---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Fri 12/09/11: 3 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 06:29 AM - Re: Auto Aux Fuel Pump Circuit Idea (Glen Matejcek) 2. 11:06 AM - Re: Re: Auto Aux Fuel Pump Circuit Idea (Robert L. Nuckolls, III) 3. 12:26 PM - Re: Auto Aux Fuel Pump Circuit Idea (jonlaury) ________________________________ Message 1 _____________________________________ Time: 06:29:27 AM PST US From: Glen Matejcek Subject: AeroElectric-List: Re: Auto Aux Fuel Pump Circuit Idea HI John- I once had a Rabbit that developed a rather annoying habit of sputtering and quitting at random and inconvenient times and locations on hot days, and it seemed like vapor lock was the culprit. The dealer could find nothing wrong with the car and insisted I was buying crap gas. So, I took it to a sharp independant mechanic (a pilot, as it happens) who determined that when my tank mounted fuel pump got hot, it failed. When cooled sufficiently, it would function and test normally. However good and predictable modern pumps may be, my fundamental premise remains that if normal operations can require the use of both pumps to keep the engine running, there is in fact no redundancy. Finding myself at the side of the road amongst the cornfields in the Rabbit was a nuisance, in the RV it would be a bit more problematic. Just one guy's perspective- >My queries and investigations into automotive hi pressure fuel pump failures revealed >that a fuel pump rarely has an abrupt total failure. The gearotor and vane >type premature failure of the pump mechanism itself is from dirty fuel. Motor >failure is age/time related the same as any certified, mechanical/electric >AC fuel pump. The symptoms of impending failure of automotive fuel pumps are >the same...falling pressure/increase amperage draw. But people being the fallible >monitoring system that they are, is the reason for redundant essential systems. > >Anecdotally, I have never experienced an automotive fuel pump failure inspite of >two Toyota trucks, a Ford Taurus, a Ford truck and a MBZ sedan being driven >over 1,000,000 miles. > >John > Glen Matejcek ________________________________ Message 2 _____________________________________ Time: 11:06:48 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: Re: Auto Aux Fuel Pump Circuit Idea At 08:25 AM 12/9/2011, you wrote: > > So, I took it to a sharp independant mechanic (a pilot, as it > happens) who determined that when my tank mounted fuel pump got > hot, it failed. When cooled sufficiently, it would function and test normally. > >However good and predictable modern pumps may be, my fundamental >premise remains that if normal operations can require the use of >both pumps to keep the engine running, there is in fact no redundancy. > >Anecdotally, I have never experienced an automotive fuel pump > failure inspite of > >two Toyota trucks, a Ford Taurus, a Ford truck and a MBZ sedan being driven > >over 1,000,000 miles. I've experienced two pump failures . . . on the same vehicle. It was a generic design common to millions of other vehicles. "Reliability studies" that speak to 1 failure per bazillion flight hours are statistically correct but often interpreted poorly. The explanation is pretty lengthy and easily accesses elsewhere. This is why your's truly has always encouraged builders to assume that EVERY component is going to fail at some point in your lifetime experience with the airplane. Then run the failure mode effects analysis to determine how that failure can be accommodated . . . as opposed to anointing it with the holy-oil of prevention. See chapter 17 of "the Connection". With respect to fuel pumps, any time you can integrate a modern FACET pump into your design, you've got a big step up in service life. One moving part, two simple valves, totally sold state management of the energy used to compress the pumping spring. We discussed these pumps at length some years ago here on the lists. I researched the patents that spoke to the evolution of this technology dating back to the 20's. You can tiptoe through the patents on this style of pump at: http://www.aeroelectric.com/Mfgr_Data/Pumps/ The neat thing about modern incarnations of this style is elimination of the breaker contacts found in the earliest versions. Another nice feature is their ability to simply shut down when fluid flow is restricted of stopped of hard. Fuel pressure is a function of a compressed spring force and not stalled rotor current. One would be hard pressed to find a pump more friendly to the failure modes effects analysis for moving fuel around the airplane. Bob . . . ________________________________ Message 3 _____________________________________ Time: 12:26:41 PM PST US Subject: AeroElectric-List: Re: Auto Aux Fuel Pump Circuit Idea From: "jonlaury" nuckolls.bob(at)aeroelect wrote: > At 08:25 AM 12/9/2011, you wrote: > > > > > > > > > > > > > So, I took it to a sharp independant mechanic (a pilot, as it > > happens) who determined that when my tank mounted fuel pump got > > hot, it failed. When cooled sufficiently, it would function and test normally. > > > > However good and predictable modern pumps may be, my fundamental > > premise remains that if normal operations can require the use of > > both pumps to keep the engine running, there is in fact no redundancy. > > > > > > > > > > > > One would be hard pressed to find a pump more > friendly to the failure modes effects analysis > for moving fuel around the airplane. > > > > Bob . . . Glen and Bob, No argument with either of you. I appreciate both of your observations. The Facet solid state pumps are hard to beat and I have one as a transfer pump. But they don't make the high pressure required by EFI. And Glen, of course, if you need two pumps for a system, there is no redundancy if only two are installed. My system needs one operable pump. Two are installed in the hopes that I will be able to choose a runway over a freeway as a place to land if the primary pump dies. I was glad when this subject came up as it gave me the opportunity to put my fuel system on the table for the analytical minds that hang out here. John Read this topic online here: http://forums.matronics.com/viewtopic.php?p=360561#360561 ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.