Vehicle Systems Disassembly & Assembly 21
Washing, Inspection
Wash all parts with clean mineral oil. Dry with
compressed air for inspection.
1. The poppet seats and plugs must be free from
defect and smooth.
2. Main poppet and unload valve must be able to
reciprocate lightly and smoothly.
Outside of the main poppet and the inside of the
unload valve must be free from scratch or damage.
3. Spring (3) must be free from fracture, deformation
or wear.
4. The main poppet and pilot seat(1) holes must be
free from foreign matters.
5. O-rings and back-up rings must be replaced with
new ones.
If allowable scratch is identified, remove it by
lapping.
If any part is found to be defective, replace with a
new relief valve assembly.
Assembling
1. Mount O-ring and back-up ring on the pilot seat(1)
and adjust kit(5).
2. Insert poppet(2) and spring(3) into the plug(4),
and temporarily assemble the adjust kit(5)
mounted with O-ring.
3. Insert into the inlet housing and adjust the
pressure.
Assembling work of main poppet shall be in
compliance with the paragraph 5.3.
Note:Ｏ-rings and back-up rings must be replaced
with new rings, not reused.
Pressure Adjustment
1. Install an accurate pressure gauge at the circuit
inlet
2. Operate the pump at the rated rpm
3. Replace the spool of the control valve, read the
pressure gauge at the end of the cylinder stroke.
4. Turn the adjuster clockwise until desired pressure
is reached.
Each turn of adjuster will raise 17.7MPa of
pressure （reference value）
5. At the specified pressure, hold the adjuster and
tighten with lock nut. Specified torque: 27～31Ｎ
・ｍ
6. Raise the pressure again to check if the specified
pressure is obtained
Note: When the main and second relief valves are
operated simultaneously, the setting pressure of the
main relief valve takes the precedence.
Installation
Take following cares at installation
・Pipe line must not exert unnecessary force to
valve.
・Mounting bolts must be tightened with same
torque.
・Welding work near valve may damage the seals
by excessive heat or scatter.
・Do not uncover valve ports until piping connection
to prevent dust from coming in.
Operation
・Valve arrangement must be in correct order.
Check that the hydraulic oil is clean, raise
pressure slowly(inching operation at low idle),
confirm that there is no external oil leak.
・Use hydraulic oil of which the annealing point is
82～113.
・Do not raise the pressure in the relief valve higher
than the specified setting pressure
・Make sure to provide sufficient warming up of the
machine before operation.
Especially, when starting up while the temperatures
of the hydraulic oil and valve is cold, take following
cares to prevent sticking of the spool by thermal
shock.
・Do not operate the main and second relief valves
successively during the warming up operation.
Circulate the hydraulic oil in the actuators to raise
temperature of all the parts evenly.
・Inching operation or composite operation may
cause local heating, therefore, must not be carried
out while the system is cold.
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