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Randy,
I don't doubt your observations. I am just really curious what is different in your pump. The only way I can see this happening is if the spool doesn't stay put after the pump shuts down (slide 21 from my previous post). If the spool goes back to center both high and low circuits become isolated. Once that happens, temperature rise or and internal leak can lock out the pump.
I've had my low side pressure go off the scale of the pressure gauge (1,200+ psi) while he plane got baked in my old hangar. The high side remained at zero. Similarly when descending into hot desert air from 18k, the high side has hit 2,000 psi. The low side remained at zero. When the spool remains in place, this makes perfect sense. The non-operating side has a low resistance escape path and cannot retain pressure. I would love throw your pump on the test bench. Let me know if you are interested
I just did a more comprehensive video of thermal cycling for the hydraulic system, retracted, extended, under heating and cooling. Time is sped up 2x to keep the total length reasonable. Worth noting is that the non-active side always remains at zero.
Chris
Chris Zavatson
N91CZ
360std
From: randy snarr <randylsnarr@yahoo.com>
To: lml@lancaironline.net
Sent: Sun, April 3, 2011 11:40:56 PM
Subject: [LML] Re: LNC2 Gear Hydraulics
Chris,
Both sides of my system rise and fall with temp...
This is why I installed a dump valve with an extra line that dumps to zero pounds on both sides when opened rather than just equalize and still be under pressure. I too used a wrench a few times to release the pressure. I believe this condition is a little worse in my plane as I replace the large factory supplied hose with small tight stainless braid lines that most likely resist expansion more than the big factory rubber hoses...
RS
"Flight by machines heavier than air is unpractical and insignificant, if not utterly impossible"
-Simon Newcomb, 1902
--- On Fri, 4/1/11, Chris Zavatson <chris_zavatson@yahoo.com> wrote:
From: Chris Zavatson <chris_zavatson@yahoo.com>
Subject: [LML] Re: LNC2 Gear Hydraulics
To: lml@lancaironline.net
Date: Friday, April 1, 2011, 8:34 AM
Keith,
You should never have to resort to wrenches to get the wheels up –and that is not just speaking from a safety perspective.
The following is an extract and renumbered set of slides from a LOBO maintenance seminar on the 320/360 hydraulic system. Slide 21 shows one possible explanation for your system’s failure to retract.
http://www.n91cz.com/misc/LancairHydraulics-LML.pdf
Temperature changes will cause pressure to go up and down, but should only affect the currently operating side of the system. The non-operating side should be zero and remain zero unless there is some other failure or configuration issue. If both operating and non-operating sides are affected by temperature – investigate.
Note that earlier vintage pumps (~235 era) were internally different.
You may also find some of the following of interest:
http://www.n91cz.com/Hydraulics/Lancair_Hydraulics.htm
Chris Zavatson
N91CZ
360std
www.N91CZ.net
From: Keith Smith <keith.smith@gmail.com>
To: lml@lancaironline.net
Sent: Thu, March 31, 2011 12:24:59 PM
Subject: [LML] Re: LNC2 Gear Hydraulics
Quite possibly one of the best posts I've ever read. Thanks, Tom, for taking the time so share those experiences!
I recently experienced the inability to raise the gear. A quick call to Rick Argente (Lancair owner/builder in NJ) provided the solution...bleed the line. He said it's a common issue when flying from cold locations (NJ) to warmer destinations (Georgia).
I also get hear the pump activate in flight for a fraction of a second every 20-30 minutes or so, which I suspect points to a leak of some sort.
Keith
Smith
N360JH
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