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Date: Sun, 10 May 2009 17:55:08 -0400
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From: John Cooper <snopercod@citcom.net>
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Subject: Re: LNC2 Nose gear door
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Yes, I had a similar problem, and it was because fluid was leaking past
the ball-check in the sequence valve. I replaced the valve and that
fixed the problem.

It almost has to be the sequence valve, because for the door to close,
hydraulic fluid must pass through the sequence valve to the door
cylinder. Either the valve is leaking though, or it is being actuated
before the gear is up. My guess is that your replacement valve is
leaking just like the old one did. All it takes is a little speck of
dirt to get stuck under the ball-check valve.

These sequence valves are basically just a check valve which block the
flow of fluid in one direction until the ball is mechanically pushed off
the seat by the plunger. There's a spring under the ball which normally
holds it against the seat.

There should be no pressure on either side of the door cylinder while
the gear is coming up until the nose strut actuates the sequence valve.
To find out, you could remove the hydraulic line from the door cylinder
and see if any fluid is leaking out with the sequence valve plunger
removed so it can't actuate when the gear is up. Either that, or hook up
a pressure gage.

May we assume that the sequence valve is installed in the correct direction?