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Date: Wed, 13 Sep 2006 09:21:09 -0400
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From: "Mark Ravinski" <mjrav@comcast.net>
References: <list-1400024@logan.com>
Subject: Re:  Hyd Spool Valve Reverse Revisited
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Hi Larry,
I think your problem may not be with the plane.  At one time, you wrote a
dissertation of the gear system that was so good I actually made a copy of
it.
Of course, I can't find that now but that's beside the point.

Opening the dump valve connects the high and low side together but not to
the reservoir.  I expect you want the system this way as it is an additional
safety downlock of the gear.  Say for any reason you loose hydraulic
downpressure (pump failure, electric failure, internal leak, etc) then go
taxi around.  Would you be comfortable with just the overcenter locks on the
links to keep the gear from folding up.  Not me baby.

You could search the archives for "Henney, Spool Valve"  or just run the
test both ways - one of them is bound to work.

Cracking a fitting would not prove an internal cylinder leak - only that the
dump valve was open.

"Fastest LNC2 huh",  enjoy it while it lasts.

Mark Ravinski
N360KB 1390 hrs


----- Original Message ----- 
From: <lhenney@charter.net>
To: "Lancair Mailing List" <lml@lancaironline.net>
Sent: Tuesday, September 12, 2006 6:56 PM
Subject: [LML] LNC2 Hyd Spool Valve Reverse Revisited


> Scott, Chris, Lorn, all,
>
> I was reassembling a friends 360 Gear the other day and ran across a hyd
quirk that I've long forgotten.  The initial indicator was a classic
internal cylinder leak but it raised the "reversed spool valve" question to
which I am seeking an answer.  The plane is a no hydraulic pressure
indicator airplane making the trouble shooting more fun.
>
> Specifically, when the gear were down (a/c on jacks) and pressurized all
worked fine.  Then to do a fit check on the gear in the wells, we opened the
dump valve (all power off).  The back side hydraulic pressure was very
great.  The gear could not be raised by hand even with the dump valve open.
We cracked a hyd fitting to relieve the pressure (which worked).  This
indicates we have a internal cylinder leak.
>
> Additionally, it makes me ask if this would be correct spool valve
operation?  Specifically, my recollection was that a correctly installed
spool valve will bleed off the back side hydraulic pressure.  However, is
this only true in one direction?  That is, when the gear are up, does it
bleed the downside pressure?  Thus, the opposite would not be true and this
aircraft spool valve would be working correctly.  Do I have a problem (in
addition to the internal leak)?
>
> I've reversed 3 spool valves (not this one) and have forgotten which way
to run the test.  Do I put the gear in transit down, then reverse to up? Or
was it, run the gear up and then reverse to down?  Noting the nature of the
reversal (instantaneous or not).
>
> I would appreciate your clarity.
>
> Larry Henney
> N360LH
> "Fastest LNC2 in the Northern Hemisphere" again.......heh, heh, heh  :~)
>
> --
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>