Sender: <marv@lancaironline.net> (Marvin Kaye)
To: lml@lancaironline.net
Date: Fri, 12 Mar 2004 14:46:09 -0500
Message-ID: <redirect-3076243@logan.com>
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From: "Lorn H. Olsen" <lorn@dynacomm.ws>
Subject: Re: Possible Gear Hydraulic System Vapor Lock

Hollis & Christopher,

I sent my whole pump (1998 vintage) back to the factory to have them 
rebuild it and calibrate my new pressure switches. I wanted both 
pressure switches and both relieve valves calibrated. They told me that 
the spool valve had been in backwards and they fixed it.

I then installed pressure gauges from Lancair under the passenger seat 
so that I could tell what was going on with the gear. I tested my gear 
on the ground and it stayed in the up position with no loss of pressure 
for over 15 hours. The high side had 1,200 lbs of pressure, the low 
side had 0.

When my gear is up and I fly at high altitudes, every hour I can hear 
the pump run for 1 second while it re-pressurizes the high side. That 
means that I have lost 300 lbs in the high side. I know that the 300 
lbs is going to the low side because I can see it with my pressure 
gauges. There is no atmospheric venting.

After 2 hours of flying, the high side will have 1,200 lbs and the low 
side will now have 600 lbs of pressure. When I put the gear in the down 
position, nothing will happen because the low side only comes on when 
the pressure is below 400 lbs. The low side runs from 400 to 700 lbs of 
pressure and the high side runs from 900 to 1,200 lbs (it may be 700 to 
1,000 lbs, I forget). I have to open my dump valve to relieve some of 
the pressure.

Now for the real cause of the problem. I believe that the rubber O 
rings that we use in our activators contract enough at cold 
temperatures that there is a leak from the high side of the activators 
to the low side. I fly a lot at 15,000 feet and it is a lot colder up 
there. My high flights are where I have noticed the problem. I don't 
think that I have the problem at low altitudes.

Any further suggestions and/or observations are welcome.

Sincerely,
Lorn

> From: "Christopher Zavatson" <Christopher.Zavatson@udlp.com>
>
> Dave,
> <<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,>>
> When the spool valve is installed correctly the down circuit is 
> essentially open to atmospheric pressure via the reservoir.
> .
> .
--
Lorn H. 'Feathers' Olsen, MAA, DynaComm, Corp.
248-478-4300, mailto:lorn@dynacomm.ws
LNC2, O-320-D1F, N31161, Y47, SE Michigan