lml@lancaironline.net Mailing List Archive

Chris,

Your guess as to the intermittent operation is correct. "AA" style pumps do not have a back pressure relief circuit. Unfortunately they cannot be turned into LB either.

To get the "AA" pump to retract smoothly you will need to run the high pressure side at a much higher pressure: High Side Operating Pressure + Low Side Relief Valve setting. ~ 1,200 + 900 = 2,100 psi. Definitely not ideal and thus the switch to the LB circuit.

As you recorded, you will see a much higher current than with the LB circuit since your pump is doing much more work throughout the entire retraction cycle.

Once you have pressure gauges installed, you will see the LPRV (Low pressure relief valve) setting on the low side gauge while retracting.

These settings are checked by forcing the pump on and letting it run up against the PRV. The pressure reading will remain constant once reaching the PRV setting.

Chris Zavatson

N91CZ

360std

http://www.n91cz.net/

From: Christopher Skelt <cskelt@earthlink.net>
To: lml@lancaironline.net
Sent: Tuesday, January 1, 2013 11:30 AM
Subject: [LML] LNC2 Hydraulics -- very old pump

Folks,

I finally tested gear retraction on my 1990 320 FB. Here's a symptom that may or may not be normal.

Gear Switch in down position. Master Switch off. Dump valve open.
Close the dump valve.
Master switch on. Pump runs for a few seconds, pressuring the low pressure side.
Gear switch to up position. Pump runs intermittently, raising the gear in fits and starts. Eventually gear is up and doors are closed. Pump stops and remains off—so no evidence of pressure loss.
Master switch off. Leave gear switch in up position. Gear stays up.
Open dump valve and gear comes down smoothly and locks.
Close dump valve.
Master switch on, and gear comes up continuously and steadily.
Gear switch to down, and gear comes down steadily.

I’m guessing the intermittent operation in 4 results from the pump competing with back pressure from the low pressure side.

The pump is identified as 108AA19-AL-3VT with a date stamp 10/89. It’s the old model with a cylindrical black metal reservoir. bought the kit in June 1990. Compare with 108AM19-CLB-3VT cited by Chris Zavatzson at http://www.n91cz.com/Hydraulics/Lancair%20Hydraulics.pdf

Is intermittent retraction normal without the benefit of the alternator charging for this variant of pump? Do we know if it is LL, LB, LD, or some other?

The battery is a fully charged Odyssey PC680. The voltage with the pump operating smoothly (see 8 and 9 above) is 11.3 Volts at 41 Amps retracting and 31 Amps lowering.

I have ordered pressure gauges for the high and low circuits. What pressure should I look for on the low side while retracting? How much is too much?

Thanks in advance for ideas.

Regards, Chris.