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Russell Duffy wrote:
Will the EFI pump move enough air through it to disturb the fuel rail pressure that's being delivered from the other pump, I would say yes
I'd bet that you have a 50-50 chance of being right :-) Seriously, I'm not so sure it would pump air well enough to overcome the 43 psi of pressure that the other pump is putting in the rail. I guess the only way to find out it to do the experiment. I'm not completely sure that's what I want to do anyway. Yep, still trying to figure out how to fix my fuel transfer system. What's it look like now?
Remember the recent caution about copying a system 100%, or it becomes a new system? Well, guilty as charged. My system is just like Tracy's, except that I only have one return line to my feed tank. I plumbed the wimpy facet transfer pump into the same line that returns from the regulator. That means the facet pump is trying to push against the return flow from the regulator, and it's not doing too well. Even at it's best, on the ground, with no other pumps on, the facet is slow. In the air, fighting against one EFI pump's return flow, it takes a long long time to see fuel moving. With both EFI pumps on, I almost wonder if fuel isn't going backwards into the non-feed tank anytime the facet wasn't on because the check ball isn't perfect. I added a one way valve to stop this, and to stop the fuel from leveling itself between tanks when parked. The obvious solution is to "simply" (NOT) add another hose to the feed tank. Even if I go through all that hassle, I'm still stuck with the slow rate of transfer of the facet. It's probably still the best option, but I'm going to investigate every other option before doing this. Rusty
One thing I'm considering is to just use the regular pumps to transfer fuel. If you plumb the tanks to a fuel selector, then when you select the aux side the excess flow will end up in what's now your primary tank. This is how some injected Continental engines are plumbed in certified a/c. Not my favorite idea, but it does minimize the changes from Van's stock system. I've got 2 additional tanks to deal with, so I'll have to have a selector somewhere in the system anyway.
If you want to retain the Facet transfer pump system, have you considered trying to make a return fitting on your primary tank configured like a 'jet pump'? If you feed the engine return in one side of the T & the Facet into the bottom, it just might help the Facet instead of hurting it. If you can build a plumber's nightmare with the return line being a smaller diameter & extending slightly past the intersection, it just might work.
I've seen the 1st idea work in certified planes; the 2nd idea is wild speculation.
Charlie
(Wish you could have made it up here this weekend; if you get bored & need a place to fly come on up for lunch sometime.)
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