble in hydraulic oil Determine cause and correct.

Defective oil seal (18) of gear pump

Oil leakage from Replace with a new part.
Defective body seal (13)
gear pump
Oil being stuck with dirt Check gear pump again.

Check disassembled parts for damage or discoloration. Wash and clean those parts with light-oil. However, never
soak rubber parts in light-oil. Check all the parts again. Repair or replace them with new ones if necessary.

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 10. HYDRAULIC SYSTEM

10.4 REMOVAL AND INSTALLATION

10.4.1 REMOVE HYDRAULIC PUMP

Allow the hydraulic system to cool to avoid getting burned from hot fluids.

1. Place a suitable container under the pump to catch any spills.

2. Remove the bolts securing the supply line to the pump and disconnect the line.
3. Remove the o-ring from the pump flange and discard it.
4. Loosen the fitting securing the discharge line to the pump and disconnect the line.
5. Remove the bolt securing the pump to the engine.
6. Pull the pump off of the engine mounting flange.
7. Remove the o-ring from the pump flange and remove.

10.4.2 INSTALL HYDRAULIC PUMP

1. Place a new o-ring on the pump mounting flange.
2. Mount the pump to the engine engaging the shaft with the engine PTO.
3. Secure the pump in place with the bolt.
4. Place a new o-ring on the suction line flange.
5. Secure the suction line to the pump with bolts.
6. Secure the discharge line to the pump.

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10. HYDRAULIC SYSTEM

10.5 DISASSEMBLY AND ASSEMBLY

10.5.1 FLOW DIVIDER
FLOW DIVIDER COMPONENTS

2
1

4 5 3

1. Body
2. Spool
3. Bolt
4. Spring
5. O-ring

OUT port

IN port Oil flow rate

control port

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 10. HYDRAULIC SYSTEM

 DISASSEMBLY
1. Loosen the bolt (3) and remove.
2. Remove and discard o-ring (5).
3. Remove the spring (4).
4. Remove the spool (2).

Be careful not to damage the circumference of the spool.

1
NOTE: Before carrying out disassembly, make sure that you
understand the structure of the flow divider and lay
the disassembled parts out in order.
2

• Never use any fluid oil other than alcohol or brake

fluid to wash or clean the parts. In particular, never
use mineral oil such as petroleum and gasoline. If
mineral oil sticks on the rubber parts, they may swell
and become unusable.
• Keep the parts in a clean place to prevent the parts
from dirt or dust after washing.
• Always keep such parts as the cylinder, the piston or
the cup away from any foreign body that may damage
those parts.
4 3

 ASSEMBLY
1. Wash or clean metal parts to be reused with flushing oil or
brake fluid.
NOTE: Always use mineral hydraulic oil to wash or clean
rubber parts. Never use flushing oil and petroleum or
gasoline for rubber parts.
Make sure to prevent the spool (2) circumference
from getting scratched or dirty.
2. Assemble the spring (4) as shown in the diagram on the
right.

2 4

3. Slip new o-ring (5) on the bolt (3).

5 3

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10. HYDRAULIC SYSTEM

4. Tighten the bolt (3) .

torque
3
Bolt: 72 - 79 ft/lbs. (98 - 107 Nm) {10 - 11 kgm}

Be careful not to damage the circumference of the spool.

5. Check to make sure the spool functions smoothly after

assembly.

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 10. HYDRAULIC SYSTEM

10.5.2 HYDRAULIC PUMP

HYDRAULIC PUMP COMPONENTS

3.2/3.5 TON K25 PUMP SHOWN BELOW

Front drive gear

Engaged-gear view

Enlarged Enlarged
view of D view of E

The copper alloy face

comes to gear side.
The face chamfered along outer circumfer-
ence comes to the bottom.

Section A-A Section B-B Section A-A

1. Front body assembly 10. Side plate 19. Seal plate

2. Bushing BR assembly (front pump) 11. Mounting flange 20. Seal Backup
3. Bushing BL assembly (front pump) 12. Body seal 21. Isolation plate
4. Bushing ER assembly (center pump) 13. Bush seal 22. Center plate
5. Bushing EL assembly (center pump) 14. Packing ring R 23. Rear body assembly
6. Front drive gear (front pump) 15. Packing ring L 24. Rear drive gear
7. Driven gear (front pump) 16. Hexagon bolt with flange 25. Rear driven gear
8. Rear drive gear (center pump) 17. Oil seal 26. Bushing ER assembly (rear pump)
9. Driven gear (center pump) 18. Snap ring 27. Bushing EL assembly (rear pump)

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10. HYDRAULIC SYSTEM

 DISASSEMBLY
IMPORTANT
• Clean any dirt stuck on the surface of the pump and the driving shaft, before carrying out disassembly.
• Put the disassembled parts on clean paper or cloth so as to prevent such parts from getting damaged.
• Lay all of the disassembled parts out in order for ease of identification of such parts before disassembly

1. Place the flange side of the hydraulic pump face downward.

2. Clamp the flange (11) with a vise and secure it.
NOTE: Apply any soft material such as wooden piece, aluminum or copper to protect the vise.
3. Remove the flange bolt (16).

When loosening the bolt, be careful not to drop the hydraulic pump from the vise. Always make sure to
loosen the bolt gradually.
Always use a proper tool (wrench) in good condition.

4. Remove the hydraulic pump together with the center plate (22) straight in the direction toward the shaft.
NOTE: If the pump is hard to remove, tap the side of rear body (23) lightly with a plastic hammer.
5. Remove the center plate (22) from the rear pump.
6. Remove the seals (12), (13), (14) and (15) in turn.
7. Pull out the spline of the rear drive gear (24).
8. Remove the bushings (26), (27) and the gears (24) (25) from the rear body.
9. Remove the side plate (10) located at the bottom of the rear body hole.
10. Remove the hydraulic pump from the vise.
11. Hold the pump by hand to prevent dropping and place it on the work stand with the front pump side on facing
upwards.
12. Pull the flange (11) out straight in the direction toward the shaft.
13. Remove the seals (12), (13). (14) and (15) in turn.
14. Pull the spline of the front drive gear (6) up slightly.
15. Remove the flange side bushings of (2) (3) and gears of (6) (7) from the front body (1).
16. Remove the parts located at the bottom of the front body, including the side plate (10), the plate seat (19), the
backup seal (20) and the isolation plate (21).
17. Turn the front body and repeat the steps 12 thru 15 to remove the gears (8) (9), the bushings (4) (5), the side
plate (10), the plate seal (19), the backup seal (20) and the isolation plate (21) in return.
NOTE: If it is hard to remove them, push out the gear end of the rear pump from the bearing hole of the front pump
side.
18. Remove snap ring (18) from flange (11).
19. Remove oil seal (17) with a flat-headed screwdriver “A” in
the direction indicated by the arrow in the diagram. 12 A
20. Lay all the disassembled parts out in order for ease of
assembly.

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 10. HYDRAULIC SYSTEM

 ASSEMBLY
A
21
20
Check to make sure that all the disassembled parts have
been cleaned up and dried with compressed air before
beginning assembly.

1. Put the front body (1) on the work stand facing the front
pump side or the flange side on the top.
2. Install the isolation plate (21) at the body bottom hole.
Then, insert the plate seal (19) and backup seal (20). 19
NOTE: Pay careful attention to the direction of the suction
side (A) and the discharge side (B). B
As for the isolation plate, set the face (C) on the out-
side circumference downward or face it to the bottom
hole side.
21
3. Set the copper alloy surface of the side plate (10) to the
top (the gear side).

4. Insert the side plate (10) to the body bottom hole.

NOTE: Pay careful attention to the direction of the suction A
10
side (A) and the discharge side (B).

Copper alloy
surface B

5. Insert the front drive gear (6) and driven gear (7).
NOTE: Match the gear teeth to each other properly.
Be careful that the front pump has the reversed tooth face.
6. Assemble the bushing (2) and (3).
7. Insert the bushing to the body (1) paying attention to the direction.
8. Assemble the body seal (12), the bushing seal (13) and the packing of (14) (15) respectively.
9. Assemble the flange (11) on top of front body (1).
NOTE: The alignment has been made on the shaft at the factory. Be careful not to damage the hole for the shaft.
10. Hold the flange to prevent the assembled parts from coming out.
11. Reverse the body and secure with a vise.
12. Assemble the parts with the center pump using the same procedures taken in steps 2 and 3 above.
13. Insert the rear drive gear (8) and the driven gear (9).
NOTE: Check to make sure both splines of the rear drive gear (8) and the front drive gear (6) match properly.

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10. HYDRAULIC SYSTEM

14. Insert the bushing (4) and (5) using the same procedure
taken in steps 6 and 7 above.
15. Assemble the body seal (12), bushing seal (13) and the
packing of (14) and (15).
16. Put the rear body (23) on the work stand setting the gear
hole side to the top and insert the side plate (10) in the
hole bottom.
17. Pay attention to the turning direction of the gear.
18. Insert the rear drive gear (24) and the driven gear (25).
19. Insert the bushing of (26) and (27) with the same Front drive gear turning direction
procedure taken in step 5 above.
20. Insert the seal of (12), (13), (14) and (15) in turn with the
same procedure taken in step 6 above.
21. Install the center plate (22) on top of rear body.
22. Install the rear pump assembled with the procedures Suction side
taken in steps 12 through 16 above on the top of the front
body (19).
NOTE: Check to make sure both splines of the rear drive
gear (8) and the front drive gear (6) match properly.
23. Tighten the bolt with the flange.
torque

34 - 36 ft/lbs. 46.1 - 48.6 Nm {4.7 - 5.0 kgm}

Discharge side

Always tighten the bolt with the specified torque.

If tightening torque is greater or smaller than the speci-
fied torque, it may result in damage to the bolt or cause trouble blowing the hydraulic oil out from the
matching face of the hydraulic pump.

24. Remove the pump from the vise and assemble the flange
(11) with the oil seal (17) and the snap ring (18).
Gear shaft 18
NOTE: Apply a thin layer of clean lithium grease to the oil
seal. Dust lip
See the direction for installing the oil seal (17).
When installing the oil seal with compressor, make
sure to install it straight so as not to damage the lip.
Protect the front drive gear end with tape to prevent Inside pump Shaft end
the lip from getting damaged and remove the tape
after installation.
25. Turn the drive shaft end with a tool. Lip
NOTE: If it turns lightly by hand, you can assume it is clean 17
internally. If it does not turn easily, carry out disas-
sembly and assembly again because either dirt or bit
of seal could be causing the problem.
26. Install the pump on the truck.
Pay attention to the following points:
• Check to make sure that no scratches can be found at the in-line boss part, which is a standard for
alignment.
• Check to make sure that neither scratches nor dirt can be found on the fitting surface of flange (11). In
particular, carefully check after tightening too strongly with the vise.
• Check to make sure that neither scratches nor dirt can be found on the flange face of the piping.
NOTE: Remove scratches or dirt with fine oilstones.

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 10. HYDRAULIC SYSTEM

10.6 HYDRAULIC PUMP MAINTENANCE STANDARD

HYDRAULIC PUMP MAINTENANCE STANDARD

Front drive gear

Engaged-gear view

Enlarged Enlarged
view of D view of E

The copper alloy face comes to

The face chamfered along outer circumference gear side.
comes to the bottom.

Section A-A Section B-B Section C-C

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10. HYDRAULIC SYSTEM

1. Front Body and Rear Body

The Gear pump is designed to have gear tooth tip contact
the inner wall of gear hole when rotating for improvement
in pump efficiency. Therefore, the contact mark of the
tooth tip (A) can be seen around the suction port of the
pump, if it was ever operated. If the contact mark (A)
covers less than half of the inner wall of gear hole, then it A
is normal. It is also normal that the depth (a) of contact
mark (A) is approximately .002 in. (0.05 mm). When such
depth (a) is more than .006 in. (0.15 mm), replace with a
new gear pump assembly.

2. Drive Gear and Driven Gear

The gear shaft and gear side face should have a smooth
surface if hydraulic oil is clean. However, if your fingernail a
can catch on any rough surface either on the gear shaft
or the gear side face, and also if abnormal wear of the
tooth face can be seen, replace with a new one.

Suction
chamber

When diameter of the shaft (b) is less than .7100 in.

(18.035 mm), replace with a new gear assembly.

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 10. HYDRAULIC SYSTEM

3. Bushing
An ideal bushing condition is when the inside diameter
d
sliding section of the bushing has no rough surface and
shining contact can be seen in half of the suction side. It
is normal if the side face contact (D) is strong at suction Inlet
side showing dark gray color while contact at high
pressure side is weak and quite minimal.
Replace with a new part for the following conditions
described below: c Outlet
• The contact can be seen all over the inside diameter D
sliding surface of the bushing and your fingernail can
catch rough surfaces on it.
• Many scratches can be seen toward circumference at
the bushing side face and your fingernail can catch
rough surfaces on it.
• The scoring marks of a foreign body can be seen at the inside diameter sliding surface and side surface of
the bushing.
Each repair limit size for the bushing are as follows:
If sizes (c) or (d) exist, replace with a new bushing assembly together with a new gear.

Inside diameter (a) Overall length (b)

Type
in. (mm) in. (mm)

For center pump and rear c >.7528 d <.5814

pump (4), (5), (26) and (27) (19.123) (14.768)

c >.7528 d < 1.039

For front pump (2) and (3)
(19.123) (26.411)

4. Side Plate
It is normal if the sliding surface (copper alloy) contact (D)
of the side plate is strong at suction side while such D
contact is weak at high-pressure side.
• If many scratches can be seen toward circumference
and your fingernail can catch in them, replace with a A
new one.
• If the thickness of the side plate is less than .0767 in.
(1.95 mm), replace it with a new one.

Make sure to replace such parts as push seal, body seal,

B
packing ring, plate seal, backup, oil seal and snap ring
with new parts after disassembly.

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