Posted for Sky2high@aol.com:

 
 Matt, et al,
 
 I am out-of-town and unable to send you some reference material - wiring
 diagram, hydraulic connection diagram and pumps parts layout for a standard
 Lancair hookup.  If I assume a standard hookup, I would have guessed from
 your
 picture that the pressure indicator was hooked to a tee (in place of  an ell)
on
 the lo side of the dump valve.  There is no mystery if the dump  valve is
 standard, it merely connects the hi (up) side to the lo (down) side of  the
 hydraulics so the fluid does not have to flow thru the pump - just between
 the
 opposite sides of the pistons in the actuators.  On jacks there is no
 condition
 I can think of that would prevent this flow since the nose gear and  gear
 doors are pushed out by springs and gravity.
 
 So, how can pressure be retained in both sides of the system with the dump
 valve closed?  assume some momentary back pressure can be built on the hi
 side
 when the gear is lowered and that it is retained - then, how can the
 pressure be increased by warm temps since hydraulic fluid should not expand
from
 temps (do you use mil spec fluid?)?  Even if it does, shouldn't everything
 else
 expand also (cyls, lines, etc)?  Also, there are pressure relief  valves in
 the pump that were supposedly set about 400 psi above the "stopping"
 pressure
 switches.
 
 The pressure relief valves can be adjusted per the diagram I will send to
 you. Some adjustment could result in the relief valve releasing enough
pressure
 so the hi pressure switch dead band is such that it will allow the pump to
 operate.  Of course, you will have to remove the pump and the reservoir to
 get
 access to these valves.  One must assume the crossover pressure occurs
 because there is leakage across or slight momentary misplacement of the
shuttle
 valve.
 
 Back to the dump valve - usually a ball valve rotating in a nylon chamber
 and designed for 600 psi as supplied by Lancair in early kits (maybe all
 kits).
 How then does the valve not "open" when opened?  Does the  nylon chamber
 rotate at high pressure and block flow?  Does the ball not  rotate at hi
 pressure?  A new valve?  Is there some crazy check valve  in the system?
 
 Perhaps the up pressure sw should be set for a slightly higher pressure
 (with the lo set as you have adjusted it) so it is not as sensitive to the
back
 pressure built during extension?
 
 BTW, I have similar conditions as mentioned by Mark - upon retraction one or
 more blips over a few seconds while everything is tucked away.  There  are
 more blips in warm weather than in cold weather.
 
 Scott Krueger  AKA Grayhawk
 LNC2 N92EX IO 320 SB  89/96