Chris,

I copied the Eggenfelner design on the bypass restrictor circuit for my efi system.  The bleed circuit was their fix for a problem which was discovered after a couple of emergency dead stick landings.  It was caused by air trapped in the fuel delivery system.  Air could get into the lines when a tank was run dry and the pump got a big gulp of air.  Since EFI pumps don't suck very well, they couldn't reprime because of the big air bubble surrounding the pump.  The pump will produce very low pressure in this scenario, enough to force the air through the orifice.  The orifice provides an escape for the air to be bled off which then allows the fuel pump to re-prime itself.  Once the pump re-primes, any remaining air will be purged through the fuel rails and back to the tank through the return system.  Prior to adding the orifice, a large gulp of air would require that one of the lines downstream of the pump to be cracked to bleed off the air.  The orifice isn't big enough to make any significant difference during normal operations.  Yes, the bleed circuit bypasses the pressure regulator.  The same thing could be accomplished by a manually operated solenoid, but that is more complexity.  IMHO, the orifice is a very elegant solution.  Another solution is to never run a tank dry.  ;-)
 

Mark S.

 

On 3/14/07, Christopher Barber <CBarber@texasattorney.net> wrote:

I have the Mistral intake and am setting up my fuel lines.  The lines go into the fuel rail through a big hole (3/8?), but exit through a very tine "pin hole" on the other end.  I am not versed in fuel injection as my history is with carbs in my ol' 65 Mustang ragtop.

 

During the first incarnation my build buddy David had a pressure regulator installed before the fuel rail.  Then, following some internet research on fuel injection by me, I found several sources that stated the pressure regulator is usually installed downstream of the rail.  David figured this may make sense, but felt it should be T'ed back to the sump tank (sump per Velocity plans). 

 

I looked at my friends RV-7 who is installing an Eggennfelder Subaru which also has  pin hole restrictor and tried to copy its pressure regulator set up, however, Dave and my mechanical engineering hangar mate, Richard, do not think it is proper.  I too wondered what the pressure regulator was actually doing since it is downstream of the pin hole which provides a lot of restriction and it was T'ed in a manner that went around the regulator and since the fuel would go by the path of least resistance would in all likelihood bypass the fuel pressure regulator almost completely.

 

I had another engineering friend look at the set up (who btw has worked with some of the Mistral folks as he is heavily involved in the aviation community...the company he owns provides aircraft A/C systems for companies like Cirrus, Moony, Eclipse, Columbia and in the last couple of months he has been in discussions with Cessna, Piper and Honda Jet.....pretty good credentials....and he is the builder of the RV-7 with the Eggenfeilder)  He believes that the Mistral Intake does not need the pressure regulator since the pin hole is doing the job of keeping the rail "charged".

 

We have emailed the contacts at Mistral who have not as of yet responded....it has been a couple of weeks.  I understand they cannot provide major tech support, but I would love some direction.  We hope to be great ambassadors for their product.  I would assume some basic tech info is available.

 

However, since I have yet to hear from Mistral, do any of y'all have any insight and/or solutions as to what would be "best" <g>. 

 

Thanks, I am quite close to first start, but I obviously need to resolve this question.

 

All the best,

 

Chris Barber

Houston, Texas

 

www.LoneStarVelocity.com