Fuel tank testing

[Mike Davis]

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Wed, 15 Apr 1998 23:29:58 -0400
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From: "Joel Jacobs" <jj@netexp.net>
To: "rebel builders" <murphy-rebel@dcsol.com>
Subject: Fuel tank testing
Date: Wed, 15 Apr 1998 23:30:20 -0400
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Hi folks,
I see there are a few messages regarding low pressure gauges and fuel tank
testing. I had pretty good luck with a gauge I made and I posted to the
list once about it but it's been a while so here's a repost.

-----Original Message-----
From: Joel Jacobs <jj@netexp.net>
To: Murphy-Rebel@dcsol.com <Murphy-Rebel@dcsol.com>
Date: Friday, September 05, 1997 5:49 AM
Subject: Re: REBEL: Re: Fuel tank testing


My manual said 3lbs but I chickened out at 2lbs after seeing the way the
skins were bulging. I'll describe the pressure guage I used.

The pressure guage is constructed from about 30ft of 5/16 plastic tubing.
The length should be enough to go from the tank to the ceiling then form a
loop down to the floor and back to the ceiling. Put some water in the loop.
It should be about half way between the floor and the ceiling in both sides
of the loop.

Mark both tubes with a marker where the water is. These will be the 0 psi
marks. As you pressurize the tank, the water in one side will rise and the
water in the other side will decrease by the same amount. The DIFFERENCE
between the two is the water column hight.

A gallon of water weighs 8lbs and is 321 cubic inches so 1 pound would be
231/8 or about 29 inches of water column. As you can see a one ounce/sq in.
change will move the water column 1.5 inches so the guage is VERY accurate.

Mark both tubes 14.5 inches above the 0 psi marks, these are the 1 psi
marks. (one side goes up 14.5" and the other side goes down 14.5" for a
difference of 29") Mark both tubes 14.5 inches above the 1 psi marks, these
are the 2 psi marks. By marking both tubes the guage will measure vacume as
well as pressure.

As far as how much to test to, if you think about it, the maximum width of
the wing is 9 inches so at 4 G's the pressure would be the equivilent of 36
inches of fuel. Gas is 6 lbs/gallon so 36" of fuel would be 6/231 X 36 or
about .935 psi so testing to 1.5 or 2 psi should be enough.

My water column guage would go up and down 6 or 8 inches every day due to
temperature changes, but it averaged about 1 psi for a week so I think it'll
be ok.

The tank is not as strong under vacume. I did pull 1psi vacume on mine to
try to suck in some proseal and it didn't collapse.

Joel

P.S. The filler neck was a pain in the neck to get sealed for the test.
Even un-vented caps would leak. I ended up stretching some inner tube
rubber over the neck and wrapping tightly with that waxed tie cord stuff.
So, if you think you have a leak, double check the filler neck seal.







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