<<Consider that if the
spool/shuttle valve is stuck in some bad spot and the pressure is equally very
high on both sides so that the dump valve cannot release the pressure,
there may exist problems with the relief valves. Besides that,
some of us have symmetric spool valves and some of us have offset ones.
It is hard to install the symmetric ones backwards.
Peculiar pressure build ups associated with heat expansion may also be
associated with the pump relief valves. Mike Reinath claims that his
relief valves operate differently when the pump runs. He has adjusted
his to be close to the pressure valve action.
The pump manufacturer claims that the relief valves should be set about
400 psi higher than the circuit requirement. Theoretically, the
manufacturer has set the relief valves for about 1000 (600 lo pressure)
and 1500 (1100 hi pressure). Also remember that pressure switches have a
dead band - I.E. it may be triggered (to open) at the high side of its
pressure setting and the pump may continue to run long enough to raise the
pressure even more. Then, the pressure switch may not close
again until the pressure has dropped several hundred psi below its
setting. Or, maybe not. Hydraulic logic is not precise in this
application.
In my case, gear up operation frequently pauses before another blip
finally tucks away everything nice and tight. Why? Because a spike
opens the pressure switch prematurely and a few seconds later,
pressure has degraded enough to re-activate the switch. A leak, you
say? No, because that ultimately sucked up gear will remain up
tight for days whilst the plane is on jacks. 'Splain that Lucy?
Or, is it because that wild and crazy nose gear gas spring behaves
differently at the end of a fast retract, then relaxes a
bit after it is compressed for a few seconds and that causes a slight
drop in the "hold it all up" pressure? Is it my Karma?
Perhaps you should set your gear down pressure switch to a bit higher
pressure. Perhaps you should install a pressure switch bypass switch as
some have done. I dunno. The current dump valve resolution doesn't
seem too bad when the occasional problem occurs.>>