<< > Wow Ed!!,...........Talk about simplicity. I think
 > it's "BRILLIANT", sure beats all that extra
 > valving/plumbing............Any comments on this guys?
 >
 >                                        Butch Diaz Sr. >>

How much current does your fuel pump draw Ed?  At idle nearly 100% of

that

energy is going into heating the circulating fuel.  There is also
considersable heat picked up from the engine compartment and fuel rail.

A

simple calculation will tell how long you can idle until the fuel boils.

Jeff Spitzer

Jeff,
    I agree that with the unused and heated fuel being returned to the
header tank inside the cowling (without first flowing back to the wing tank
heat sink) can result in vapor pressure build up.  A small amount of fuel is
of course used even at idle, so some amount of cool fuel is being drawn into
the header tank at idle, but a minimal amount.  If I had it to do over, I
would still used the header tank arrangement, but would place the header
tank in the gap between the wing skin and fuselage (or some other location)
to reduce heat build up from the engine/exhaust.

.  Early on using Auto Gas and on a hot day during hard ground run-up, I
would see surges in the fuel pressure (indicating vapor pressure
fluctuations - I believe), turning on the boost pump which provides 6 psi
pressure to the header tank always eliminated the surges.   I have since
added a cooling (2" dia)  duct blowing outside air on the pumps and header
tank.   I also now use aviation gas (for another reason - an aircraft fire
during refueling using approved containers  of auto gas apparently  ignited
by static electricity) which together with the added cooling duct appears to
have eliminated those symptoms.

  However, to answer your question, the pumps specs indicate they draw 5.8
amps at 12 volts.  I have two parallel pumps but normally only use both
during take-off and landing during which I also have the boost pump on.

 Again, if an individual should decide to use a similar  type of system, I
agree that vapor lock is a potential hazard and steps must be taken to
preclude/minimize that possibility. I was looking for simplicity and
reduction in lines and switching valves which this approach permits appealed
to me.

Ed

Ed Anderson
Matthews NC

 
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