SECTION 29 - HYDROSTATIC TRANSMISSION
29-18
HYDROSTATIC PUMP HIGH-PRESSURE
TEST
The hydrostatic drive system has a high-pressure
relief valve for forward and reverse, two relief valves
per pump or side. The relief valves, 1, for both pumps
and for forward and reverse are the same and the
same setting, 238 bar (3500 PSI).
If one relief valve is in question, the valve can be
switched with a known good valve; if the problem
follows the switched valve, replace the suspect
valve. Switching forward and reverse relief valves on
the same pump should reverse the problem if a relief
valve is the problem. If the problem remains, the
problem is most likely internally in the pump or motor.
Refer to the pump case drain test for further testing
to locate the problem.
Relief Valve Test Procedure
1. Raise the boom and rest on the boom locks.
2. Put the Service/Run switch in the “SERVICE”
position.
3. Engage the parking brake.
4. Securely block the skid steer with all four wheels
off the ground.
CAUTION
Failure to securely support the skid steer could
result in movement of the loader during testing
causing serious injury or damage to the
equipment.
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1
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5. Raise the operator’s seat and latch in the raised
position.
6. Remove the step shield.
7. Install a tee fitting in the high-pressure loop being
tested as shown at 1, motor fitting and install a
340 bar (5000 PSI) pressure gauge.
IMPORTANT: Check the hydraulic oil level and add
if required to insure sufficient oil for the test.
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