Hyundai 35DS-7 Operation Manual page 166

2) HYDRAULIC GEAR PUMP
Problem
Pump does not develop full
pressure.
Pump will not pump oil.
Noisy pump caused by
cavitation.
Oil heating.
Foaming oil.
Shaft seal leakage.
3) MAIN RELIEF VALVE
P P roblem
Can't get pressure
Erratic pressure
Pressure setting not correct
Leaks
A good pressure gauge must be installed in the line which is in communication with the main relief. A
load must be applied in a manner to reach the set pressure of the main relief unit.
Then, follow these steps:
Loosen lock nut.
Set adjusting nut to desired pressure setting.
If desired pressure setting cannot be achieved, add or remove shims as required.
Tighten lock nut.
Retest in similar manner as above.
C C ause
System relief valve set too low or
leaking.
Oil viscosity too low.
Pump is worn out.
Reservoir low or empty.
Suction strainer clogged.
Oil too thick.
Oil filter plugged.
Suction line plugged or too small.
Oil supply low.
Contaminated oil.
Setting of relief valve too high or too
low.
Oil viscosity too low.
Low oil level.
Air leaking into suction line.
Wrong kind of oil.
Worn shaft seal.
Worn shaft in seal area.
C C ause
Poppet D, E or K stuck open or
contamination under seat.
Pilot poppet seat damaged.
Poppet C sticking in D.
Normal wear. Lock nut & adjust
screw loose.
Damaged seats.
Worn O-rings.
Parts sticking due to contamination.
6-22
Remedy
Check system relief valve for proper
setting.
Change to proper viscosity oil.
Repair or replace pump.
Fill reservoir to proper level.
Clean suction strainer.
Change to proper viscosity.
Clean filters.
Clean line and check for proper size.
Fill reservoir to proper level.
Drain reservoir and refill with clean oil.
Set to correct pressure.
Drain reservoir and fill with proper
viscosity.
Fill reservoir to proper level.
Tighten fittings, check condition of
line.
Drain reservoir, fill with non-foaming
oil.
Replace shaft seal.
Replace drive shaft and seal.
Remedy
Check for foreign matter between
poppets D, E or K and their mating
parts. Parts must slide freely.
Replace the relief valve.
Clean and remove surface
marks for free movement.
See How to set pressure on work
main relief.
Replace the relief valve.
Install seal and spring kit.
Disassemble and clean.