Here is a copy of an email conversation with the late Paul Conner, concerning
fuel system return design. 

George Graham <rx7ez@yahoo.com> wrote:

Date: Fri, 25 Feb 2005 13:18:58 -0800 (PST)
From: George Graham <rx7ez@yahoo.com>
Subject: Re: power loss
To: Paul <sqpilot@bellsouth.net>


--- Paul wrote:
> My EFI fuel return goes directly back into the small
> aluminum sump
> tank, which is mounted on the cool side of the firewall,
> behind the rear
> seats. It is always cool to the touch, even when intentionally
> inducing vapor lock shutdown.

Paul, I am concerned that your fuel system design is dangerous.
Hell, we both know that it is, it already has failed you
inflight. If I may be so forward:

The refrigeration cycle is to pressurize a liquid, which creates
heat, lose some heat through a condenser, then drop the pressure
though an orifice. The liquid turns into a cool gas, which goes
into a condenser and picks up heat, then is sucked into the
compressor pump.

Your gasoline is pressurized by the constant volume fuel pump,
then the pressure drops at the pressure regulator, the cool
gas bubbles are returned to the sump, where the pump tries
to suck it again. Vapor lock, can only occur on the low
pressure side of the pump.

The other likely problem is that the gasoline is not required
to flow into the sump tank. The tank is vented into the
strake tank, so that the pump can suck the sump dry, and maybe
some fuel will gravity flow into the sump, maybe not.

I cannot think of a worse setup, and you should change it.

If you stay with the EFI, then you should return the excess
fuel into the tank selected, not a sump tank. Andair makes
such a valve, and JC Whitney has a nice $63.00 electric
tank selector with 3/8 " fittings. I am aware that yours is
\similar to Ed Anderson's design, and he has ignored my advice,
as you certainly may as well.

My carb works good, but is hard to cowl cleanly. I will change
it to either a HA-6A, helicopter horizontal carb, or better yet,
an Ellison someday. After seeing John Slades mixture problems,
I'm not tempted to go that route anymore.

I hope that you are not offended by unsolicited advice, perhaps
I am missing something important. I've been wrong before :)






=====
George Graham
Mazda Rx7ez N4449E
Homepage



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