lml@lancaironline.net Mailing List Archive

Several folks have been asking privately about the spool centering springs mentioned below. This link contains both schematics and photos showing how to revert a new pump back to the original 320/360 functionality.

http://www.n91cz.com/Hydraulics/Pump-Unlock.pdf

Chris Zavatson

N91CZ

360std

www.N91CZ.net

From: Chris Zavatson <chris_zavatson@yahoo.com>
To: lml@lancaironline.net
Sent: Wednesday, February 1, 2012 12:46 PM
Subject: [LML] Re: 320/360 Hydraulic Pressure Switch

Lorn,

Had the temperature been 90 or 100 degrees your pressure would have been even higher. In some of my hydraulics videos, you will see the 2,000 psi gauge pegged on occasion during thermal heating tests.

http://www.n91cz.com/Hydraulics/Lancair_Hydraulics.htm

Your predicament of having to crack a hydraulic line is exactly what can happen if the spool centers after pump shut down. I find that a completely unacceptable design. Imagine taking off into IMC and the gear won't come up. I had the opportunity to test out a pump in this configuration last summer. Just as you experienced, I was able to reproduce a complete lock up.

http://www.n91cz.com/Hydraulics/NewPumpLockUp_0001.wmv - hi res

http://www.n91cz.com/Hydraulics/NewPumpLockUp_0002.wmv - low res

After discussions with Lancair and Parker, I reverted the configuration back to the original 320/360 config and all is good now. Only one side can ever be pressurized at a time. Unfortunately due to employee turn-over, no one currently at Parker or Lancair knows why the centering springs were added. After reviewing the 320/360 system both agreed that a system lock up is possible using replacement pumps currently sold (108AMS32-CZZ-3V-14-08-Y). Parker sent me parts to revert three pumps back to the original configuration.

The TRVs in our pumps are the lowest available -fixed setting of 2,500 psi. This may be too high to protect some of our components. I have run them up to 2,000 psi. In flight, I have seen 1,800 psi, descending from 18k into the southwest deserts.

Chris Zavatson

N91CZ

360std

www.N91CZ.net

From: Lorn H Olsen <lorn@dynacomm.us>
To: lml@lancaironline.net
Sent: Wednesday, February 1, 2012 6:33 AM
Subject: [LML] Re: 320/360 Hydraulic Pressure Switch

Again,

My Oildyne internal pressure switch came (set by Oildyne) at 1,500 PSI. How do I know? I parked my plane on the ramp at Newport News, Va in the evening. The temperature was 40°F. 3 days later, when I was going to take off. The temperature was 80°F. I looked at my pressure gauges. Both the up and down were at 1,500 PSI. I had to crack a nut in a hydraulic line to release the pressure. The gear would not go up or down, at this pressure. The emergency dump valve would not release, at this pressure. The pump would not run at all, at this pressure.

Now, I have Wolfgang's high pressure adapter in the system. It runs the pump whenever the pressure is high on both the up and the down side.

There is no speculation here. Just the facts, mam.

--
Lorn H. 'Feathers' Olsen, MAA, ASMEL, ASES, Comm, Inst
DynaComm, Corp., 248-345-0500, mailto:lorn@dynacomm.us
LNC2, FB90/92, O-320-D1F, 1,800 hrs, N31161, Y47, SE Michigan

--
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