X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml Date: Thu, 23 Nov 2006 09:27:39 -0500 Message-ID: X-Original-Return-Path: Received: from web54309.mail.yahoo.com ([206.190.49.119] verified) by logan.com (CommuniGate Pro SMTP 5.1.2) with SMTP id 1595598 for lml@lancaironline.net; Wed, 22 Nov 2006 23:28:22 -0500 Received-SPF: none receiver=logan.com; client-ip=206.190.49.119; envelope-from=randylsnarr@yahoo.com Received: (qmail 49306 invoked by uid 60001); 23 Nov 2006 04:28:02 -0000 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.com; h=Message-ID:Received:Date:From:Subject:To:In-Reply-To:MIME-Version:Content-Type:Content-Transfer-Encoding; b=JUbxfGyDlTyzR/IuDPr5KxLUwcsps0pJ5f1Hs3cXxaetlaZ8+zelqojQEW3jW0O+6/3WFNsRjNRJMNxXGkLWB+qtbkuRWcVvd+z3Hawch+vyK4DBSLXSXwvpC+s/BUA+FCaD7uc8qoCj/n2g+MnHd97p1H2eV9/m0ajHs+lk8pk= ; X-Original-Message-ID: <20061123042802.49304.qmail@web54309.mail.yahoo.com> Received: from [67.50.40.154] by web54309.mail.yahoo.com via HTTP; Wed, 22 Nov 2006 20:28:02 PST X-Original-Date: Wed, 22 Nov 2006 20:28:02 -0800 (PST) From: randy snarr Subject: Re: [LML] Re: Electrical /Hydraulic system questionslancair235/320 X-Original-To: Lancair Mailing List In-Reply-To: MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="0-532984938-1164256082=:48838" Content-Transfer-Encoding: 8bit --0-532984938-1164256082=:48838 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Bob, You describe the exact same thing as I am experiencing. I have pressure gauges on the high and low side. In my case, both the high an low sides sometimes creep up in pressure during flight. Just today I noticed everying normal after takeoff 1300 high and 0 on the low. After 20 mins or so the high was 1700 or so and the low was 400. Gear came down normally. If the low side reaches 600 psi the gear will not come down without cycling the dump valve. I theorize that the down side pressure switch shuts off the pump because of this pressure. Ironically, The first time this happened was when I flew to the last labor day fly in at Redmond. It has happened several times since. I also noticed one day when I pulled the airplane out of the cool hangar and parked it out in the warm sun for an hour. When I got in the low side was very high and the high side was not far behind it. It alarmed me enough that I opened the dump valve and equalized the 2 sides. Don't remember what the pressures were. They equalized at something above 0. Maybe around 6-700 psi. It seems like increased heat increases pressure in the entire system. I am going to check the dipstic(not the pilot) and make sure it is not tight. I believe mine is. To answer your question about what the down side pressure is during retraction, it is running around 200 psi. The upside is 0 when the gear is being lowered. Thanks for the input... Randy,. "Bob B." wrote: : The fluid circuit is really a closed loop. The only options for returning fluid to the reservoir are either through one of the pressure relief valves or the low resistance back pressure circuit. Excess fluid needs to return to the tank every time the rod volume displaces fluid volume. When the rod volume is removed from the system, make up fluid is pulled in from the tank through a one way check valve. During retraction, the spool valve opens a low resistance path from the low side to the reservoir, eliminating a large pressure build up in the low circuit during retraction. - which also eliminate the possibility of pressure build up due to thermal influence. One side effect of the correct spool valve orientation and a leak free system is that you cannot manually push the gear up even with the dump valve open unless the spool valve is moved into the retract position. After opening the valve you still have a closed loop from high to low that is now bypassing the pump. When you try to push the gear up you get hydraulic lock. You are trying to add the rod volume to a closed system and the only route back to the reservoir is through a relief valve. By bumping the pump in the up direction, even with the dump valve open, you can push the spool valve into the retract position which opens up the low resistance path to the reservoir for the low side circuit. If you are able to push the gear up at all without bumping the pump, I would suspect the spool valve is backwards. Let us know what observe in the low circuit during retraction. You can also try the direction-reversal test during retraction. The response should be instantaneous. good luck Chris, It would seem that there is no one answer for this problem. On my 235, with the plane on jacks; I can open the dump valve and easily push any of the gear up. Spool valve is backward? When I do the direction reversal test the gear reverses instantly. Spool valve is OK? When I put the gear up and then open the dump valve, all 3 drop within 2-3 seconds. Years ago, I experienced a few instances of the gear not coming down when the gear switch was put down. This situation was always relieved by briefly opening the dump valve. It stopped happening, so I did not change anything. Am I just lucky, or what? Bob Belshe Moraga, CA Lancair 235/320 http://home.comcast.net/~rbelshe/ -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.1.409 / Virus Database: 268.14.11/543 - Release Date: 11/20/2006 --------------------------------- Everyone is raving about the all-new Yahoo! Mail beta. --0-532984938-1164256082=:48838 Content-Type: text/html; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Bob,
You describe the exact same thing as I am experiencing.
I have pressure gauges on the high and low side. In my case, both the high an low sides sometimes creep up in pressure during flight. Just today I noticed everying normal after takeoff 1300 high and 0 on the low. After 20 mins or so the high was 1700 or so and the low was 400. Gear came down normally. If the low side reaches 600 psi the gear will not come down without cycling the dump valve. I theorize that the down side pressure switch shuts off the pump because of this pressure.
Ironically, The first time this happened was when I flew to the last labor day fly in at Redmond. It has happened several times since. I also noticed one day when I pulled the airplane out of the cool hangar and parked it out in the warm sun for an hour. When I got in the low side was very high and the high side was not far behind it. It alarmed me enough that I opened the dump valve and equalized the 2 sides. Don't remember what the pressures were. They equalized at something above 0. Maybe around 6-700 psi. It seems like increased heat increases pressure in the entire system. I am going to check the dipstic(not the pilot) and make sure it is not tight. I believe mine is.

To answer your question about what the down side pressure is during retraction, it is running around 200 psi. The upside is 0 when the gear is being lowered.

Thanks for the input...

Randy,.

"Bob B." <rbelshe@comcast.net> wrote:
:
The fluid circuit is really a closed loop.  The only options for returning fluid to the reservoir are either through one of the pressure relief valves or the low resistance back pressure circuit.  Excess fluid needs to return to the tank every time the rod volume displaces fluid volume.  When the rod volume is removed from the system, make up fluid is pulled in from the tank through a one way check valve.  During retraction, the spool valve opens a low resistance path from the low side to the reservoir, eliminating a large pressure build up in the low circuit during retraction. - which also eliminate the possibility of pressure build up due to thermal influence.
One side effect of the correct spool valve orientation and a leak free system is that you cannot manually push the gear up even with the dump valve open unless the spool valve is moved into the retract position.  After opening the valve you still have a closed loop from high to low that is now bypassing the pump.  When you try to push the gear up you get hydraulic lock.  You are trying to add the rod volume to a closed system and the only route back to the reservoir is through a relief valve.  By bumping the pump in the up direction, even with the dump valve open, you can push the spool valve into the retract position which opens up the low resistance path to the reservoir for the low side circuit.  If you are able to push the gear up at all without bumping the pump, I would suspect the spool valve is backwards.  Let us know what observe in the low circuit during retraction.  You can also try the direction-reversal test during retraction.  The response should be instantaneous.
good luck
Chris,
 
 It would seem that there is no one answer for this problem.
 
On my 235, with the plane on jacks;
 
I can open the dump valve and easily push any of the gear up.    Spool valve is backward?
 
When I do the direction reversal test the gear reverses instantly.   Spool valve is OK?
 
When I put the gear up and then open the dump valve, all 3 drop within 2-3 seconds.
 
Years ago, I experienced a few instances of the gear not coming down when the gear switch was put down.  This situation was always relieved by briefly opening the dump valve.  It stopped happening, so I did not change anything.
 
Am I just lucky, or what?
 
Bob Belshe
Moraga, CA
Lancair 235/320  
http://home.comcast.net/~rbelshe/
 
 
 
 

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