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Posted for "Christopher Zavatson" <Christopher.Zavatson@udlp.com>:
George, Robert,
I have experienced the same thing twice in my 750 hours. I also heard
about the theory of a slow leak from the high to low side while
in-flight, thus pressurizing the low side enough to trip the switch. At
first this sounds quite reasonable, but I have been puzzling over two
questions. First, if enough pressure bleeds of the high side to bring
the low side up to 500 psi why didn't the high side have to cycle at
least once some time during the flight. (Which it didn't in my case) The second question deals with the inner workings of the pump itself. While the up side is pressurized, the spool valve opens a back pressure
circuit to dump the extra rod volume as the cylinders retract. With
this circuit engaged the max pressure achievable in the low pressure
side is 150 psi, the setting of the back pressure relief valve.
I did not have pressure gauges installed at the time. They would have
come in handy for diagnosing this event. I did, however, have momentary
by-pass switches for both high and low pressure circuits. A quick push
of the button sent the pump off and running. If it ever happens again,
I will glance at the gauges before doing anything.
Chris Zavatson
N91CZ
L360 std
This event as described has happened to me many times over the
eight years and almost 900 hrs. with my airplane. I attribute it to a very
slight leakage through the gear dump valve from the gear up pressure to the
down side, and just enough to push open the gear down pressure switch. <<<
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