REFLECTOR:Low fuel light

Sun, 27 Jul 2003 21:17:41 -0500

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Ronnie,
Thanks much.  .72 psig doesn't sound too high.  I'm thinking of blocking
off the vent line and allowing the two over flow vents to pressurize the
3 tanks.  I could also block off one of the over flow vents, but I think
the tank  pressure would get quite unbalanced during climb or descent
because the tank with the vent would change pressure first.  I think a
single vent would work if it were teed between the two tanks AND the
sump was vented to the tanks and not to the vent, but I prefer not to
tackle that plumbing change if the two vents work acceptably.

John

Ronnie Brown wrote:

>  John, I don't have a data point for 150 knots but 174 knots = 20.04
> inches of water or 0.72 psig. I would be concerned about the two
> different over flow vents being at the same static pressure as the
> vent system.  It is difficult to get a good, reliable, accurate static
> pressure at 150 or 200 knots, so you have a good chance of having just
> an inch or two difference between the 3  vents you have, which CAN
> cause flow problems between the three tanks, especially if the central
> vent system is made up of 1/4" lines as many Velocities have. By the
> way, late model Cessnas only have a single forward facing vent,
> because the earlier Cessnas had separate tank vents and fuel levels
> would not stay the same.  The single vent is tied to both tanks and
> there are also one way check valves involved. Ronnie

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Ronnie,
 Thanks much.&nbsp; .72 psig doesn't sound too high.&nbsp; I'm thinking
of blocking off the vent line and allowing the two over flow vents to pressurize
the 3 tanks.&nbsp; I could also block off one of the over flow vents, but
I think the tank&nbsp; pressure would get quite unbalanced during climb
or descent because the tank with the vent would change pressure first.&nbsp;
I think a single vent would work if it were teed between the two tanks
AND the sump was vented to the tanks and not to the vent, but I prefer
not to tackle that plumbing change if the two vents work acceptably.
John
Ronnie Brown wrote:
<blockquote TYPE=CITE>&nbsp;John,&nbsp;I
don't have a data point for 150 knots but 174 knots = 20.04 inches of water
or 0.72 psig.&nbsp;I would be concerned about the
two different over flow vents being at the same static pressure as the
vent system.&nbsp; It is difficult to get a good, reliable, accurate static
pressure at 150 or 200 knots, so you have a good chance of having just
an inch or two difference between the 3&nbsp; vents you have, which CAN
cause flow problems between the three tanks, especially if the central
vent system is made up of 1/4" lines as many Velocities have.&nbsp;By
the way, late model Cessnas only have a single forward facing vent, because
the earlier Cessnas had separate tank vents and fuel levels would not stay
the same.&nbsp; The single vent is tied to both tanks and there are also
one way check valves involved.&nbsp;Ronnie</blockquote>

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