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I don't know if all the pumps
are the same internally through the years. I did have an older one with the
metal reservoir and now I have a new one with the plastic reservoir. They both
did the some thing in warmer temps.
These pumps were not made
for aircraft, they are marine pumps, used for lifting in/out drives on boats.
They work great in our planes and create plenty of pressure to do the job but a
boat hydraulic system is not set up the same as our little airplanes. The in/out
drive system doesn't use or require any pressure sensing switches. The pump
either pushes the drive up or down depending on the direction of the fluid flow.
When it gets to the end it just opens the preset pressure release valves inside
the pump and flows the fluid back into the reservoir. Our system needs the
pressure sensing switches so the landing gear will stay pressurized
either up or down.
So, the shuttle valve ( Spool
Valve ) in these pumps have no need to allow a path for the fluid to return to
the reservoir, unless it is running. The pump can be opened and modified to stop
the valve from closing so easily but I don't know what other effect this might
have on the functions of the pump to hold the pressures. Might be better to
externally solve this problem.
A T-shuttle valve can be had
from ebay or Lancair parts. They sell them for about $20 and I bought some on
ebay for $4.
It's all about
experimental...........
Randy
Stuart
LNC-2
----- Original Message -----
Sent: Saturday, February 09, 2008 3:43
PM
Subject: [LML] Re: 235/320/360 gear dump
valve idea
<<From:
Randy <randystuart
Then the pump pressurizes the high side and it
stops, and the shuttle valve centers,...>>
This
is where pumps in the fleet differ. In my two pumps the shuttle valve
does not return to center. It stays where the fluid last pushed
it. The O-ring on the spool offers up much more friction than the spring
on the poppet valve could ever hope to overcome. I am curious if all
pump vintages have O-rings on the spool valve and/or how snug the fit might
be? If the spool can be made to stay put, the problem goes
away. I am simply suggesting this as something to investigate before
a lot of new plumbing is added to the system.
A
little over a year ago, when this issue was last discussed, I took a series of
photos showing the effect of heating and cooling. What is observed is
that the high side pressure goes up and down with temperature (heat gun and
ice bath) while the low side remains at zero.
My
pumps are '95 and newer.
Chris
Zavatson
N91CZ
360std
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