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From: "Rumburg, William" <wrumburg@cdicorp.com>
To: "'Steven B. Janicki'" <sjanicki@us.oracle.com>, 
	lancair.list@olsusa.com
Subject: RE: HYDRAULIC PUMP
Date: Wed, 1 Dec 1999 08:22:56 -0500 
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>>
> >>
> Has anyone completed a retrofit to their LN320/360 Hydraulic pump to the
> new
> style pump that has the large capacity reservoir? My hydraulic pump has
> started leaking between the motor body and the reservoir and am in the
> process of changing the leaking gasket and o-ring. As the older style
> hydraulic pump is no longer produced or available from Oilomatic or
> Lancair
> I am contemplating a retrofit to the newer pump in the future.
> 
	   Steve's question brings to mind another problem regarding Oildyne
hydraulic pumps that builders of pre-1995 320 kits need to be aware of. This
was reported in the LNN in 1994...
	Several years ago, Dick Alden, a retired hydraulics engineer in Ft.
Worth, discovered the following symptoms during gear retraction tests:
	1.) When the system was first cycled after a long idle, the initial
retract was normal with no problem; however, subsequent retracts were weak
and incomplete.
	2.) A powered retract following a free-fall (pressure release) was
always a good, strong retract (as it turned out, this was because of
pressure equalization within the pump internals).
	   Upon examining the gear pump design, he realized these symptoms
were due to the absence of a "backpressure relief" circuit within the pump.
He consulted with Oildyne and such a circuit was designed. He subsequently
returned his pump to Oildyne, who modified it to incorporate a backpressure
relief circuit (at no cost). My 1989 pump the same symptoms and I returned
it to Oildyne for the same modification just prior to my test flight in 1997
(at a cost of $ 100.). 
	   I haven't asked Lancair or Oildyne, but I'm sure that this
modification was thereafter incorporated in the design for all new pumps,
probably during 1995.
	  
	Bill Rumburg
	N403WR  (Sonic bOOm)
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