If that's the definition of
a sump system, then I do not have a sump system. I have a small EFI
tank with two internal EFI pumps, fuel return to this EFI tank. This
EFI tank is located where the gascolator is in the stock Long-EZ fuel
system. I have the complete stock Long-EZ fuel system otherwise with
L-R-OFF selector (no BOTH). I will not refer to my system as a sump
system in the future, to avoid misconception (and arguments).
You've said it yourself Jim in the past, that you've had many problems
with your sump system. Maybe sump systems and BOTH selectors just don't
belong on Rutan derivatives, as RAF itself has said. As you saw, a
Lycoming-powered EZ had an accident in 1995 just after takeoff (sounds
like Paul?) with such a system.
Jim S. wrote:
A sump tank renders L-R(-B) selector redundant
and superfluous. L and R selectors allow the fuel pump to "suck" fuel
from the selected tank. When the tank is empty, you select the other
tank. If you have "Both" selected and one goes empty, the pump sucks
air through that line. Either way, the engine quits when one tank goes
dry. You get power back by selecting the tank that has fuel in it.
The main disadvantage with a "Both" position has to do with distraction
and delay - when the engine quits, you have to figure out which tank is
dry and which way to turn the knob to select the tank that has fuel.
Takes time and is a definite failure mode. Gravity feeding a sump
through big enough lines eliminates the need for valves. That's the
main purpose of a sump. Selectors are for when you don't have a sump.
They have no place on a system that does. The Rutan derivatives with a
sump have no selector; those with a selector have no sump. Paul's
setup was unique.
Just a theory ... Jim S.
rijakits wrote:
The only safe way to have a "Both"-selection for a low wing
would be (IMHO), to have a low pressure pump in each tank feed a fairly
large sump ( 2 gallons +) with a system as described by Georges below:
EFI pump picking up at the bottom of the sump, with a return to
the top and baffels, not just separating the top from the bottom, but
also side from side, so when a tank pump starts to pump air into the
sump, it can vent to the top of the sump and out through the vent,
which would have to go to both main tanks.
With some additional cross-feed line from one tank to the other
with a manual valve, one could use one tank pump as the back-up for the
other:
Open the crossfeed valve and slip the plane accordingly for a
while. That should push the fuel into the other tank, in case one of
the pump fails.
One question remains: How would you prevent or equalize overflow
from the sump to the tanks?
Thomas J.
-----
Original Message -----
Sent:
Sunday, May 29, 2005 8:07 PM
Subject:
[FlyRotary] Re: will EFI pumps pump air was Re: Fuel Tank Selection
Group FWIW
Call it a sump or header tank, if its large enough say 3
liters oops! I mean quarts with both pumps picking up fuel at the
bottom 1/4 of the tank with the fuel return pointing at the cover to
avoid aerating the fuel in the header (possibly a baffle below it &
a vent pipe to each tank) Gravity feed would work in a high wing , in a
low wing I think you still need a low pressure transfer pump to push
fuel to the header tank from the mains. I don't think it is safe to
have "Both" position in the fuel selector except in a gravity system
with carburetors, not with EFI, the possibility of "sucking air "is
unavoidable without check valves ( more weight, more cost & more
possibility of problems).
Georges B. ( Not really stirring the pot, maybe just a
little)
-------Original
Message-------
Date:
05/29/05 17:42:01
Subject:
[FlyRotary] Re: will EFI pumps pump air was Re: Fuel Tank Selection
Now I'm not so worried, because each
high pressure fuel
pump draws from it's own tank and the only point of inter- connection
is where the lines join at the fuel rail(s).
This
brings up a question that I've had before, and I'm not
sure this is exactly what anyone is doing, so it's not meant that way.
Say
you have two tanks, with an EFI pump for each tank. You
then connect the output of each pump together, feeding into one line
running to the fuel rail. The question is: What happens when one
tank runs out of gas? Will the EFI pump move enough air through it to
disturb the fuel rail pressure that's being delivered from the other
pump, or would it just stop pumping at that point, and do no harm
(other than maybe burning the pump up eventually)?
Yep, still trying to
figure out how to fix my fuel transfer system.
Cheers,
Rusty
Lez_fuel_system.gif
|