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Bob Belshe and all.
The experience I have had with my 320 is exactly like
yours. On jacks, I have always made it a habit to push the gear up
into the well to check for fit and free fall. The dump valve is open for
this. After every flight and after engine shutdown, before I turn off the
master switch, I always open the dump valve and let the pump run for a couple
seconds then shut off the master, leaving the dump valve
open.
George Shattuck
N320GS, 1989 kit
Danville, CA before moving to Georgia.
Sent: Wednesday, November 22, 2006 12:55
AM
Subject: [LML] Re: Electrical /Hydraulic
system questionslancair235/320
:
The fluid circuit is really a closed loop. The only options for
returning fluid to the reservoir are either through one of the pressure
relief valves or the low resistance back pressure circuit. Excess
fluid needs to return to the tank every time the rod volume displaces
fluid volume. When the rod volume is removed from the system, make
up fluid is pulled in from the tank through a one way check valve.
During retraction, the spool valve opens a low resistance path from the
low side to the reservoir, eliminating a large pressure build up in the
low circuit during retraction. - which also eliminate the possibility of
pressure build up due to thermal influence.
One side effect of the correct spool valve orientation and a leak
free system is that you cannot manually push the gear up even with the
dump valve open unless the spool valve is moved into the retract
position. After opening the valve you still have a closed loop from
high to low that is now bypassing the pump. When you try to push the
gear up you get hydraulic lock. You are trying to add the rod volume
to a closed system and the only route back to the reservoir is
through a relief valve. By bumping the pump in the up direction,
even with the dump valve open, you can push the spool valve into the
retract position which opens up the low resistance path to the
reservoir for the low side circuit. If you are able to push the gear
up at all without bumping the pump, I would suspect the spool valve is
backwards. Let us know what observe in the low circuit during
retraction. You can also try the direction-reversal test during
retraction. The response should be instantaneous.
good luck
Chris,
It would seem that there is no one
answer for this problem.
On my 235, with the plane on
jacks;
I can open the dump valve and easily
push any of the gear up. Spool valve is
backward?
When I do the direction reversal test
the gear reverses instantly. Spool valve is OK?
When I put the gear up and then open the
dump valve, all 3 drop within 2-3 seconds.
Years ago, I experienced a few instances
of the gear not coming down when the gear switch was put down. This
situation was always relieved by briefly opening the dump valve. It
stopped happening, so I did not change anything.
Am I just lucky, or what?
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