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Date: Wed, 17 Aug 2011 11:22:14 -0400
From: Ernest Christley <echristley@att.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: Dennis Haverlah Fuel System...or any others,
 for that matter.
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Al Wick wrote:
> I'm really concerned for some of these fuel designs. The fuel bleed has 
> nothing to do with vapor lock. Virtually no effect at all.
>  

I don't know why others are doing it, but for me, the bleed has nothing at all to do with vapor lock.  Some 
conversations have been mixed together, so I can see how that could be the impression.  The point of the pressure bleed 
is to bleed off the pressure after shutdown.

I have a strong, positive head pressure going into my pumps.  They, and the regulator, are about 8" directly below the 
tank.  Excess fuel goes back to the opposite side of the tank from the pickup, and a single line goes forward to feed 
the injectors.  The fuel lines are arranged such that heat soaking the lines to the point of boiling the gas will push 
liquid fuel down hill and behind the firewall, isolating the gaseous gas with its heat at the top of the line.  Turning 
the pumps on will pressurize the line to 55psi, returning most of the gaseous fuel back to a liquid state.  The ECM is 
programmed for a longer clearing pulse on hot start.

The point of the bleed is to allow fuel to move back to the tank.  I had the issue of a the pressurized lines being 
perfectly sealed.  The pressurized fuel was finding the path of least resistance out, which just happened to be out the 
injector and into the intake manifold where it sat as a little puddle.  Heat soaking the lines would not push liquid 
fuel downhill and back behind the firewall.  It would push more fuel into the manifold.  A puddle of gas sitting in a 
composite manifold, just above a hot exhaust stack is just bad mojo.  A poorly sealed regulator allows the pressure to 
bleed off in about 5 seconds (give or take), isolating the hot fuel in front of the firewall, and keeping the rest cool 
and out of the intake manifold.

Got nuthin' to do with vapor lock.