CHAPTER 7
HYDRAULIC PUMP/PTO ASSEMBLY
7-1 HYDRAULIC PUMP.
7-1.1 Recommended Test Procedure.
a. Be sure there is an adequate supply of oil for the pump, at least one gallon of oil for each gpm of pump
capacity.
b. If one section of a tandem pump is being tested, make sure that all other sections not being tested are
adequately supplied with oil. If any of the other sections run dry, or if plugs are left in ports, serious and
permanent damage will result.
c. The oil should be a good quality hydraulic oil rated at 150 SSU at 100F. , with the oil temperature held at
120F. plus or minus 5F. (Test procedures are described in detail in SAE handbooks; see Hydraulic Power
Pump Test Procedure, SAE J745c. )
d. The feed line must be of adequate size with no more than 5" mercury vacuum adjacent to the pump inlet. As a
rule, the feed line must provide a feed flow velocity not in excess of 8 feet per second.
e. Hot oil must not be fed into a cold pump. It may seize. Jogging may prevent seizure.
f. Operate the pump at least two minutes at zero pressure and at moderate speed (not over 1500 rpm).
g. If pump becomes hot to touch, it is binding and may seize. This doesn't happen very often, but if it does, pump
will have to be disassembled and rebuilt, with extra care taken to remove burrs and to assure freedom from
binding.
h. Gradually increase pressure on pump, intermittently, until the desired test pressure has been reached. This
should take about five minutes.
i. Delivery should run close to rated catalog performance figures which are averaged from testing several pumps.
Something like a 5% lower reading may be used as a rated minimum if new or relatively new parts have been
used. When rebuilding the pump with parts from the original pump, which, while worn, appear satisfactory for
re-use, a 10% or 15% lower reading may be permitted, depending on the performance expected from the
equipment. One's own experience will prove the best guide here.
j. Measure the output at normal operating speed and at zero pressure, then again at 1000 psi (or the operating
pressure of the equipment) and allow a volume decrease approximating the listing below. It is suggested
reference only which makes allowance for re-used parts.
7-1
