Hi everyone, I know I saw some information on internal fuel pumps as
opposed to
external pumps. But can't find the emails. Paul I believe it was you who
said the
internal pump would be better for the P Port fuel injected engine. Let me
get to the
question I'm in the process of building my first tank and think if I'm
going to
install an internal tank I should make provisions for it now. How ever
I'm not sure
what that entails. Any feed back here would be greatly appreciated.
Thanks T.W.
Internal pumps are nice as you never have to worry about prime or vapor
lock.
Trouble is you need two in each tank as a back up. You also need an access
panel
large enough to get them in and out.
I assume this is a low wing airplane.
Paul Lamar ...No rotor no motor.
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RV8A, Leading edge tanks, two in each tank will make it tight. Getting
them in and
out through the planned access panel would mean dropping a wing to replace
the pump.
How should they be connected electrically, two separate switches for the
back ups,
or both run all the time when on that tank. And the plumbing, they
should feed a
single line out of the tank? So that means check valves between pumps and
the suction
lines will be separate? So many questions, I'm pretty sure I can
construct the tank
with the exception of the rear baffle and inside rib while I work out the
details and
that way I can move on to the right wing.
Paul what size of pump for the pport, Tracy sells the 95 PSI pump for
$121. But I
believe that is and external pump. I need to pump a minimum of 33 gal per
hour for
full power I think. So if I use two pumps per tank then I could use
smaller pumps.
What if I used a single internal pump for the primary and an external pump
for the
secondary. Could I pull fuel through the failed pump? I could easily
mount the
secondary on the firewall. Would fuel push through the secondary with out
to much
pumping loss. Yeah I think I'm over my head here. I'll have to make some
sketches
to figure this out. Stand by for more questions. Thanks T.W.
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Well at 250 HP level you will need about 30 gallons an hour.
Both right and left tank pumps can be on for takeoff with the four pump
system.
Two switches, center off up for primary and down for back up could be used
to select
the primary or the backup pumps. One switch for the right tank and the
other for the
left tank. The pumps should have one way valves built in to the output
side. Most do.
as a backup you can install two one way valves out side the tanks before
the supply
lines are teed together. You tee the outputs together in the tank or
outside the tank and then tee the outputs again to the high pressure fuel
rail.
Do not attempt to use dynamic pressure type vents to help the flow.
In other words vents facing forward into the air stream.
In some case over about 150 MPH dynamic pressure can force fuel through
the system and out the other tank's vents.
The return flow MUST be switched with a valve back to the tank you are
drawing
fuel from. VERY IMPORTANT! If you don't you can empty a tank in
a matter of a just few minutes by pumping fuel overboard through the vents
in the tank not selected.
DO NOT use a header tank with the return fuel going to the header tank
with this system. The header tank will be pressurized to 50 psi and the
return flow system WILL NOT WORK. Beside that a header tank would have to
be very robust indeed to withstand 50 psi.
Another advantage of the four pump system is the plumbing is about
as simple as one can get with a high pressure fuel system.
Red is return flow and green is supply.
External high pressure pumps might work but they are VERY VERY sensitive
to
restriction or lack of head on the intake side. Not good on a low wing
airplane.
CAUTION! High pressure fuel systems are complicated and subtle. All
scenarios
must be investigated very carefully indeed.
Paul Lamar
Hi Paul
I tested Tracy's pumps from new, bone dry, they will suck up over 1
American foot, they may do more but that is where the jerrycan was.
I don't like the idea of two pumps in the RV tanks. Too much to go wrong.
If I ever built another plane I would forget about fuel injection and go
super simple slide carby and one low pressure pump.
Ian Beadle.
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