Message-ID: <000201bff113$195a8aa0$fe31143f@oemcomputer>
Reply-To: "dfs" <dfs@gateway.net>
Reply-To: lancair.list@olsusa.com
From: "dfs" <dfs@gateway.net>
To: "Lancair List" <lancair.list@olsusa.com>
Subject: Hydro again
Date: Tue, 18 Jul 2000 15:30:06 -0700
Mime-Version: 1.0

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Here’s a strange, as Paul Harvey would say.

A few weeks ago, I had posted my travails with my hydro system, where my
gear pump had started to “pulse” after retraction. By isolating each part of
the system, I ultimately traced the problem to the right main cylinder which
apparently was leaking internally. After rebuilding the cylinder, things
seemed OK when the gear was exercised on jacks, so I went flying. After an
initial pulse or two following retraction things settled down, it looked
like I had fixed the leak.

Several days later however, the problem was back as before. I figured that I
must have damaged the seals during rebuild but first decided to try bleeding
the system once again. I did, and then to test things, I ran the gear up and
down on the jacks – and this is where things started to get weird.

Raising the gear the first time, everything was normal – no pulsing. I put
the gear down with the pump (normal operation) and then raised it again. The
pulsing was back! For some reason, I decided to drop the gear with the
dump-valve and then raise it again. This time – no pulsing! Now I really had
a head-scratcher!

Next, I decided to try something really bizarre: with the gear up and the
pump pulsing (which I could make happen if I ran the gear down with the pump
and then raised it again) I momentarily flipped the dump valve open and then
re-closed it, probably for no more than half a second. The pulsing stopped
and did not start again – I left the plane on the jacks with the gear up for
an hour and it didn’t start again. Yet, if I ran the gear down via the pump
and then did a retract, the pulsing would always be there.

I flew for over two hours the last two days and by momentarily flipping the
dump valve right after full retraction, I had no pulsing problem whatever.

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


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