Return-Path: Received: from [65.33.166.39] (account ) by logan.com (CommuniGate Pro WebUser 4.1.1) with HTTP id 2536912 for lml@lancaironline.net; Thu, 21 Aug 2003 19:21:56 -0400 From: "Marvin Kaye" Subject: Re: [LML] LNC2 and Legacy gear To: lml X-Mailer: CommuniGate Pro WebUser Interface v.4.1.1 Date: Thu, 21 Aug 2003 19:21:56 -0400 Message-ID: In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1"; format="flowed" Content-Transfer-Encoding: 8bit Posted for "Christopher Zavatson" : With a properly assembled hydraulic pump, the most pressure a leak from the high to low side can generate in the low side circuit is about 150 psi. The key point is that the pump must be properly assembled. For a number of years they were not. The LNC2 pumps have a back pressure circuit that allows the extra fluid volume produced by the retracing cylinder rods to get back to the reservoir without causing hydraulic lock. If the back pressure circuit is not there or disabled due to an incorrectly installed spool valve, pressure on the low side builds until the low pressure relief valve opens. The relief valve setting is higher than the pressure switch and thus the switch is tripped/opened. Cracking the dump valve relieves this pressure momentarily so that the pump will start running again. If you install pressure gauges on the hydraulic lines and observe the readings during gear cycling with the spool valve installed incorrectly and correctly you can see the influence of the back pressure circuit and the spool valve orientation with regard to relieving pressure in the low pressure circuit. When everything is assembled properly and the gear is retracted, you can pump as much fluid into the low side circuit as you wish. It will not raise the pressure above the back pressure relief valve setting. It seems a miscommunication between Oildyne and Lancair led to the delivery of incorrectly assembled pumps for a couple of years. The pump schematic is available on-line at Oildyne's web site. Look up 108 Series Hydraulic Power Units. We use the "LB" circuit. Note that up/down and high/low are reversed as we use high pressure to retract the cylinder. The schematic assumes high pressure extends the cylinder. Chris Zavatson N91CZ 360 std