Return-Path: Received: from pop3.olsusa.com ([63.150.212.2] verified) by logan.com (CommuniGate Pro SMTP 3.5b8) with ESMTP id 953741 for rob@logan.com; Tue, 13 Nov 2001 11:28:14 -0500 Received: from smtp005pub.verizon.net ([206.46.170.184]) by pop3.olsusa.com (Post.Office MTA v3.5.3 release 223 ID# 0-71866U8000L800S0V35) with ESMTP id com for ; Tue, 13 Nov 2001 08:20:28 -0500 Received: from GCasey (calnet31-66.gtecablemodem.com [207.175.254.66]) by smtp005pub.verizon.net with SMTP for ; id fADDXNW07344 Tue, 13 Nov 2001 07:33:23 -0600 (CST) Reply-To: Reply-To: lancair.list@olsusa.com From: "Gary Casey" To: Subject: fuel pump routing Date: Tue, 13 Nov 2001 05:32:39 -0800 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Importance: Normal In-Reply-To: <20011113064422.AAA27953@pop3.olsusa.com> X-Mailing-List: lancair.list@olsusa.com <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> << Lancair Builders' Mail List >> <<<<<<<<<<<<<<<<--->>>>>>>>>>>>>>>> >> >>Is it better to plumb these two pumps in series (does the "off" pump flow through enough) or parallel (does the "off" pump check the reverse flow)? Are there any redundancy issues that makes one installation safer over the other?<< I think the answer depends on what type of fuel pumps they are. If you are building a carbureted engine and using constant-pressure pumps I believe in the parallel arrangement. I once suffered an unscheduled landing because of the series arrangement in my Cherokee. But if you put them in parallel I would recommend two separate strainers to make the fuel system totally redundant (except for the selector valve). My problem was that both pumps flowed through a single strainer, which plugged up with ice crystals. With the pumps in parallel the fuel pressure will stay roughly constant and the flow will be limited by the float valve in the carburetor. If the second in line is a mechanical pump its diaphragm will cease to stroke, effectively shutting it off. But if the problem is a ruptured diaphragm it will still leak. For fixed displacement pumps used in automotive fuel injection systems I would recommend putting the pumps in series with a check valve paralleling each. In this way the flow will remain constant with either or both pumps running and the check valves will allow the fuel to bypass the inoperative pump. Gary Casey Lancair ES project >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> LML website: http://members.olsusa.com/mkaye/maillist.html LML Builders' Bookstore: http://www.buildersbooks.com/lancair Please remember that purchases from the Builders' Bookstore assist with the management of the LML. Please send your photos and drawings to marvkaye@olsusa.com. >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>