Fuel Tank Leak Testing
Posted: Fri Feb 17, 2012 8:34 pm
Hi to all you builders who are ready to test the fuel tank. If you use
the glove method, or the safe glove method, you may miss a significant
leak. Here is the method I used, after doing some calcs and many tries.
A long length of tubing can be attached to the top tank fitting, (the
cross vent or the top of the sight gauge) and drooped to get a U-tube
pressure gauge. Put a tee with a valve next to the tank for applying
pressure, by blowing into the tank. Support the tube so that you can
put about 2 feet of water in the tube without danger of it entering the
tank, (You would have to dry it out after the test) and mark the zero
position, or tape it to a scale. Seal the filler hole. It's side vent
(if you have one) can be sealed with a thick rubber band from the
kitchen. A glove over the neck is not too good because you can't get
enough pressure I feel. (I used the gasket from the tank cap, smear with
grease and with a flat plate and a weight on it, a block of steel,
(bucking bar))
The test. Blow into the tank through the valved tee connection to get
about 12" water pressure. Close the valve and let it settle (a couple
of minutes anyway) then mark the water levels, note the time, and the
temperature. You may have a big leak showing, so check all your tubing
connections and valves. Leak check soap solution may be useful now.
When you think there is no leak showing, let it stand overnight at
least.
The results.
A pressure change of 1" water is equivalent to 250 ml volume.
A temperature change of 1 deg.C is equivalent to 300 ml.
(The above based on 90 liters tank vol, and 27 deg C)
So in the morning you know the total leakage within 400 ml. If the tank
has been pressurized for a significant time then any leak will be dry,
and the leakage will be air.
How tight is tight? One drop per min. will give a big stain. One drop
per hour is probably not noticeable. These become fluid leaks of 5 ml/hr
and 0.1 ml/hr respectively. And that equates to 125 and 2.5 ml/hr air
respectively (a la Bernoulli). So your target is set between these, say
15 ml/hr air.
Overnight 16 hrs at 15 ml/hr sets the target at 240 ml total. So you
have to know the temp to less than 1 deg, or wait another day.
Glove tests? Tell you a little bit. If you have a big small leak
(contradiction in terms eh?)(500 to 5000 ml/hr) the glove will stay up
till you leave the shop. Then when it cools the pressure drops to BELOW
atmos. The leak is INTO the tank. When you get back and raise the temp
1/2 deg, the glove refils and "Hurray, it doesn't leak" Oh yeh?
Another note: when you fill the tank by blowing into it, you put warm
air in, (37 deg C) This air then cools in a matter of a couple of
minutes, giving a leak indication. WORRY!!! It took me a while to
realize what was happening, and so the reason to wait till it stabilizes
before you start the timed test.
What pressure to use? Max height of fuel is about 8", and max g of 5
gives 40" fuel as max pressure. This is eqivalent to 27" water max
design pressure. So using 12" water = 18" fuel looks OK and gives
enough to cause a leak if one is there.
Hope this helps somebody, and doesn't worry you guys that used the safe
test. You will know if you have a significant FUEL leak soon
enough!!! (:((
Phil Stubley, R302.
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the glove method, or the safe glove method, you may miss a significant
leak. Here is the method I used, after doing some calcs and many tries.
A long length of tubing can be attached to the top tank fitting, (the
cross vent or the top of the sight gauge) and drooped to get a U-tube
pressure gauge. Put a tee with a valve next to the tank for applying
pressure, by blowing into the tank. Support the tube so that you can
put about 2 feet of water in the tube without danger of it entering the
tank, (You would have to dry it out after the test) and mark the zero
position, or tape it to a scale. Seal the filler hole. It's side vent
(if you have one) can be sealed with a thick rubber band from the
kitchen. A glove over the neck is not too good because you can't get
enough pressure I feel. (I used the gasket from the tank cap, smear with
grease and with a flat plate and a weight on it, a block of steel,
(bucking bar))
The test. Blow into the tank through the valved tee connection to get
about 12" water pressure. Close the valve and let it settle (a couple
of minutes anyway) then mark the water levels, note the time, and the
temperature. You may have a big leak showing, so check all your tubing
connections and valves. Leak check soap solution may be useful now.
When you think there is no leak showing, let it stand overnight at
least.
The results.
A pressure change of 1" water is equivalent to 250 ml volume.
A temperature change of 1 deg.C is equivalent to 300 ml.
(The above based on 90 liters tank vol, and 27 deg C)
So in the morning you know the total leakage within 400 ml. If the tank
has been pressurized for a significant time then any leak will be dry,
and the leakage will be air.
How tight is tight? One drop per min. will give a big stain. One drop
per hour is probably not noticeable. These become fluid leaks of 5 ml/hr
and 0.1 ml/hr respectively. And that equates to 125 and 2.5 ml/hr air
respectively (a la Bernoulli). So your target is set between these, say
15 ml/hr air.
Overnight 16 hrs at 15 ml/hr sets the target at 240 ml total. So you
have to know the temp to less than 1 deg, or wait another day.
Glove tests? Tell you a little bit. If you have a big small leak
(contradiction in terms eh?)(500 to 5000 ml/hr) the glove will stay up
till you leave the shop. Then when it cools the pressure drops to BELOW
atmos. The leak is INTO the tank. When you get back and raise the temp
1/2 deg, the glove refils and "Hurray, it doesn't leak" Oh yeh?
Another note: when you fill the tank by blowing into it, you put warm
air in, (37 deg C) This air then cools in a matter of a couple of
minutes, giving a leak indication. WORRY!!! It took me a while to
realize what was happening, and so the reason to wait till it stabilizes
before you start the timed test.
What pressure to use? Max height of fuel is about 8", and max g of 5
gives 40" fuel as max pressure. This is eqivalent to 27" water max
design pressure. So using 12" water = 18" fuel looks OK and gives
enough to cause a leak if one is there.
Hope this helps somebody, and doesn't worry you guys that used the safe
test. You will know if you have a significant FUEL leak soon
enough!!! (:((
Phil Stubley, R302.
*-----------------------------------------------------------------------------------*
Contributors' page at:
http://www.dcsol.com/murphy-rebel/contributors.htm
Visit the book store at:
http://www.dcsol.com/murphy-rebel/book_store.htm
Archives located at:
http://www.dcsol.com/murphy-rebel/lists/default.htm
*-----------------------------------------------------------------------------------*
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