Takeuchi compact excavator TB125, TB135, TB145 / diesel TNE / diesel Yanmar. Service Manual

IV-92

HYDRAULIC UNITS

PILOT VALVE

TB125, 135, 145

Secondary pressure doesn’t
rise

• Primary pressure is insufficient
• Spring is damaged or permanently

deformed

• The clearance between the spool and

casing is abnormally large

• There is looseness in the handle

• Keep the primary pressure
• Replace the spring

• Replace the spool and casing assem-

bly

• Disassemble and reassemble, or re-

place the handle

TROUBLESHOOTING

Symptom

Probable Causes

Remedy

• Sliding parts are catching
• Tank line pressure fluctuates

• Air gets mixed into the piping

• Repair or replace
• Remove the abnormal portions of the

tank line

• Operate the machine several times

and bleed out the air

• Tank line pressure is high

• Sliding parts are catching

• Remove the abnormal portions of the

tank line

• Repair or replace

Secondary pressure doesn’t
stabilize

Secondary pressure is high

IV-92-1

HYDRAULIC UNITS

PILOT VALVE

TB125, 135, 145

1. Casing
2. Plate
3. Spool
4. Plug
5. Push Rod
6. Push Rod
7. Seal
8. O-ring
9. Spring Seat

PILOT VALVE

(TB125 : S/N 12514526~, TB135: S/N 13514051~, TB145: S/N 14513261~)

CONSTRUCTION

10. Spring Seat
11. Washer 2
12. Spring
13. Spring
14. Spring
15. Spring
16. Joint
17. Disc
18. Adjusting Nut

IV-92-2

HYDRAULIC UNITS

PILOT VALVE

TB125, 135, 145

OPERATION

The pilot valve casing contains a vertical shaft hole
with a reducing valve incorporated into it. When the
handle is tilted, the push rod and spring seat are
pushed down changing the secondary pressure spring’s
pressure.

The casing provides the inlet port P (the primary
pressure) and the tank port T. The secondary pressure
commensurate with the variation of the operation
angle of the handle (1) is taken out through the output
ports A and B below the vertical shaft hole. The
secondary pressure functions as the pilot pressure to
actuate the spool of the control valve (2).

When the Handle (1) is at the Neutral Position:

The force of the spring (3) for setting the secondary
pressure that determines the output pressure of the
pilot valve is not conveyed to the spool (4). Therefore,
the spool (4) is pushed up by the return spring (5), and
the output ports A and B are connected with the tank
port T, making the pressures in the ports A and B equal
to the pressure in the tank port T.

When the Handle (1) is Tilted:

When the handle (1) is tilted and the push rod (6) is
pushed, the spool (4) moves downward and the input
port P is connected with the output port A. Then, the
oil from the pilot pump flows into the output port A,
generating a pressure.

When the Handle (1) is Kept at a Certain Position:

When the pressure in the output port A increases to the
level equivalent to the force of the spring (3) set by
inclination the handle (1), the hydraulic pressure
balances with the spring force. When the pressure in
the output port A becomes higher than the set spring
force, the output port A and the input port P close
while the output port B and the tank port T open.
When the pressure in the output port A becomes lower
than the set spring force, the output port A and the
input port P open while the output port B and the tank
port T close. Thus, the secondary pressure is always
kept constant.

IV-92-3

HYDRAULIC UNITS

PILOT VALVE

TB125, 135, 145

DISASSEMBLY AND ASSEMBLY

Table of Special Tools

General Cautions

• Since all parts in the pilot valve are precision

machined, carry out disassembly and reassembly
operations in a clean place and take special care not
to scratch the parts.

• Before disassembly, clean the outside surfaces of

the pilot valve.

• Clean each of the disassembled parts and apply

clean hydraulic oil to them.

NAME, DIMENSION

Q’ty

NAME, DIMENSION

Q’ty

INSTALLATION JIG (A)

INSTALLATION JIG (B)

MATERIAL A; S45C
MATERIAL B; SCM415N WITH CEMENTATION HARDENING

MATERIAL B; SCM415N WITH CEMENTATION HARDENING

• Replace all seals with new ones each time the pilot

valve is disassembled.

• During assembly, remove all the foreign matter

from each part and check them to make sure there
are no burrs, bruises using or other marks on them.
Remove all burrs and bruises using an oil stone.

• Apply thin coating of grease to seals when assem-

bling them.

Disassembly

1. Remove the lock nut and the adjust nut (1), then

remove the disc (2).
• Using copper or lead plates, fasten the valve in

a vise.

2. Remove the joint (3), then remove the plate (4).

• Use installation jigs (A) and (B).

IV-92-4

HYDRAULIC UNITS

PILOT VALVE

TB125, 135, 145

3. Take out the plug (5) then remove the push rod (6)

from the plug (5).
• If the plug is difficult to remove, use (–) screw

driver to remove it.

• Be careful not to let the plug fly out from the

spring’s force.

4. Remove the O-ring (7) and seal (8) from the plug.

5. Remove the reducing valve (12) and spring (13).

• Make match marks on the reducing valve and

casing hole so they can be placed in the same
position when they are reassembled.

6. Disassemble the reducing valve.

a. Push in the spring sheet (14) to contract the

spring (15), and move the spool (17) from the
small hole to the large hole of the spring sheet
(14).
• Do not push in the spring sheet too far (at

most 6 mm).

IV-92-5

HYDRAULIC UNITS

PILOT VALVE

TB125, 135, 145

b. Remove the spring seat (14), spring (15) and

washer 2 (16) from the spool (17).

Assembly

1. Assemble the reducing valve (12).

a. Install the washer 2 (16), spring (15) and spring

seat (14) on the spool (17).

b. Push in the spring sheet (14) to contract the

spring (15), and move the spool (17) from the
large hole to the small hole of the spring sheet
(14).
• Do not push in the spring sheet too far (at

most 6 mm).

IV-92-6

HYDRAULIC UNITS

PILOT VALVE

TB125, 135, 145

2. Install the spring (13) and reducing valve (12).

• Install them in the positions they were in be-

fore disassembly.

3. Install the O-ring (7) and seal (8) in the plug (5).

4. Install the push rod (9) in the plug (5).

• Apply hydraulic oil to the push rod.

5. Install the plug (5) and plate (4), then install the

joint.
• Use installation jigs (A) and (B) to install the

joint.

Joint: 47.1

2.9 N·m

IV-92-7

HYDRAULIC UNITS

PILOT VALVE

TB125, 135, 145

6. Install the disc (2), the adjust nut (1) and the lock

nut.
• Tighten the adjust nut to the point where all 4

push rods are uniformly making contact.

• During tightening, the disc should not be

moved.

Adjust Nut: 68.6

4.9 N·m

7. Apply grease to the contact surfaces of the joint

rotating portion, the disc and the push rod.

IV-92-8

HYDRAULIC UNITS

PILOT VALVE

TB125, 135, 145

INSPECTION AND ADJUSTMENT

Checking the Parts

Parts

O-ring



• Replace

Judgment Criteria

Treatment

Seal
Spool



• Wear on sliding portions is 10

m or greater compared to non-

sliding portions

• Scratches on sliding portions
• Spool doesn’t move smoothly

• Replace
• Replace

• Replace
• Repair or replace

Push Rod

• Front end is worn 1 mm or more

• Scratches in the sliding portion

• Replace

Plug

• Seal is imperfect due to damage

• Repair or replace

Operating Portion • Tightening is loose at the pin, shaft or joint of the operating

portion, with looseness of 2 mm or greater

• Due to wear, etc. tightening is loose at the pin, shaft or joint

of the operating portion, with looseness of 2 mm or greater

• Tighten to the specified

torque

• Replace

Casing, Port Plate • Scratches, rust or corrosion on the spool and sliding portion

• Scratches, rust or corrosion on seal portions which come in

contact with the O-ring

• Replace
• Repair or replace

IV-92-9

HYDRAULIC UNITS

PILOT VALVE

TB125, 135, 145

TROUBLESHOOTING

Symptom

Probable Causes

Remedy

Secondary pressure
doesn’t rise

• Primary pressure is insufficient
• Spring is damaged or permanently de-

formed

• The clearance between the spool and

casing is abnormally large

• There is looseness in the handle

• Keep the primary pressure
• Replace the spring

• Replace the spool and casing assembly

• Disassemble and reassemble, or replace

the handle

Secondary pressure
doesn’t stabilize

• Sliding parts are catching
• Tank line pressure fluctuates

• Air gets mixed into the piping

• Repair or replace
• Remove the abnormal portions of the tank

line

• Operate the machine several times and

bleed out the air

Secondary pressure is
high

• Tank line pressure is high

• Sliding parts are catching

• Remove the abnormal portions of the tank

line

• Repair or replace

IV-92-11

HYDRAULIC UNITS

PILOT VALVE

TB125, 135, 145

PILOT VALVE (SWING)

CONSTRUCTION

1. Casing
2. Cover
3. Plug
4. Seal
5. O-ring
6. Push Rod
7. Shim
8. Spool

9. Spring Seat
10. Washer
11. Spring
12. Spring
13. Shaft
14. Bushing
15. Cam
16. Ball

L3D350

IV-92-12

HYDRAULIC UNITS

PILOT VALVE

TB125, 135, 145

OPERATION

“IV-92-2”

DISASSEMBLY AND ASSEMBLY

General Cautions

“IV-92-3”

The following describes the disassembly procedure.
For assembly, refer to the construction diagram and
follow the disassembly procedure in the reverse or-
der.

Disassembly

1. Remove the boot from the cover.

• Use a copper or iron sheet to fasten the valve to

the vice.

• Apply grease to the cam and push rods.

2. Remove the set screw.

Set screw: 6.9 N·m

• Apply Loctite #241 to the set screw.

3. Remove the cam pin, then remove the cam (1).

L2D301

L2D302

L2D303

IV-92-13

HYDRAULIC UNITS

PILOT VALVE

TB125, 135, 145

L2D304

L2D306

4. Loosen the cap screws and remove the cover (2).

• The cover and plug will rise from the surface if

the rebound spring is too strong, so loosen the
cap screws alternately so that the cover is flat.

• Mark the cover and casing so that they can be

reassembled in the same positions.

Cap screw: 8.8 N·m

5. Remove the push rods (4) together with the plug

(5).

6. Remove the O-rings and seal (6) from the plug.

7. Remove the spool assembly (7) and spring (8)

from the casing.
• Never disassemble the spool assembly as the

pressure has been adjusted by the shim.

L3D351

L3D352

IV-92-15

HYDRAULIC UNITS

SHUT-OFF VALVE

TB125, 135, 145

SHUT-OFF VALVES

CONSTRUCTION

Differential Pressure Detection (TB145: For Boom Cylinder Only)

1. O-ring
2. Stem
3. O-ring
4. Backup Ring
5. Lock Nut

Takeuchi compact excavator TB125, TB135, TB145 / diesel TNE / diesel Yanmar. Service Manual - page 23