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To: flyrotary@lancaironline.net
Date: Tue, 14 Jun 2005 12:51:30 -0400
Subject: Re: [FlyRotary] Re: fuel pump mounting ( fuel system architecture)
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From: WALTER B KERR <jbker@juno.com>


On Tue, 14 Jun 2005 09:29:39 -0400 "John Slade" <sladerj@bellsouth.net>
writes:

> > Does the pump have any suction on the inlet?
> I did an experiment with the pump on a 4 foot bench, and a gas can 
> on the
> floor. The pump primed itself with no difficulty. Having said that, 
> a
> scenario like this in a plane would be just asking for vapor lock.
> 
-----------------------------------------------

Hi John, I like your test but do not understand your conclusion. If the
pump will prime with a 4 foot negative head that sounds good to me. You
may form some vapor in the system but if the pump can lift 3 feet plus of
fuel with air in the pump, that says to that it will pump the fuel thru
the system and the regulator will return the vapor or air back to the
tank or the sump depending on how it is plumbed with a regulator and
return system.

My current system does not have a sump. It is a low wing configuration
(RV9A) and the fuel comes out of the tank to the selector valve to a
Facet boost pump and up to the parallel walbro pumps (GSL393) that are
maybe 12 inches higher than the tanks. Then to the injectors and
regulator and  back to the tank. I have never had to use the boost and
considered removing it earlier, but decided to leave it in case the
walbro's may not prime in some situation. When I run the pumps a short
time after shutdown you can here bubbles returning to the tank
momentarily and then clearing after maybe 3-5 seconds. 

My basis for this is basically what the Otter does except he only pumps
and return fuel to the left tank.This system definitely is superior to a
non bypass system such as carb, etc since the fuel at the pumps will
always be close to ambient temp. I only return fuel to one tank(the right
one since I sit on left) and when I wish to get fuel out of another tank,
the bypass fuel returns the fuel back to right tank. This may require
some pilot effort, but fiqured if one of the pumps is operable I can use
all of the fuel on board.  Vans float gage that are taylored to a
specific model are really accurate. The downside of this system is
failure of the supply from the right tank due to clogging etc.Everything
is a compromise and one just has to do what they are comfortable with
after reveiwing as many sucessful systems as possible.

Bernie, 40 hours and holding on 9A 13B