lml@lancaironline.net Mailing List Archive

Chris, thanks for the feedback and the work you did.

I sense a contradiction in this statement;

[Our pumps come with the lowest of three fixed TRV values. The set-point is 2,500 psi, thus the statement "approximately 100-140 bar (1500-2000 psi) above the system relief valve pressure" still holds true.]

I see two interpretations.

1… The TRV “setpoint is 2,500 psi”, presumably referenced to reservoir pressure, which is ambient cabin pressure assuming the reservoir is well vented. Thus the TRV will limit the output pressure to 2,500 psig max. In that case the graphs in the brochure do not apply for our pumps above 2500 psi.

2… The TRV setpoint is “(1500-2000 psi) above the system relief valve pressure.” I interpret “system relief valve pressure” to be the setpoint of the internal HPRV or LPRV located upstream of the check valves. These set points are not specified in the brochure, but the performance graphs indicate that the HPRV is at least 3,000 psi which would make the TRV setpoint 4,500 - 5,000 psig.

Perhaps you are saying the TRV setpoint is 1,500 – 2,000 psi above the pressure switch setpoint’s, but I was commenting on this quote from the brochure which says something else.

“It is a fixed relief valve with a pressure setting approximately 100-140 bar (1500-2000 psi) above the system relief valve pressure.”

If the TRV setpoint is lower than the HPRV and LPRV setpoints I see no need for the HPRV and LPRV. What is their purpose?

I would like to know how much pressure it takes to keep the wheels in the wells during a high speed high G pullup. If the relief valve lifts and the gear comes out of the wells, it could literally blow the doors off the airplane. If anybody with gauges does a gear test in the next few months, please note the pressure just before the gear tightens up in the wells and let me know. Five times that number should be about right.

Regards,
Bill Hannahan
wfhannahan@yahoo.com

From: Chris Zavatson <chris_zavatson@yahoo.com>
To: lml@lancaironline.net
Sent: Wednesday, February 1, 2012 11:20 AM
Subject: [LML] Re: 320/360 Hydraulic Pressure Switch

Bill,

Our pumps come with the lowest of three fixed TRV values. The set-point is 2,500 psi, thus the statement "approximately 100-140 bar (1500-2000 psi) above the system relief valve pressure" still holds true.

re: question three:

3… Does the momentum of the motor cause the pressure to spike well above the pressure set point?

The pressure does shoot beyond the set point due to inertia of the motor and pump. As the hoses etc. stretch in the first second or two, the pressure comes back down a bit. The stiffer the system is, the greater the pressure will shoot beyond the set-point. On the test bench with a mere 3 feet of hose, the overshoot is quite a bit greater that in a fully populated aircraft.

Chris Zavatson

N91CZ

360std

www.N91CZ.net

From: Bill Hannahan <wfhannahan@yahoo.com>
To: lml@lancaironline.net
Sent: Tuesday, January 31, 2012 3:46 PM
Subject: [LML] 320/360 Hydraulic Pressure Switch

Regarding this quote on the trv from the Oildyne brocure;

“It is a fixed relief valve with a pressure

setting approximately 100-140 bar (1500-2000 psi)

above the system relief valve pressure.”

As I read this, if the pump is rated to produce flow at 3000 psi, the TRV is set for 4500 – 5000 psi. That seems way too high for our systems.

The third set of pressure switches on my 360 are acting up. I am thinking about a spring project to upgrade them. I bought two new/old stock pressure switches for about $75 including shipping.

http://www.ebay.com/itm/DIRECT-AUTOMATION-PSD25-0P-1450H-PRESSURE-SWITCH-/220904940181?_trksid=p3286.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D3%26po%3DLVI%26ps%3D63%26clkid%3D6005931030562248892

They are limited to 250 ma load current and a max overload of 2900 psi. My plan is to reset the TRV’s to the neighborhood of 1200 psi. At that pressure motor current is less than 30 amps.

I found 50 amp PNP Darlington transistors to replace the big power relays. They have enough gain to be driven directly from the pressure switch through an appropriate resistor.

http://www.ebay.com/itm/MJ11032-Darlington-Power-transistors-NPN-Audio-Amp-x2-/180663839378?pt=LH_DefaultDomain_0&hash=item2a10676a92

I would appreciate some information from those who have installed pressure gauges.

1… At what pressure does your up pressure switch close and open?

2… At what pressure does your down pressure switch close and open?

3… Does the momentum of the motor cause the pressure to spike well above the pressure setpoint?

4… In high G pull-ups and/or turbulence, do you see fluctuations in pressure, from what to what?

Thanks for your feedback.

Regards,

Bill Hannahan

wfhannahan@yahoo.com

--- On Mon, 1/30/12, Bruce <BGray@glasair.org> wrote:

From: Bruce <BGray@glasair.org>
Subject: [LML] Re: IV-P Hydraulic Pressure Switch
To: lml@lancaironline.net
Date: Monday, January 30, 2012, 12:05 PM

You might look at,

http://www.automationdirect.com/adc/Shopping/Catalog/Sensors_-z-_Encoders/Pressure_Sensors_-a-_Pressure_Gauges/Pressure_Switches/PSD25-0P-5800H

Solid state and adjustable, don’t forget the matching cable

Bruce
WWW.Glasair.org

-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of Craig Berland.
Sent: Monday, January 30, 2012 10:53 AM
To: lml@lancaironline.net
Subject: [LML] IV-P Hydraulic Pressure Switch

A few weeks ago when returning home my main landing gear failed to extend. I have determined the pressure switch that controls the hydraulic pump relay has failed. The kit supplied switch has a minimum temperature rating of -22 deg F. Since my switch failed with about 110 hrs on it, has anybody found a better switch?

On a personal note: When building N7VG, the only thing my wife wanted was her own personal landing gear lights. She was all over the fact that the mains did not lock down. The emergency pump worked and all is well.

Craig Berland

IV-P N7VG