Perry wrote:
If you are flying and running only one h.p. fuel pump,
and that pump fails, the engine will become silent only milliseconds later!
This is
interesting. As my circuit diagram is currently configured, I have a
pressure switch in the fuel system which automatically turns on the backup
pump if the pressure drops below about 30 psi. (don’t remember now the exact
setting on the pressure switch). Do you suppose that this wouldn’t react
fast enough to keep the engine running?
There is a
manual bypass so I can turn the pump on if I want. The idea was to turn
on both pumps for takeoff, but at other times the backup would automatically
kick in to keep the engine from stopping if the primary pump stopped; thereby
avoiding rapid heart rates on the part of pilot and
passengers.
Al
Al,
I think that your set up should preclude rapid heart rates for the most
part. Being a switch, if it is set for around 30 psi fuel pressure then
your back-up pump should kick in immediately if pressure falls below that
point. With a pump that can pump 45 lbs/hour or 4.5 gallons/min at 43
psi then it should not take it any appreciable time to fill and
repressurize the fuel rails and hoses.
I am
assuming you are using AN-6 lines and assuming you have a total of 4 feet of
it in your high pressure part of your fuel system. Then at 3/8" ID you
have approx 5.3 cubic inches (if it were completely empty - which it shouldn't
be when you backup pump kicked on) that amounts to around 0.02294
gallons. So at 4.5 gallons/min the time to fill that volume would be
0.02294/4.5 = 0.0051 minutes or around 0.306 seconds. And
that is if the pump turned on after the lines were completely empty. So
I don't think you would notice it during normal operations. You might
notice the engine changing tone as the fuel mixture started to lean but I
think that would be about it.
Ed
Anderson