REFLECTOR: Gear dump valve

[Al Gietzen]

I also wore my valve out during construction.  It started leaking internally


not long after first flight.  What I would do is raise the gear with the 

pump, then lower it slowly to certain positions so I could work on the gear.


This resulted in the valve leaking through which led to the pump running 

about every few seconds when on the ground.  I could open and close the 

valve and it would improve the situation but only temporarily.  So, be 

careful opening/cracking the valve with pressure on the system.

Ronnie 

 

I did the same cycling of the valve without affecting the valve.  The
pressure at the valve necessary to 'hold' the gear at an intermediate
position is relatively low; I don't remember what I measured, but IIRC, less
than 100 psig; which should not damage the valve.

 

One factor that could affect the valve is the very high pressure left in the
system at the end of the gear down stroke.  As verified with a pressure
gauge, the pressure spikes up to over 1,000 psig (to the internal bypass
pressure of the pump).  This results from the fraction of a second that the
pump continues after the pressure switch breaks the circuit.

 

Leaving this pressure in the system for long periods after lowering the gear
certainly stresses the ball seat in the valve, and, of course, the seals in
the cylinders.  I concluded that it is good practice to momentarily crack
open the dump valve after the gear is down and locked, and the master is
off, to relieve the pressure.  It is otherwise likely to eventually find its
own path to reduce pressure.

 

Of course I have no direct evidence that this is necessary or helpful, but
it makes sense to me.

 

Al

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