Hi Guys,

PRESSURE REG POSITION

Paul's installation is correct.  The regulator MUST be on the RETURN side of
the fuel rail.  Otherwise,  it can't regulate the pressure!!  The regulator
has to be able to dump excess pressure overboard to the fuel return,  and
the absolutely critical thing is that it must be able to keep the pressure
drop across the injectors constant
as the MAP (Manifold Absolute Pressure) varies. (otherwise you can't meter
the fuel accurately)

HIGH PRESSURE PUMP POSITION

Ideally,  the pressure pump(s) should be below the header/surge tank level.
They do not like sucking fuel up hill,  especially when an aircraft is
climbing at a steep angle - you are just asking for trouble.  In drag cars,
the pump is always positioned BEHIND the surge tank because the gravity
vector is rearward,  just like a climbing aircraft (which is when you need
the most fuel!!).

A word of warning.  With a header tank at the front in a steep climb,  I can
see a situation where a gravity fed header/surge tank could cease to be
filled.  Auxillary lift/boost pumps then become necessary.  Think about that
one ...

ONE WAY VALVES

If you are running two high pressure pumps,  and normally only use one for
cruise (but both for take-off),  they should have one way valves in front of
them.  Otherwise,  you won't get full pressure to the rail and the
regulator. The fuel will just reflux around back through the T piece to the
stationary pump and back into the header/surge tank.  Some pumps do have one
way valves in them as standard - easy to check before fitting -  just blow
through the outlet.

Additionally,  the idea of continually circulating fuel from the fuel rail
via the return line is to prevent vapour
lock from heat soak in the fuel rail.  All this is settled technology, and
has been around and working perfectly well, in millions and millions of EFI
cars, for over 20
years.  I continue to be flummoxed as to why Experimental aircraft people
are always trying to re-invent the wheel un-necessarily and cause themselves
grief?  Just copy what is known to work ...

RETURN LINES AND VENTING

Finally,  with the use of a header/surge/auxillary tank,  it MUST be vented.
The correct way to do it is to have the return line from the pressure reg
return to the side of the header/surge tank near the top.  Another line is
then returned from the very TOP of the header/surge tank to the main tank
(the idea is to be able to purge any air/vapour).  This way,  the
header/surge tank is vented via the main fuel tank(s),  and the header tank
always remains full.

The only caveat on this is obviously if you have multiple main tanks (one or
more in each wing),  the return lines to the tanks must be switchable.
Otherwise as you pump fuel out of either (any of the) tank(s),  and IF it
always goes back to the one tank,  it will overflow pretty quickly.  The
return line must therefore go back to the tank that is being used as the
supply tank.  CRITICAL if a lift/boost pump is being used to feed the
header/surge tank.

Yeah, ... Yeah, ...  I know, ... I know, ... some of you will say that you
do it differently and it works for you. Jolly good! I'm really happy for
you.  However,  all of the above has all been figured out in long
distance/endurance rally/off road racing cars with multiple tanks many years
ago.  So please guys,  don't go and try to re-invent settled technology -
you
will only cause yourelves heartache,  and it's all liable to end in tears.

Cheers,

Leon




----- Original Message ----- From: "Paul" <sqpilot@bellsouth.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Saturday, February 12, 2005 6:39 AM
Subject: [FlyRotary] Re: Vapor lock

----- Original Message ----- From: "Ernest Christley" <echristl@cisco.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Friday, February 11, 2005 12:24 PM
Subject: [FlyRotary] Vapor lock


> I'm not sure that I understand vapor lock completely.  Is the problem
> that the fuel gets hot, or that the fuel boils and then the pumps no
> longer work?
>
> I have a plan for a stone cold simple fuel system.  With only one tank
> positioned high, I plan to put both fuel pumps directly under the tank
> which is located behind the cabin (tractor configuration).  Position > the
> fuel regulator beside the pump, and I will only having a single line
> running out to the engine compartment.  Think of it as one LONG header.
> The issue will be that the fuel will not 'circulate'.  What goes out to
> the header at the engine will stay there till it gets used.
>
> Is this a prescription for 'vapor lock', or will any boiling fuel > simply
> get blown through the injectors?
>
Hi, Ernest....I might have it wrong, but I seem to recall that I was told

to

put the fuel pressure regulator just AFTER the injectors/fuel rail. That's
what I did...maybe that's part of my problem?  Paul Conner


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