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Hi Bill... Welcome back.
The bleed circuit came about as a result of two Eggenfellner Subaru accidents/incidents traced to fuel starvation. They hashed it over on the Subaru group and the simplest solution was to add a bleed circuit between the fuel rail and the return line (bypassing the pressure regulator), allowing any trapped air to be easily forced out of the system. Preventing "weeping" of the injectors was a secondary benefit.
I had experienced a similar problem (on the ground) with my 20B Lancair ES after running the tank dry. The efi pumps refused to reprime the system unless I cracked a line at the fuel rail to let the air escape. Once I did that they would reprime and everything was fine again.
A similar problem happened to another Lancair ES with a certified engine. They purposely ran one tank dry in flight in order to recalibrate the fuel gauge (on the ground). Upon doing so, and switching to the other tank, they couldn't get the fuel pumps to reprime and almost had to do an emergency landing on an interstate in Colorado. Their $600 dual-stage boost pump finally worked and they were able to get it going again and land safely.
I'm not advocating that everyone add this bleed circuit, only that they test to see if their system will reprime if/when a tank is run dry. Once installed there is nothing to mess with or remember to do, and I don't have to worry about spraying fuel when working on the efi system.
Mark S.
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From: Rotary motors in aircraft on behalf of Bill Eslick
Sent: Fri 5/5/2006 6:39 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Fuel system pressure bleed off
Call me crazy, but I have had no trouble with flooding since day one. That is probably because I always shut the engine down by turning off the fuel pump.
The original engine I bought for education was declared inop by its previous owner. Turns out it was only flooded (due to leaky injectors). I read about the problem and the fix like y'all are doing, but killing the pressure at shutdown seemed simpler to me.
--
Bill Eslick
www.weslick.com
On 5/4/06, Mark R Steitle <mark.steitle@austin.utexas.edu> wrote:
Ben,
I tapped the ID of a Tee fitting to accept the motorcycle carb jet. Then I screwed the jet into the threaded hole with some Lock-tite to keep it in place.
Mark
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From: Rotary motors in aircraft [mailto: flyrotary@lancaironline.net] On Behalf Of Ben Schneider
Sent: Wednesday, May 03, 2006 6:23 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Fuel system pressure bleed off
Group...
I am installing my fuel system on my Renesis right now. I seem to remember (correct me if I am wrong) that the consensus was to use a .020 orfice bypass of the regulator to bleed off the pressure in the event of pump prime loss.
My question is, how exactly are some of you going about this? Are you welding an AN fitting shut, then drilling it out to .020? Is there something of this nature commercially available? Suggestions? I have only to run the fuel lines, then wire the engine, a few other little misc. items, and I should be ready for first engine start.
Ben Schneider N713R RV7 Renesis
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