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John,
In 920 hours I've seen this particular hiccup only
once. It was exactly as described by Randy (hot day after landing on a
cool night). Although a "real" dump valve is a super fix, another get
home road alternative is to open the dump valve and short across the down
switch momentarily. This pump chirp bumps off the back side pressure (by
virtue of engaging the motor).
Some folks have little secret switches for bypassing
the pressure switches but I've only seen this problem once in 920 hours.
Alternatively, dumping the pressure and reclosing the valve upon shut down is
99% affective, too.
Larry Henney
N360LH
Spry Debongers (850 hours trouble
free!)
John,
This has gone around several times.
The dump
valve you have is really a pressure equalization valve.
A true dump
valve will dump the pressure to 0. I will explain.
This has
happened to me as well. I installed hydraulic gauges which tells the
story. When you pull the airplane out of a cool hangar into the warm sun,
the system heats up and pressure on both the high and low sides increase
pretty much equally. Example: my high pressure (gear up) side may start at
0 and the low side ( gear down) at 500 when in the cool hangar.Pull it
into the sun for 30 minutes and both will increase say 700 psi. No
kidding! That puts the high at 700 and the low at 1200. If the increase of
the system hits 900 or so ( low now at 1400 high at 900) you
have hit the gear up limit pressure switch which tells the system (if it
were in transit) to stop raising the gear. In your case, when you try to
retract the gear the upper limit just keeps the pump from starting as it
thinks the gear is already up because the upper limit has already been
hit. In our systems, both sides are closed meaning neither vents to the
resevoir when the pump is not running. This changes when the pump is
running. If you increase the pressure enough on both sides (again with
heat) while on the ground the the pressure on the high side will
eventually open the upper limit pressure switch. and the gear will not
retract. Sometimes opening the dump valve will help as it equalizes the
pressure on both sides. If this equalization results in the high side
dropping below the high side limit (appx. 900 psi), the gear will retract.
It the equalization does not result in this it will not, thus you have to
climb out and crack a fitting somewhere releasing the heat induced
pressure increase in the system.
This happened a few times for me and I
think I am more suseptable to it as I used small hot rod stainless braid
hydraulic lines instead of the factory rubber stuff. I think the factory
stuff although much heaver has some flexibity allowing it to balloon a
little limiting the heat induce pressure increase. I solved this by
replacing the dump valve that does more than connect the high and
low pressure sides. Mine does that but it has an extra line that not only
connects the high and low pressure sides equalizing pressure on each side,
it also dumps the pressure to 0 with a low pressure return line to the
resevoir. If you had my dump valve and low pressure return line, you would
have been able to retract the gear by cracking the dump valve and closing
it again as you would truely have dumped pressure not just equalized
pressure.
I have heard of some doing a bypass on the pressure switch to
momentarily get the gear pump to move, for me I like my set up which is
similar to the Legacy. I like the idea of being able to release all
pressure from the system, not only to solve the issue describe here but to
ensure I can always get
the wheels down without power as there is no way to keep the gear up if
you vent the pressure to 0.
FWIW...
Randy
Snarr
N694RS
235/320
--- On Tue, 4/6/10, John Spry
<spry@paradise.net.nz> wrote:
From:
John Spry <spry@paradise.net.nz>
Subject: [LML] gear retract
problems - 320
To: lml@lancaironline.net
Date: Tuesday, April 6,
2010, 5:59 AM
My 320 gear did not activate when I
selected gear up yesterday - I checked the circuit breaker, opened and
closed the dump valve, selected gear down, then up - all to no avail and
then landed.
I recalled some discussion years ago about
this issue and a temporary fix being the "cracking" of the hydraulic
pressure to get the system going again - this I did and it worked
!
Can someone help me with identifying the
actual cause and permanent fix.
Thanks
John Spry
L320 __________
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