REFLECTOR: Gear dump valve

[Terry Miles]

Me too.


-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Al Gietzen
Sent: Friday, March 03, 2006 6:47 PM
To: 'Velocity Aircraft Owners and Builders list'
Subject: REFLECTOR: Gear dump valve



 

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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