Today's Message Index:
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1. 05:56 AM - Re: fuel return line? (Thom Riddle)
2. 06:49 AM - Re: fuel return line? (Roger Lee)
3. 11:44 AM - Re: Fuel return line (Roger Lee)
Message 1
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| Subject: | Re: fuel return line? |
The certificated engine installations, like in my Katana, have the return line
for the carbureted engines. The primary purpose is to preclude vapor lock.
Plumbing back into the supply line is not the same as running the return line back
to the gascolator, particularly if you have an electric backup fuel pump between
the tank and the "tee". In this case, you will be pressurizing both sides
of the fuel system when the electric pump is running. I suppose you could put
a check valve in the return line to fix that. Running back to the gascolator
returns the excess fuel back to unpressurized ambient pressure location.
In experimental or other non-certificated installations, if your operating environment
(not high altitude, not intense heat) does not encourage vapor lock, then
adding a return line is not absolutely necessary. If you do operate in these
potential vapor lock conditions, running your electric fuel pump will help
reduce the risk by pressurizing the supply line up to the mechanical pump.
Back in the dark ages when I was a drag racer, an electric fuel pump at the tank
outlet generally resolved vapor lock issues on hot sunday mornings at the drag
strip.
--------
Thom Riddle
Buffalo, NY (9G0)
Kolb Slingshot SS-021
no engine
FOR SALE
Diamond Katana DA20-A1
Rotax 912 F3
Don't worry about old age... it doesn't last very long.
- Anonymous
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Message 2
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| Subject: | Re: fuel return line? |
Hi Guys,
Do not return the fuel re-circulation line back into the fuel feed line. If you
are using a new Rotax fuel pump then you will absolutely need the re-circulation
line and even if you don't have that pump now your old pump can go at anytime
and then you'll be using the new pump. It is easy enough to install the re-circulation
line. It helps control vapor lock and over pressure. By the way the
new Rotax max fuel pressure is no longer 5.8, but 6.2 psi. If you have a Dynon
EMS or some other EMS with fuel pressure limits then it is a good idea to
reset the red line fuel pressure to a higher value.
--------
Roger Lee
Tucson, Az.
Light Sport Repairman - Maintenance Rated
Rotax Repair Center - Heavy Maint. Rated
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056
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Message 3
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| Subject: | Re: Fuel return line |
Hi John,
Here's the issues.
Many of the planes from yesteryear wasn't a problem. They were open air engines
so hot fuel lines weren't an issue and the old style fuel pump didn't have enough
excess pressure to be an issue. Come up to date with many of the newer LSA
and Experimental aircraft with nice tight cowls and then throw in on top of
that too many owners fail to install the fuel and oil lines in fire sleeve then
heat inside the cowl makes a night a day difference. Vapor lock. I see it alot
now days with tight cowls. Fire sleeve not only protects from fire, but helps
with excessive heat too. Now comes along the new Rotax fuel pump that puts
out more pressure and then add on top of that someone who likes to run an electric
pump all the time which adds
.5 -1.0 psi more and the fuel then can't be controlled by the float needle valve
and it pukes out the vents all over a hot engine, on hot exhaust manifolds
because some didn't bother to install carb drip trays and now we have an issue.
Now add that owners haven't rebuilt or replaced an older float needle valve
and now we definitely puke fuel and the engine runs rough.
Just a side note* Exposed fuel lines outside of fire sleeve tend to deteriorate
faster than fire sleeved fuel lines.
So the bottom line is application is everything and sooner or later your old pump
will die and the new pump is all that is available. It's so easy to add the
re-circulation line and never have to look back. On any flight the float needle
valve can start leaking then you have the issue too.
--------
Roger Lee
Tucson, Az.
Light Sport Repairman - Maintenance Rated
Rotax Repair Center - Heavy Maint. Rated
Home 520-574-1080 TRY HOME FIRST
Cell 520-349-7056
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=397863#397863
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