Lorn,

If you have pressure in both high and low circuits then both tappet valves within the pump are closed at the same time.  When the pump is powered, the spool valve pushes one of the valves off its seat to allow return flow from the opposing circuit.  For some reason your spool valve is not holding the poppet valve open after the pump shuts down.  Does your spool valve have an O-ring?  It is the friction of this O-ring that keeps the spool valve from moving on its own.  It is actually rather stiff.  There does exist a spool valve for our model pumps without an O-ring.  The long term fix would be to figure out why some systems are locking up on both sides while others do not.  The first thing I would check is friction in the spool valve. 

A potential short term fix would be a momentary bypass on the pressure switches.  Having pressure on both sides at the same time is not a good situation.  While parked on the ground, the high side circuit should be vented.  Similarly, when in flight the low side is vented.  This prevents build up of pressure on the non-utilized side of the system.  These operating characteristics are shown in a series of video clips on the following page. 

 

http://www.n91cz.com/Hydraulics/Lancair_Hydraulics.htm

 

I hope you are able to get rid your your system's gremlins once and for all.  I know they have caused you much grief over the years.

 

Chris Zavatson

N91CZ

L360std

www.N91CZ.com