I threw this together, it includes some assumptions, but I think it's pretty close to reality. I strongly suspect what part of the FEMA process is that? that the Egg fuel bleed system actually drops the outlet pressure enough that the pump is able to move the small bubble of air at the pump inlet. If you have a well designed system, what exactly would that look like (or NOT look like) that air is displaced automatically and there is no value to the bleed system. I tested my plane and it definitely self primes. How exactly did you do that? Which failure modes and what possible situations did you test for? The Egg crash plane would not pump fuel hours after the vapor lock. Why exactly? Are we sure they actually got to the bottom of it all? It was not a self priming fuel design.

Back to lurking, this my quota of posts for week. ;-)

-al wick

Subject:

Fuel system validation….self priming pump.

Scope:

This procedure is utilized to determine if your fuel system is able to self prime. It applies to EFI high pressure fuel systems.

General:

Self priming fuel systems are lower risk that those that don't. These systems have the ability to resume pumping immediately after a flow interruption. Such as when the pilot runs one tank dry, or if there is vapor lock.

All systems that allow the fuel pump inlet to get wet after a flow interruption are self priming. This condition is vital on high pressure fuel systems, as the pumps are unable to displace air due to the high pressure on the outlet side of the pump. Only when the inlet is wet are the pumps able to resume flow.

Procedure:

Drain all fuel from your tank.

Verify your engine fuel pressure is at normal pressure, this is typically 36 psi for EFI systems.

Activate fuel pump for a few moments to purge fuel from the fuel inlet. You should hear a rattling sound when inlet is purged of fuel. Use care, running pump dry too long can damage pump.

Add fuel to tank.

Activate fuel pump for a few moments until normal pressure is achieved.

Conclusion:

If unable to achieve full pressure in 10 seconds, you have failed the test. Modify your fuel system to self wet the fuel inlet.

On Wed, 15 Jun 2005 09:13:12 -0500 "Mark R Steitle" <mark.steitle@austin.utexas.edu> writes:
> Jofar,
> The real purpose of the bleed circuit is to allow the pump to
> reprime
> itself. Once that happens, the pump builds up pressure again, and
> forces all the remaining air out through the pressure regulator.
> With a
> 5-gal tank sitting on the floor, my system (running one pump) can
> reprime itself in about 10 seconds. Yes, under the right
> circumstances,
> that could be the longest 10 seconds of my life. This should only
> happen if you run a tank dry. But if that happens, the procedure
> will
> be to switch to the other tank (should have fuel), then turn on the
> boost pump. That should reduce the recovery time to something less
> than
> 10 seconds.
>
> Mark
>
> -----Original Message-----
> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
> On
> Behalf Of jesse farr
> Sent: Wednesday, June 15, 2005 8:47 AM
> To: Rotary motors in aircraft
> Subject: [FlyRotary] Re: Engine Not Starting
>
> I don't know nothing (actually pretty much anything) about any of
> this
> but
> that has never stopped me from having and voicing an opinion; so, if
>
> injectors only fire small percentage of time and fuel & compressed
> air
> flow
> not sufficient at times to clear out in time to get started while
> flying
> ac,
> bleed return definitly sounds like good idea. But, if sufficiently
> far
> away
> from injectors, then even though now have flow established to the
> bleed
> point, you will still have slow go to purge remaining compressed
> air,
> vapor
> and allow fuel to actually flow from there to injectors and inject.
> It
> may
> just take a few seconds longer but that is still a tight a-- time
> of
> flying,
> starting, praying, cursing own stupidity, etc.. Could I suggest
> might be
>
> better to put bleed point at end of fuel rail so as to pass vapor
> all
> the
> way more quickly ? After all, small orfice and line return to tank
> shouldn't
> create that much more of a problem. Is there some other problem
> there
> that I
> simply do not know enough to understand ?
> jofarr, soddy tn
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
>
>

-al wick
Artificial intelligence in cockpit, Cozy IV powered by stock Subaru 2.5
N9032U 200+ hours on engine/airframe from Portland, Oregon
Prop construct, Subaru install, Risk assessment, Glass panel design info:
http://www.maddyhome.com/canardpages/pages/alwick/index.html