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Thanks Marv.
I'm a little slow this morning, but I see what you mean.
The wings are mounted high on MGDQ. I'm running a -6 line from each to a
1/2 T, to a gascolator, two series mounted fuel filters and pumps, to -6
line to feed rail. A -6 line from the regulator back to a T that feeds both
tanks. The andair valve isn't used in my install. Each tank has a separate
valve for feed and return. I plan on leaving both return lines open. The
initial plan is to be able to fly with both tank feed and return valves open
and don't have to worry about anything. Of course, reality will take care of
this theory. This also allows me the option of returning the fuel to one
tank if I should ever get really low on fuel.
The only problems that this creates right now is that the return line may
overflow one tank if not being watched. The other is accidentally turning
off both return lines. Didn't have room for the Andair valve. My rudder and
elevator controls, amphib aux pump, and assorted float hoses and wiring,
took up that space.
Barny
MGDQ 20bt (flying to Iola for lunch today in C 150)
----- Original Message -----
From: Marvin Kaye <marv@lancaironline.net>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Friday, November 12, 2004 8:18 AM
Subject: [FlyRotary] Re: EFI stuff
> The "check" valves you mentioned aren't actually check valves. Check
valves
> have a very low cracking pressure (0.5-2psi) and are intended to basically
> free flow in one direction and block flow in the other. These valves are
> called secondary bypass valves and they open at 50psi, just a bit higher
than
> our regulated pressure. They serve several purposes... first, without
them
> when it's time to switch tanks and you turn on the pump you'll be
switching
> to, that pump's full pressure is dead-heading against the body of the
selector
> valve, not good for the pump, and if you don't switch immediately you'll
blow
> the breaker (don't ask me how I know). Second, hi-pres pumps don't
typically
> have an internal bypass, so the pump's full pressure pushing on the body
of
> the selector valve makes it very difficult to switch tanks for anyone with
> less-than Popeye arms. Third, the pressure buildup against the valve
without
> them causes a sudden spike in fuel pressure when the selector is actually
> switched and can cause a very-rich-followed-by-lean condition as the FP
> regulator deals with the spike and then its absence. The whole idea is to
> keep the fuel pressure on both sides of the selector valve within
reasonable
> limits to facilitate the several things I've mentioned above (and probably
> more).
>
> All I can tell you is that I wish I'd put them in in the first place.
>
> <Marv>
>
> "Barnhart" <dsbarno@vbe.com>:
>
> Marv,
>
> What is the function of the check valve between the feed and the return
> line?
>
> I have my return line running straight back to the tanks from the
regulator
> on the fuel rail.
>
> Barny
> MGDQ 20bt
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