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Takeuchi compact excavator TB125, TB135, TB145 / diesel TNE / diesel Yanmar. Service Manual - page 21

IV-60

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

3. Remove the spring (1), spring holder (2) and

spool (3).

4. Take out the cap screws and remove the cover (4).

• Cap screw tightening torque:

5.8~6.8 N·m (0.6~0.7 kgf·m)

5. Remove the O-ring from the section.

6. Take out the filter (5) and remove the O-ring from

the filter (5).

G4D230

G4D231

IV-61

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

INSPECTION AND ADJUSTMENT

Checking the Parts

Adjusting the Main Relief Valve Pressure

1. Install a pressure gauge in the following pressure

sensor port.
• Control valve pressure sensor port.

“II. Specifications, Standards for Judg-
ing Performance”

2. Run the pump at the rated speed.
3. Operate the control valve’s cylinder spool over its

full stroke and read the value indicated by the
pressure gauge.

4. Turn the set screw (1) while watching the pres-

sure gauge to adjust.
Turning it to the right increases the set pressure.
Turning it to the left decreases the set pressure.

5. After completing the pressure adjustment, tighten

the lock nut (2) while holding the set screw (1) so
it won’t turn.
Operate the relief valve again and check if the
pressure is stabilized.

Parts

Judgment Criteria

Treatment

• Replace

Housing,
Section Body

• Scratches, rust, corrosion of the portion which slides

against the spool.

• Scratches, rust, corrosion of the seal pocket portion of

the part that enters the spool.

• Scratches, rust, corrosion of the port seal portion which

is in contact with the O-ring.

• Scratches, rust, corrosion of the seal portion of the relief

valve, etc.

• Other damage which could be a hindrance to correct

function.

• Scratch marks like being clawed around the outer cir-

cumference sliding portion.

• Scratches on the portion that slides against the seals on

both ends.

• Spool not operating smoothly.
• Imperfect sealing due to damage to the valve or spring.
• Does not catch, but operates lightly when inserted in the

section body and operated.

• Rust, corrosion, deformation, breakage or other marked

damage to the spring, holder or cover.

• Oil leaking to the outside.
• Rust, corrosion or deformation of the seal holder.
• External rust, damage.
• Damage to valve seat contact surface.
• Damage to poppet contact surface.
• Abnormality in the spring.
• O-rings, backup rings, seals

• Replace

• Repair or replace.
• Repair or replace.
• Normal

• Replace

• Repair or replace.
• Repair or replace.
• Replace
• Replace
• Replace
• Replace
• As a rule, all these

should be replaced.

Spool

Load Check Valve

Around Springs

Around Spool Seal

Main Relief Valve,
Port Relief Valve,
Anti-Cavitation Valve

G4B0231

< TB125,TB135 >

IV-62

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

TROUBLESHOOTING

The following items are a list of all the problems that
might occur individually, but in actual practice, 2 or
3 of these problems might occur simultaneously to

compound the trouble. It is therefore desirable to
proceed so that the causes can be eliminated one at a
time.

Symptom

Probable Causes

Remedy

• Replace with a new part.

• Repair or replace the spool.

• Return to the correct shape and check

for eccentric wear of the seal lip.

• Remove paint with paint thinner or re-

move it mechanically. However, at this
time, be careful not to damage the spool
surface or the seal lip.

• Eliminate the factors causing excessive

flow resistance.

Oil leaks from spool seal. • Seal is scratched or the seal lip is worn

due to long use.

• Spool’s seal sliding portion was dam-

aged by some external cause (bruise,
scratch, etc.).

• Seal bulged out and the cover was in-

stalled in a warped state.

• Paint adhered to the sliding portion of

the spool’s seal portion during painting.

• Tank circuit’s pressure became high

and exceeded the pressure level that the
seal was capable of withstanding.

• Foreign matter is biting into the spool’s

sliding surface.

• Oil film between the spool and body

disappears due to abnormally high oil
temperature.

• Lubrication is improper due to deterio-

rating oil.

• Spool is worn from long use or due to

pressure bearing on one side only.

• Spool is bent from externally applied

pressure.

• Entire valve is strained due to strain in

the installation face.

• Valve was used at a pressure or a flow

volume which was out of specification.

• Bolts used to assemble the valve were

tightened excessively.

• Oil is accumulating in the cover (the

side with a spring or a detent) opposite
the side where the spool operates.

• Overhaul and repair or replace.

• Use some method to lower the oil tem-

perature or if the relief valve is operat-
ing frequently, investigate the cause
and reduce the frequency.

• This could be alleviated by simply re-

placing the hydraulic oil, or it could
require an overhaul of the circuit.

• Check the spool’s diameter and con-

sider the necessity of replacement.

• Check the spool’s straightness and other

factors, then repair or replace.

• Loosen the installation bolts, then cut

the installation face and edge and check.

• In the case of pressure, check with a

pressure gauge. In the case of flow
volume, check by the actuator’s speed
of movement and the capacity.

• Check if the assembly bolts are tight-

ened to the specified torque. If the torque
deviates markedly from the specified
torque, tighten them again.

• The spool is leaking oil, so when the

spool moves, oil leaks from the cover.
After confirming this, replace the seal.

• Foreign matter is biting into the load

check valve seat or large scratches were
made by foreign matter biting into the
valve's seat previously.

• Disassemble and check, then overhaul

or replace.

Spool’s sliding is not
smooth.

Cylinder drops while
shifting to a lift operation.

IV-63

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

• Check if it isn't just the cylinder’s natu-

ral drop when the cylinder is held. If the
problem is in the cylinder, disassemble
and repair it.

• Replace the spool or replace the valve

block assembly.

• Manually Operated :

Check if there is something interfering
with the link mechanism.
Pilot Operated:
Check the pilot pressure.

• Disassemble and check, then overhaul

or replace.

Symptom

Can’t be held in the spool
neutral position (cylinder
drops).

• Could be mistaken for a great amount of

leakage in the cylinder.

• The gap between the spool and body is

large, so the amount of oil leaking from
the spool is great.

• Spool won’t return completely to the

neutral position.

• Foreign matter is biting into the port

relief valve seat or the anti-cavitation
valve seat and oil is bypassing. Or a seat
is damaged.

Probable Causes

Remedy

• Foreign matter is biting into the relief

valve seat and oil is bypassing. Or the
seat is damaged.

• The relief valve’s adjustment screw is

loose.

• Foreign matter is biting into the port

relief valve seat or the anti-cavitation
valve seat and oil is bypassing. Or a seat
is damaged.

• Spool stroke is not the specified stroke.

• Pump is damaged and no oil is dis-

charged.

• Disassemble and check, then overhaul

or replace.

• Try tightening the adjustment screw. If

it is loose, correct the setting and tighten
the lock nut securely.

• Disassemble and check, then overhaul

or replace.

• Manually Operated:

Check if there is something interfering
with the link mechanism. Check if a pin
or a pin hole in the link connection is
worn.
Pilot Operated:
Check the pilot pressure.

• Check if the pump is abnormal or not. If

the pump is bad, replace it. Check if the
cause of the abnormality is air being
sucked in, deterioration of hydraulic oil
or shafts not centered, etc.

• The load is too heavy.

• Mechanical resistance of connecting

parts is great regardless of the hydraulic
pressure in the operating unit.

• A large piece of foreign matter is trapped

in the circuit or a pipe is bent, causing
great resistance.

• Compare with an object of the specified

weight.

• Check and replenish hydraulic oil, etc.,

modify or repair.

• Find the affected place and repair it.

The load won’t move.
(Pressure won’t increase.)

Load doesn’t move. (Pres-
sure rises.)

IV-64

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

Symptom

Probable Causes

Remedy

• Check if there is something interfering

with the link mechanism. Check if a pin
or a pin hole in the link connection is
worn or not.

Load doesn’t move. (Pres-
sure rises.)

• Spool stroke is not the specified stroke.

IV-65

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

CONTROL VALVE (TB145)

CONSTRUCTION

1. Inlet Housing
2. Boom Block Assembly
3. Bucket Block Assembly
4. Left Travel Block Assembly
5. Auxiliary Block Assembly
6. Right Travel Block Assembly
7. Swing Block Assembly
8. Arm Block Assembly
9. Outlet Housing
10. Dozer Blade Block Assembly
11. Slew Block Assembly

12. Inlet Housing
13. Port Relief Valve
14. Plug Assembly
15. Anti Cavitation Valve
16. Port Relief Valve
17. Main Relief Valve
18. Tie Rod
19. Nut
20. Main Relief Valve
21. Switch Valve

IV-66

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

Left Travel Block

Right Travel Block

Swing Block

1. Screw
2. Spring Holder
3. Spring
4. Cover
5. Seal Holder
6. Backup Ring
7. O-ring
8. Poppet
9. Spring

K3D201

K3D202

6 7

K3D203

IV-67

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

Boom Block

Slew Block

Arm Block

1. Cover
2. Screw
3. Spring Holder
4. Spring
5. Cover
6. Poppet
7. Spring
8. O-ring
9. Spring Holder

1. Cover
2. Screw
3. Spring Holder
4. Spring
5. Cover
6. Poppet
7. Spring
8. O-ring
9. Poppet
10. Poppet
11. Spring Holder

K3D204

K3D205

K3D206

IV-68

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

Bucket Block

Dozer Blade Block

Switch Valve

1. Cover
2. Screw
3. Spring Holder
4. Spring
5. Cover
6. Poppet
7. Spring
8. O-ring
9. Spring Holder
10. Poppet

1. Cover
2. Screw
3. Spring Holder
4. Spring
5. Seal Holder
6. Poppet
7. Spring
8. O-ring
9. Backup Ring

1. Cover
2. Screw
3. Spring Holder
4. Spring
5. Cover
6. Spring Holder
7. O-ring
8. O-ring

K3D207

K3D208

K3D209

6 8

IV-69

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

Auxiliary Block

Main Relief Valve

Port Relief Valve

1. Cover
2. Screw
3. Spring Holder
4. Spring
5. Cover
6. Poppet
7. Spring
8. O-ring
9. Spring Holder

1. Housing
2. Plug
3. Sleeve
4. Main Poppet
5. Piston
6. Needle Valve
7. Set Screw
8. Washer
9. Lock Nut

10. Spring
11. Spring
12. O-ring
13. Backup Ring
14. O-ring
15. O-ring
16. O-ring
17. Washer

1. Housing
2. Plug
3. Sleeve
4. Main Poppet
5. Piston
6. Needle Valve
7. Spring
8. Spring
9. Set Screw
10. Washer

11. Lock Nut
12. O-ring
13. Backup Ring
14. O-ring
15. Backup Ring
16. O-ring
17. O-ring
18. Wave Washer
19. O-ring

K3D210

IV-70

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

Anti-Cavitation Valve

1. Housing
2. Plug
3. Poppet
4. Poppet
5. Piston
6. Spring
7. O-ring

8. Backup Ring
9. O-ring
10. Backup Ring
11. O-ring
12. O-ring
13. Wave Washer

K3D211

IV-71

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

OPERATION

When the Spool is in the Neutral Position
When the control valve spool is not moving, hydrau-
lic oil flows through the center bypass passage (1) and
then through the tank passage (T) in the arrow direc-
tion, returning to the tank.

When the Spool is Actuated
Explanation is given for the case where the spool is
moved to the right.
When the spool (2) is moved to the right, the center
bypass passage (3) is closed and hydraulic oil entering
from the pump passes through the load check valve
(5) from the parallel passage (4), flowing from the A
port to the actuator. On the other hand, oil returning
from the B port flows through the tank circuit (T) and
returns to the tank.

Load Check Valve
A load check valve (5) is included in each section
except the travel (right, left) sections.
This valve prevents oil from flowing backward due to
the load pressure (C) from the actuator port during
switching of the spool.

IV-72

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

Main Relief Valve

A main relief valve is mounted between the pump
circuit and tank circuit of each inlet housing and
serves to maintain the circuit pressure at the set value.

When the Relief Valve is NOT Operating
When the pressure in the circuit is low with respect to
the set value, the relief valve maintains equilibrium.
Hydraulic oil from the pump passes through the
orifice from chamber (C) and arrives at the spring
chamber (D) and the needle valve (1). On the other
hand, forces F and F1 are acting in the respective
arrow directions on both sides of the main poppet (2).
F = P

Fl = P

P: Pressure A, A1: Cross Sectional Area
Since the cross sectional area of A is less than that of
A1, the main poppet (2) is pushed by the force
“F1 - F” to the seat surface on the left side.

When the Relief Valve is Operating
If the circuit's pressure becomes greater than the set
value of the spring (3), the needle valve (1) is pushed
to the right by hydraulic pressure and oil flows to the
tank passage (T). When this happens, a pressure
differential is generated between the two ends of
orifice of the main poppet (2), and this hydraulic
pressure pushes the main poppet toward the right. As
a result, the pressurized oil in the circuit flows to the
tank passage.
This operation maintains the pressure in the circuit at
the set value.

IV-73

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

Port Relief Valve

Relieving Operation
When the pressure in the circuit is low with respect to
the set value, the relief valve is maintained at equilib-
rium. Pressure from the pump passes from chamber B
to the orifice in piston (4), then reaches chamber C and
the needle valve (5). On the other hand, forces F and
F1 are acting in the arrow directions on both sides of
the main poppet (6).
F = P

F1 = P

P: Pressure A, A1: Sectional Area
Since the sectional area of A is less than that of A1, the
main poppet (6) is pushed by the force “F1-F” to the
seat surface on the left side.

If the pressure in the circuit becomes higher than the
force of the spring (7), the needle valve (5) is pushed
to the right by hydraulic pressure, opening. Oil then
flows around the circumference of the needle valve
(5) and passes through the slits, flowing into the tank
passage (T).

When the needle valve (5) opens, the pressure drops
on the back side of the piston (4), pushing the piston
(4) to be pushed to the right, seating with the needle
valve (5). This shuts off the flow of hydraulic oil to the
rear of the main poppet (6). As a result, the pressure
in chamber C on the inside drops.

Compared to the chamber B side, the pressure in
chamber C is low and there is no equilibrium in
pressure. For this reason, the main poppet (6) opens
and pressurized oil flows to the tank passage (T).

IV-74

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

Suction Operation
When the cylinder is operated at high speed, and the
supply of oil cannot keep up with it, creating a vacuum
in chamber B, oil is supplied from the tank side,
preventing the occurrence of cavitation.
When the pressure in chamber B is lower than the
pressure in the tank passage (T), the differences in the
sectional areas A and A1 cause the main poppet (6) to
open. Thus, sufficient oil from the tank passage (T)
enters chamber B, filling the empty space.

Anti-Cavitation Valve

The anti-cavitation valves are incorporated between
the cylinder ports of the swing and bucket sections
and the tank circuit. When a cylinder is operated at
high speed and when the supply of hydraulic oil can't
keep up with it, causing a vacuum to form at the
cylinder port, this valve supplies oil from the tank,
preventing cavitation from occurring. In the normal
cylinder port, pressure is brought to bear, so the
poppet (1) is closed. If a vacuum is generated at the
cylinder port (P) and the pressure in the tank passage
(T) drops as a result, it pushes on the poppet (1) and
oil flows from the tank passage to the cylinder port.

K3D212

IV-75

HYDRAULIC UNITS

CONTROL VALVE

TB125, 135, 145

Switch Valve

The switch valve is actuated only when the travel
motor and hoe attachment are operated simultaneously.
When the Switch Valve is Actuated
When the spool of the hoe attachment is switched to
block the pilot passage (1) connected to the tank
passage, the pressure in the pilot chamber (2) is
preserved.
This switches the spool (3) to let the oil from the pump
P3 flow into the passages (4) and (5) through the notch
provided on the spool (3). As the passage (4) is
connected to the boom and bucket block while the
passage (5) is connected to the auxiliary block and
swing block, the hoe attachment can be operated
(except for arm operations) while the machine is
traveling.

When the Switch Valve is NOT Actuated
The pilot passage (1) is opened to the tank passage,
making the pressure in the pilot chamber (2) equal to
that in the tank, and the spool (3) is not switched.
Therefore, the oil that has flowed into the switch valve
from the pump P3 returns to the tank from the passage
(6) through the center bypass passage of the arm
block.

K3D213

P3 P4

K3D214

P3 P4

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