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From: "Rumburg, William" <william.rumburg@cdicorp.com>
To: 'dfs' <dfs@gateway.net>, Lancair List <lancair.list@olsusa.com>
Subject: RE: Hydro again
Date: Wed, 19 Jul 2000 07:05:19 -0400
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          <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>>
          <<  Lancair Builders' Mail List  >>
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>>
> I'm thoroughly stumped! While I seem to have found a procedure that
> eliminates my basic problem, it isn't totally acceptable since that's not
> the way the system should function. Any ideas out there? Should I try to
> bleed the system again? I thought I did it quite thoroughly, and it is
> messy
> to say the least, but I'm open to any suggestions at this point!
> 
> Dan Schaefer
> 
Dan -
You've entered the world of the "backpressure relief circuit"!!!
While I can't give you an explanation of what is happening inside your
hydraulic pump, the symptoms are those experienced by early builders before
incorporation of the backpressure relief circuit in the pump. 
Dick Alden (a retired hydraulics engineer at General Dynamics in Fort Worth)
outlined the following symptoms in a 1994 issue of the LNN, told the reason
why and designed a "backpressure relief circuit" for the Oildyne hydraulic
pump, which cures the problem. Oildyne then incorporated it into all pumps
after 1994. While my own pump appeared to function without a problem many
times on the jackstand during construction, I eventually noted the same
symptoms:
1. If the gear is powered down, subsequent powered retractions are anemic
and incomplete (this cannot be cured by increasing the high pressure switch
setting)
2. If the gear is dropped using the pressure relief (free-fall) valve, a
subsequent powered retraction is always strong and complete.
Dick designed the backpressure relief circuit to cure this and returned his
pump to Oildyne for modification. I returned mine in 1995 and paid $ 100.
for the modification.
 
Bill Rumburg
N403WR  (Sonic bOOm)



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