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Anyone run into this problem ??
My
hydraulic pump has started to run continuously at 900 PSI instead of
shutting off at 1100 PSI
Bill,
Two
possibilities: You have an internal leak in the hydraulic system--fluid is
passing from the high pressure side to the low side, OR--you have an
internal pump failure.
The
pump failure is the least likely if it's been working normally, but if you can
get to your manifold easily, it may be the easiest/quickest to test? Simply
disconnect and plug the manifold outputs to the gear and flap control valves
(two lines). You'll need to keep the pressure sensor switch connected, and
the reservoir doesn't matter. Power the system up and see if it pressurizes
and shuts off (should do this almost immediately). If the pump continues to run,
pull it and check the internal bypass built into the pump first. If
it's not leaking, probably time to send the pump for
repair/replacement.
If the
pump shuts down at 1000-1100 psi, the pump is OK. You'll need to CAREFULLY
bleed the pressure and reconnect either the gear or flap feed line. (There will
be lots of pressure in the system, and you can't bleed it "normally" by cycling
the flaps). For this reason, I'd connect and test the flap circuit for an
internal leak as the next step...
The
leak can be either in the flap or the gear circuit, and the easiest of
the culprits to check is the gear/flap actuator valve itself. If either are
in an "intermediate" position, they will bypass fluid and cause this problem. Be
sure both gear and flap levers are moving all the way to the designated
position. (Although I recommended you start with the pump test, I'd probably
check these possibilities first as the easiest thing to assess-even a very small
mis positioning is enough to bypass fluid at 1000 psi.)
Another possibility is a failure of the internal seals
in the valve body, but a failure within one of the actuators is more
likely. You can assess both as follows. Actuate the pump with the flap circuit
(only) reconnected to the manifold. If the pump shuts off normally with the flap
connection restored, you've isolated the problem to the gear system. If the pump
continues to run with the flap circuit connected to the manifold, disconnect and
plug the flap actuator input line, either at the valve body exit, or under the
rear seat. Test again. If the pump runs, the valve body is at fault--flap side.
If it doesn't, the flap actuator cylinder is at fault.
Based
on ease of access, and having passed the gear lever position verification above,
I'd probably start by disconnecting and plugging each of the gear actuator lines
in turn, but if you can get to it easily, plugging the gear actuator line where
it comes from the manifold (before it tees off to the nose gear) will verify
that you don't have an internal gear valve leak. In any case, if you haven't
found the problem by now, you're probably facing a gear actuator internal
leak; it's only a matter of isolating each and testing until you find the bad
one... If you get through all three and didn't isolate a bad one, go look for an
internal leak in the gear actuator body.
Bottom
line: Lots of work, but I've tried to organize the search in order of ease of
test and most likely. If you're not dumping your fluid overboard, the
system is either leaking internally, or the pump just can't get to the
required 1100 psi any more...
Good luck, and let me know what
you found--these are always "fun."
Bob
Pastusek
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