I threw this together, it
includes some assumptions, but I think it's pretty close to reality. I strongly
suspect 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, that air is displaced automatically and there is no
value to the bleed system. I tested my plane and it definitely self primes. The
Egg crash plane would not pump fuel hours after the vapor lock. 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>
>