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Jesse,
My notion of a bleed circuit is to purge air downstream of the pump so it will be able to self prime (like, it can't if it's trying to pump enough air to open the regulator bypass). I'll put it at the high point prior to the rail to get the best shot at air and vapor. Additionally, anything that boils in the rail after shutdown will be vented through the bypass circuit. Once running, trapped air downstream of the injectors should flow fairly quickly through the rail and be vented to the tank by the regulator. I guess that indicates that the rail should be above the injectors so the air can pass over the injector connection in the rail while fuel goes to the injector. This last may not be too important, but if it's easy to implement, why not ...
Covers all the bases I can see ... Jim S.
jesse farr wrote:
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
----- Original Message ----- From: "Mark R Steitle" <mark.steitle@austin.utexas.edu>
My bleed circuit is about midway up on the firewall, and definitely not
at the highest point in the system. I'm not convinced that it needs to
be at the highest point. The reason is that if you have an airlock,
preventing the pump from priming, the engine won't be running at that
time. As soon as the pump is able to re-prime, it will start flowing
30+ gpm of fuel. If you're returning fuel back to the tank, the air
will be forced out of the fuel rail and back to the tank, and you're
back in business.
This is a bit different approach from what Leon posted, so there may be
some merit to having the bleed at the highest point. It certainly
wouldn't hurt any, but I have had positive results with my system and
placing it near the pressure regulator made the plumbing simpler.
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