Today's Message Index:
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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)
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Subject: | 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
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Subject: | Re: Auto Aux Fuel Pump Circuit Idea |
At 08:25 AM 12/9/2011, you wrote:
><aerobubba@earthlink.net>
> 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
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Subject: | Re: Auto Aux Fuel Pump Circuit Idea |
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
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