From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: [LML] Possible Gear Hydraulic System Vapor Lock
To: lml
Date: Thu, 11 Mar 2004 18:21:57 -0500
Message-ID: <web-3074771@logan.com>
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Posted for "Dave Saylor" <Dave@AirCraftersLLC.com>:

We've experienced this symptom too.  It seems to occur when there is an
internal leak that allows the high pressure side to slowly leak across to
the low pressure side, activating the low pressure switch, and making the
system think the gear is already down.  Then when you select "down", nothing
happens.  Normally the low pressure switch shuts off the pump after pressure
builds against the down and locked gear, but in this case the low pressure
switch is already seeing pressure from the leak.  As far as I can tell, the
leak can happen across the dump valve or across a leaky cylinder.  Lancair
has had a heavy duty dump valve for the 360 available for some time.

The problem is hard to duplicate in the hangar because if the leak is small
enough, it takes some time for the low pressure side to pressurize.  I've
been told that it may take a little normal, in-flight vibration as well.

Good Luck,

Dave Saylor
AirCrafters LLC
831-722-9141

  > > >   Flying with the gear up after a long and then short flight there was
no reaction to the gear switch being moved to the down position.  As
soon as pressure was released through the dump value the pump became
active.  I have replaced both the low pressure switch and the associated
gear relay with no change. < < <