Wouldn’t you want to look at the pressure switches? If the pump
pressure never exceeds 950 pounds, the pump should never quit running.
No? Or can the switch shut off the power to the pump at 950 pounds? If
the pump quits prior to ±1200 pounds, something is afoul in the
switches or the pump thermally shutdown.
 Jim

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FROM: Lancair Mailing List [mailto:lml@lancaironline.net] ON BEHALF OF
Danny
 SENT: Thursday, March 29, 2012 8:03 AM
 TO: lml@lancaironline.net
 SUBJECT: [LML] Re: LNC2 gear diagnosis

Nope, I took the NW actuator out of the system and installed a gauge
on that pressure line to check.  I also played with the dump valve
today to see if a slight movement of the handle made a difference …
it did.  This weekend I’ll cap it and see what kind of pressure I
get but my guess is that’s the problem.

Danny

LNC2-360, 550 hours

N 38° 43' 25.7"

W 77° 30' 38.6"

FROM: Sky2high@aol.com [mailto:Sky2high@aol.com]
 SENT: Wednesday, March 28, 2012 9:06 AM
 TO: lml@lancaironline.net
 SUBJECT: [LML] Re: LNC2 gear diagnosis

Danny,

From what you reported it would seem that the nose gear actuator is
the real problem. How about the door actuators? One possible analysis
is that you don't see the 1200 psi because the leak is greater at the
higher pressure and then slows a bit as the pressure goes down or the
actuator has its worse leak at full retraction and less when the
piston is not at the full retraction position...

Scott Krueger

In a message dated 3/27/2012 10:32:25 P.M. Central Daylight Time,
danny@n107sd.com [1] writes:

If any of you have a suggestion, I’d appreciate your input.

On my last flight home, with no early signs of failure, my gear pump
was tripping on about every 2 seconds to maintain pressure.  I
figured I had a leaky actuator and would have to rebuild it to
resolve this; no big deal.  I found one leaking and figured where
there is one, there may be more.  So, I’m rebuilding all of
them.  But, before doing so, I put a gauge on the high pressure
side of the pump to see if I had internal leaks there too.  What I
found was that my pump will only pressurize to about 950 psi (should
be ~1200 psi) and then it bleeds down slowly.  I tried to adjust
the pressure switch but it made very little difference.  To verify
the bleeding, I isolated all actuators out of the system except the
nose wheel.  I put the gauge on the high pressure side of the NW
actuator line, selected gear up to pressurize the system, and then
quickly crawled under the plane to look at the gauge.  It was
bleeding down so fast that by the time I got down there to look at
it (~2 sec.), it had already lost about 200 psi and then bled down
the rest of the way in about 7 more seconds.  So, and here’s the
question, do I have a faulty gear dump valve, a leaky pump, or both?


Danny

LNC2-360, ~550 hours

N 38° 43' 25.7"

W 77° 30' 38.6"

Links:
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[1] mailto:danny@n107sd.com