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The problem is caused by the hudraulic pump not
operating as desired. The shuttle valve inside it comes off its end stop and
traps fluid in the lines. This trapped fluid expands with temperature increase
increasing pressure in the lines and trips the pressure switches. Since the
switches are now open, no electricity can get to the pump morot . . . gear
failure.
There are three solutions to this
problem.
1) add an accumulator to the hydraulic
system.
2) rebuild and possibly modify the the pump
3) install my electric module that monitors the
pressure switches and automatically runs the pump to vent the offending
pressures.
Wolfgang
----- Original Message -----
Sent: Wednesday, April 16, 2014 10:06
AM
Subject: Gear Down...INOP
I believe that I recently experienced something in my Legacy that
I remember reading about but can't remember all the details. I looked
into the LML archives and was unsuccessful. Could someone out there
please briefly summarize the situation, reason and any possible remedies for
gear extension failure following high altitude cruise in cold air followed by
a decent and landing in hot air. I seem to remember a discussion about
boosted pressure in the hydraulics plumbing due to the rapid rise in
temperature which in turn had an effect on the operation of the pressure
switch In my recent experience...after opening the dump valve, the
hydraulic pump did run, confirming continuity to the pump. After working
the nose gear into the locked position, the landing was uneventful but I would
like to avoid this uncomfortable situation in the future. Would a tweak
on the pressure switch adjustment be called for here or just expect to
momentarily crack open the dump valve to relieve excess pressure. Thanks
for your thoughts.
William Ford
N11LL
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