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One option, with the plumbing you and Rusty are trying, is to make the junction of the high pressure pump and the low pressure feed pump in a manner similiar to a 'water jet pump' or an 'aspirator' that uses a flowing liquid to pump another liquid or gas. Then the fact that the EFI pump is flowing hard becomes an advantage, helping the facet pump when it is turned on.
Word picture:
Envision a "T" fitting with the straight through section going from left to right, the T portion hanging down. Fuel from the EFI pump enters from the left, and exits on the right, going back to the feed tank. Fuel from the Facet pump feeds into the arm of the T.
Modify the "T" fitting so that a slightly smaller tube that is inserted in the inlet side extends partway across the entry point of the arm. Now when fuel flows, a lower pressure point is generated at the exit of this smaller tube, that tends to pull fuel into the stream from the arm connection.
I have noticed this effect on just a straight 'unmodified' T, modifying it is truly 'experimental', but aspirators and jet pumps have a long history of working.
Bill Schertz
KIS Cruiser # 4045
----- Original Message ----- From: <ronmilligan@cox.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Monday, May 30, 2005 11:30 AM
Subject: [FlyRotary] Re: will EFI pumps pump air
Rusty,
I copied your system in doing mine. I asked about the facet over coming the pressure from the returning fuel line. I wish you would have tested yours more before I finished mine. Would it be possible to put a larger diameter return line from where the facet pump line joins the return line? I'm a long way from testing mine so when you find a solution let us know.
Ron Milligan
RV7 QB FUSE
Aliso Viejo CA (Temp: Balad, Iraq)
From: "Russell Duffy" <13brv3@bellsouth.net>
Date: 2005/05/30 Mon AM 11:51:53 EDT
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: [FlyRotary] Re: will EFI pumps pump air
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
Homepage: http://www.flyrotary.com/
Archive: http://lancaironline.net/lists/flyrotary/List.html
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