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Hydraulic Pump Troubleshooting
If the system fails to maintain clamping pressure, and no
oil is leaking from the cylinder, the failure may be caused
by foreign material or dirt in the hydraulic pump (there are
often aluminum ecks in the hydraulic oil from the pump
casting� These are normally of little consequence in pump
malfunctions)�
To diagnose problems in the pump, remove the internal
pump cover then reduce the level of hydraulic oil� Place a
piece of clear plexiglas completely over the reservoir open-
ing and screw it in place� Pump up the clamping pressure
and observe where the oil is returning to the reservoir�
Here are four possibilities to look for when diagnosing
hydraulic pump problems:
• Observe the holes on either side of the base of the
center post� If the oil is returning here, there is a bypass
problem� DO NOT attempt to adjust or repair the pump
in the eld. Return it to Gilson for repair or replacement.
• View the pump from above and at the plunger end to
see the intake hole (located on a raised shelf on the
bottom left side of the reservoir)� Oil is taken in here
when the pump plunger is pulled outward from the
pump casting� If oil leaks from this intake hole when the
pump plunger moves back into the pump casting, then
the intake check ball is not seating properly� Remove
the intake check ball� Clean it and its seat in the pump
casting� Check the ball for nicks or other damage, and
replace it if necessary�
• If the pump handle creeps back toward the pump cast-
ing after oil has been pumped into the cylinders, oil is
probably leaking back into the pump through the pres-
sure check thrust pin and O-ring assembly� Dirt or other
foreign material can prevent the O-ring from seating
properly� Remove and clean the thrust pin, O-ring, and
cavity in the pump to remove foreign matter� Also check
the O-ring for nicks or other damage, and replace the
O-ring if necessary. If the pump handle actually ies
toward the pump casting, then O-ring is usually torn,
and the assembly should be replaced�
• The pressure release hole is in the bottom of the well,
directly behind the center post� Oil normally returns to
the reservoir through this hole when the handle is pulled
all the way back to release clamping pressure� If oil
returns through this hole during pump-up, the problem
is with the pressure release pin or the pressure release
thrust pin and O-ring�If the Plunger O-rings have been
allowed to wear excessively, the hard steel plunger may
have scored the cast aluminum plunger bore� This wear
condition can not be repaired, and the pump must be
replaced�
To remove the plunger and replace O-rings:
• Remove the pump handle retainer pin and the two
plunger guide screws�
• Pull and remove the plunger and O-ring assembly�
• Replace the O-rings� Dip the O-ring end of the plunger in
hydraulic oil and reinsert it into pump body�
Reassemble the Testing Screen in the reverse order of
disassembly� Reinstall all covers� DO NOT plug in or try to
operate the Testing Screen without all covers installed�
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