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B. On systems that fail to prime or lose their prime, check for the
following:
1. Correct unit mounting position in the case of a pump motor
combination. It is either horizontal or vertical and failure to
mount in proper manner could mean pump cannot prime (pick
up oil) because the suction tube is not submerged in the oil at
all times. Note: All pumps designed for vertical mounting have
a label stating such.
2. Partially clogged suction filter.
3. A loose or improperly installed suction hose or pick up tube.
4. A bad front pump seal.
5. A solid fill plug in reservoir with no vent.
6. Oil that is too thick (See Hydraulic Fluid Section), or
commercial with water.
7. Occasionally a pump will not prime itself because a check
valve spring in the high pressure port is too "stiff" or the spring
retainer is turned down too far. If this condition is expected,
loosen the spring retainer, (it is found in the 3/8 high pressure
outlet port), energize the pump to prime it, and then turn the
retainer back to the correct depth. (See Section on Check
Valves.)
12. Hydraulic Pump Electrical Problems
Warning: Remove all rings, watches, etc. prior
to doing any electrical work.
A. Low Voltage
Operating direct current (DC) power units efficiency requires
proper voltage. Any attempt to operate below the minimum
required voltage could cause system failure. Signals which
point to low voltages are:
1. Motor running at reduced speed.
2. Solenoid valves not shifting.
B. Minimum voltage readings are as follows:
1. The minimum voltage between the motor stud and ground is
9.0 volts at maximum load conditions.
2. The minimum voltage between the valve solenoid power
wire ("hot wire") and ground is 9.5 volts at maximum load
conditions.