From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: [LML] Hydraulic issues... more info after tests
To: lml
Date: Fri, 07 Jul 2006 00:11:57 -0400
Message-ID: <web-1226986@logan.com>
In-Reply-To: <4b9.3925a35.31de6a0e@aol.com>
References: <4b9.3925a35.31de6a0e@aol.com>
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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