X-Virus-Scanned: clean according to Sophos on Logan.com X-SpamCatcher-Score: 50 [XX] Return-Path: Sender: To: lml@lancaironline.net Date: Tue, 17 Apr 2007 22:44:01 -0400 Message-ID: X-Original-Return-Path: Received: from smtp4.na.baesystems.com ([63.164.202.13] verified) by logan.com (CommuniGate Pro SMTP 5.1.8) with ESMTP id 1990638 for lml@lancaironline.net; Tue, 17 Apr 2007 21:41:40 -0400 Received-SPF: none receiver=logan.com; client-ip=63.164.202.13; envelope-from=Christopher.Zavatson@baesystems.com Received: from smtp2.na.baesystems.com (smtp2.na.baesystems.com [10.40.96.13]) by smtp4.na.baesystems.com (8.13.6/8.13.6) with ESMTP id l3I2eAOQ007538 for ; Tue, 17 Apr 2007 22:40:10 -0400 (EDT) Received: from GLDMS00006.goldlnk.rootlnka.net ([10.44.64.12]) by smtp2.na.baesystems.com (8.13.6/8.13.6) with ESMTP id l3I1efJc000699 for ; Tue, 17 Apr 2007 21:40:46 -0400 (EDT) Received: from gldms10602.goldlnk.rootlnka.net ([10.64.39.19]) by GLDMS00006.goldlnk.rootlnka.net with Microsoft SMTPSVC(6.0.3790.1830); Tue, 17 Apr 2007 21:40:41 -0400 Received: from GLDMS10607.goldlnk.rootlnka.net ([10.64.39.20]) by gldms10602.goldlnk.rootlnka.net with Microsoft SMTPSVC(6.0.3790.1830); Tue, 17 Apr 2007 18:40:40 -0700 X-MimeOLE: Produced By Microsoft Exchange V6.5 Content-class: urn:content-classes:message MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="----_=_NextPart_001_01C7815A.91DD303A" Subject: RE: [LML] Re: Gear Trouble X-Original-Date: Tue, 17 Apr 2007 18:40:39 -0700 X-Original-Message-ID: In-Reply-To: X-MS-Has-Attach: X-MS-TNEF-Correlator: Thread-Topic: [LML] Re: Gear Trouble Thread-Index: AceBVfoLsptcodWRTbSPdyUCwaTZOQAAjuSQ References: From: "Zavatson, Christopher J \(US SSA\)" X-Original-To: "Lancair Mailing List" X-OriginalArrivalTime: 18 Apr 2007 01:40:40.0793 (UTC) FILETIME=[927B1C90:01C7815A] This is a multi-part message in MIME format. ------_=_NextPart_001_01C7815A.91DD303A Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable =09 <> Scott, 'Splain that Lucy? My name ain't Lucy, but here is what you are seeing. The pressure switch is located very close to the pump. While the pump is running the pressure right at the pump is higher than anywhere down stream in the system due to losses incured by the flowing hydraulic fluid. This pressure gradient is a function of how many feet of hose and line and the number of fittings etc you have. After pump shut down, flow stops, pressure equalizes, hoses and such stretch into their final pressurized dimension and what happens? Pressure back at the pressure switch drops enough to cause the pump to turn back on. Pumps I use on the test bench need a much lower pressure switch setting because there is very little pressure bleed down after the pump stops. With only one cylinder and four feet of aluminum line and hose there is very little line loss, a very small pressure gradient and very little material to stretch. Scott, turn your pressure switches up just a hair and everything will tuck away on the first try. Chris =20 =20 =20 Chris Zavatson N91CZ 360std www.N91CZ.com ------_=_NextPart_001_01C7815A.91DD303A Content-Type: text/html; charset="us-ascii" Content-Transfer-Encoding: quoted-printable
<<Consider that if = the=20 spool/shuttle valve is stuck in some bad spot and the pressure is = equally very=20 high on both sides so that the dump valve cannot release the pressure, = there may exist problems with the relief valves.  = Besides that,=20 some of us have symmetric spool valves and some of us have offset = ones. =20 It is hard to install the symmetric ones backwards.
 
Peculiar pressure build ups associated with heat expansion may = also be=20 associated with the pump relief valves.  Mike Reinath claims that = his=20 relief valves operate differently when the pump runs.  He has = adjusted=20 his to be close to the pressure valve action.
 
The pump manufacturer claims that the relief valves should be set = about=20 400 psi higher than the circuit requirement.  Theoretically, the=20 manufacturer has set the relief valves for about 1000 (600 lo = pressure)=20 and 1500 (1100 hi pressure).  Also remember that pressure = switches have a=20 dead band - I.E. it may be triggered (to open) at the high side of its = pressure setting and the pump may continue to run long enough to raise = the=20 pressure even more.  Then, the pressure switch may not close=20 again until the pressure has dropped several hundred psi below = its=20 setting.  Or, maybe not.  Hydraulic logic is not precise in = this=20 application.
 
In my case, gear up operation frequently pauses before another = blip=20 finally tucks away everything nice and tight.  Why?  Because = a spike=20 opens the pressure switch prematurely and a few seconds = later, =20 pressure has degraded enough to re-activate the switch.  A leak, = you=20 say?  No, because that ultimately sucked up gear will remain = up=20 tight for days whilst the plane is on jacks.  'Splain that = Lucy? =20 Or, is it because that wild and crazy nose gear gas spring behaves=20 differently at the end of a fast retract, then relaxes a=20 bit after it is compressed for a few seconds and that causes a = slight=20 drop in the "hold it all up" pressure?  Is it my Karma?
 
Perhaps you should set your gear down pressure switch to a bit = higher=20 pressure.  Perhaps you should install a pressure switch bypass = switch as=20 some have done.  I dunno.  The current dump valve resolution = doesn't=20 seem too bad when the occasional problem occurs.>>
Scott,
'Splain = that=20 Lucy?
My name = ain't Lucy, but=20 here is what you are seeing.
The = pressure switch is=20 located very close to the pump.  While the pump is running the = pressure=20 right at the pump is higher than anywhere down stream in the system = due to=20 losses incured by the flowing hydraulic fluid.  This pressure = gradient=20 is a function of how many feet of hose and line and the number = of=20 fittings etc you have.  After pump shut down, flow stops, pressure=20 equalizes, hoses and such stretch into their final pressurized = dimension=20 and what happens?  Pressure back at the pressure switch = drops=20 enough to cause the pump to turn back on.  Pumps I use on the = test=20 bench need a much lower pressure switch setting because there = is very=20 little pressure bleed down after the pump stops.  With only = one=20 cylinder and four feet of aluminum line and hose there is very little = line loss,=20 a very small pressure gradient and very little material to=20 stretch.
Scott, turn = your pressure=20 switches up just a hair and everything will tuck away on the first=20 try.
Chris
 
 
 
Chris = Zavatson
N91CZ
360std
www.N91CZ.com
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