The engine driven fuel pump on my 2180 VW will only flow fuel if the engine
is running. That's a safety feature of the pump originally designed for the
automobile installation. To get fuel to the engine for starting, I put a
check valve in parallel with the engine fuel pump; this bypasses the engine
pump so that the Facet electric pump can push fuel to the mechanical pump
and to the carb for starting the engine. After engine start I shut off the
Facet electric pump. The check valve prevents fuel from the outlet of the
mechanical engine fuel pump from going back to the inlet.
A back up, in case the engine fuel pump failed, would be pumping fuel to the
engine with the Facet electric pump alone. To know what is going on, the
fuel pressure sensor at the carb inlet sends info to the meter in the
cockpit; 3 psi for the engine pump and 5 psi for the Facet electric pump.
Those pressures will flow excess fuel of 21 gal/hr and 23 gal/hr
respectively during adverse attitude fuel flow tests.
I agree with Mark and Larry. Don't put the automatic fuel shut off function
in your KR installation. That's not needed and would be one more thing to
fail.
Sid Wood
Tri-gear KR-2 N6242
California, MD, USA
Dave McCauley wrote:
I'm installing a Facet electric fuel pump and want to use a Nason pressure
switch to shut the fuel off if oil pressure drops to near zero. I Need to
know the part number of the Nason switch.
-----------------------------------------------------------------------------------------------
You didn't ask for my opinion, but I caution you not do this. I say
that because I've flown something like 20 miles with zero oil pressure
on the meter. I made it back to the airport, but admittedly the prop
would barely turn after I pulled onto the apron at the hangar.
Replacing the crank and main bearings made it good as new. If I'd had
that switch in place, I'd have gone down in what passes for mountains
around here, completely wooded, and there probably would have still been
a fire.
Yes, you can put a bypass around the Nason switch as mitigation, but
will you remember that it's there in the "heat of the moment"? I
probably wouldn't. I've had several deadstick landings, and not once
did I remember to shut the fuel off at the tank. Yep, probably should
have read the checklist, but I didn't think to read that either....I was
too consumed with getting my butt back on the ground in one piece!
Really, if your oil pressure goes to zero, you should have a big red
flashing light in front of you to tell you (or say below 15 psi), and at
that point, can't you just switch off the pump in the regular way? If
you're going to shut off the fuel, you're clearly done flying, so why
not?
If I were going to do something like this fuel pump shutoff, I'd use the
fuel shutoff relay that was used on Rabbits/Golfs in the 70's and 80's,
and is likely still used in Golfs and other VWs today. I own several
VWs and Audis now, and I've never heard of one failing while driving.
Designed to minimize the fire during a car crash, it kills the fuel pump
when the tach signal is lost, taking the 70 psi fuel spray out of the
equation. I actually toyed with doing this, and got a relay, but never
completely warmed up to the idea. There's more on this, including a
part number, at http://www.n56ml.com/fuel/index.html , including a
schematic, near the bottom. If done as VW does it, operating the
starter provides power back to the fuel pump, as long as the key is in
the "start" position. So far I've lived without it, as I have a
completely redundant fuel pump / ignition power circuit in both KRs.
This is detailed on both the electrical system page and the fuel system
page, at http://www.n56ml.com/electrical/index.html.
I'm still not recommending this "fuel pump relay" either, as it's just
another potential failure point that I can live without.
Just my two cents worth, and I don't mean to rain on your parade....just
though I'd share my opinion....
Mark Langford, Huntsville, AL
ML "at" N56ML.com
www.N56ML.com
------------------------------
I was going to respond in much the same manner as Mark.? He has much
more experience with in flight emergencies than I do so I'll just ditto
his remarks.? My only comment is I don't want anything "automatic"
cutting off my fuel supply other than the on / off switch on the panel
and the fuel shutoff valves of which I'm totally in command off.? I'm
reminded of all the comments I hear about Airbus and the like where too
many options are taken away from and override the pilot's control.?
Anything that comes between me and the on / off switch limits my options
and simply induces another possible failure point.
The chances of you remembering to "turn on the second pump" if a system
shuts off your fuel reminds me of an incident a friend of mine had in
his RV10.? Flying low altitude in an air race his air intake was cut off
when a rubber tube collapsed.? He had two knobs on the panel and pulling
either one would have kept him in the air and running normal.? One was
carb heat and the other was intake air by-pass.? In the heat of the
moment he didn't pull either and ended up landing on a two lane paved
road.? All turned out well but he could have just as easily landed back
at the airport and correct the problem.
I have two Facet pumps, no gravity feed, and no engine driven pump.? I
lost my main electrical buss at altitude and lost the pumps.? I noticed
the failure when all my gauges went to zero and without thinking I
turned on the backup electrical system.? I'm not sure why / how I
reacted so quickly other than I had considered that possible failure
mode and designed a backup.? I'm guessing all the thought and planning I
had put in to that system allowed my brain to react without a conscious
decision.? Whatever it was I landed safely and corrected the problem.
As always, your results may vary.............
Larry Flesner
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