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Hi Alan,
You wrote,
*WITH
NO SPECIFIC KNOWLEDGE*, it does seem that because the Dukes pump is *pre* the
engine, that too much fuel really can't happen, it's metered by the fuel divider
and if the throttle body is not open, then the fuel is returned via the return
line. So in effect you are just pumping fuel back into the tanks via the
return line....
I think that assumption is not totally
correct. I have an IO-550 and I have tried the "hot start" technique of
running the boost pump on high with the mixture at cut-off and the throttle
closed. The idea is to circulate cool fuel through the mechanical fuel
pump and then return it to the fuel tank. I get a substantial amount
of fuel coming out the cylinder drains when I do that. So at least in my
case, high boost has enough pressure to overcome the relief valve in the
mechanical fuel pump and to provide fuel to the injectors. Another data
point is that shutting down my engine at the end of a flight by pulling my
mixture control to cut-off won't work if the boost pump is on low; the engine
keeps idling.
According to Flying Magazine's
September 2004 Aftermath column, a Bonanza with a TCM TSIO-520 crashed
shortly after takeoff probably because the pilot inadvertently had the boost
pump in the high position. According to the article, full power operation
with the boost pump on high would not cause an appreciable loss of power, but
(according to the NTSB) when manifold pressure is reduced below 24 inches, the
engine will quit.
Fuel system problems are a common cause of
experimental crashes. I would be extraordinarily wary about making any
change to my fuel system.
Best,
Dennis Johnson
Legacy, now flying
Major discovery: Flying is more fun
than building.
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