Return-Path: Sender: (Marvin Kaye) To: lml@lancaironline.net Date: Thu, 11 Mar 2004 10:29:38 -0500 Message-ID: X-Original-Return-Path: Received: from mta-out-1.udlp.com ([207.109.1.8] verified) by logan.com (CommuniGate Pro SMTP 4.1.8) with ESMTP id 3074082 for lml@lancaironline.net; Thu, 11 Mar 2004 10:10:20 -0500 Received: from asdmngwia.mpls.udlp.com (asdmngwia.mpls.udlp.com [10.1.62.22]) by mta-out-1.udlp.com (8.12.10/8.12.10) with ESMTP id i2BDftBb030053 for ; Thu, 11 Mar 2004 07:41:55 -0600 Received: from DM-MN-06-MTA by asdmngwia.mpls.udlp.com with Novell_GroupWise; Thu, 11 Mar 2004 09:10:16 -0600 X-Original-Message-Id: X-Mailer: Novell GroupWise Internet Agent 6.0.1 X-Original-Date: Thu, 11 Mar 2004 09:10:05 -0600 From: "Christopher Zavatson" X-Original-To: Subject: Possible Gear Hydraulic System Vapor Lock Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Content-Disposition: inline Hollis, The component preventing your hydraulic pump from extending the gear is = the pressure switch. It is either encountering enough pressure to open or = is stuck open. Given that you have replaced the switch, let's assume the = switch is not sticking. The case you describe of trying to lower the gear = while it is retracting is the easiest test to see if your spool valve is = installed backwards. Your results of this test indicate that it is indeed = backwards. To be 100% sure without taking the pump apart, you can put a = pressure gauge in the down circuit. During retraction you should see = virtually no pressure. Another, even easier but not so scientific, method = is to measure the resistance across the down pressure switch to determine = if is remaining open during the retraction cycle. If the spool valve is = in backwards you will read the relief valve pressure setting for the down = circuit during the retraction cycle. =20 The purpose of the spool valve is twofold. First it pushes the poppet = valve, which is retaining system pressure, off it's seat allowing fluid to = return to the pump. Secondly, for the retraction stroke, it allows the = rod volume to return to the reservoir without restriction. If this path = is not available, the rod volume must push past the pressure relief valve = in the down circuit. Your high pressure circuit is then actually = pressurizing the low pressure circuit and opening the down side pressure = switch. There is another very rare scenario where the pump turns on for a fraction = of a second and then stops, but based on your description of the ground = test in particular the spool valve seems like a likely culprit. A large = number of pumps are known to have been built up incorrectly. Chris Zavatson N91CZ 360std Christopher Zavatson Mobility Technologies United Defense (408)289-4329