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Fuel tank pressure test

A very simple manometer can be built with a few feet of clear tubing and some colored water. Air the tank untill the water raises 30". This will give approximately 1psi. Spray with soapy water and look for bubbles.
 
I agree with Barney. Gauges are expensive and can be inaccurate or they can break. Manometers are inexpensive to make and are very accurate. Search the web for "Homemade Manometer".
 
Manometer

Mich48041 said:
I agree with Barney. Gauges are expensive and can be inaccurate or they can break. Manometers are inexpensive to make and are very accurate. Search the web for "Homemade Manometer".
Click to expand...

I documented mine. It's on the "Tanks" page of my blog. Scroll to the bottom.
27.7"=1 psi
 
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Joe -

I would suggest not surpassing 1 psi as the instructions suggest. I used an inch meter and took the pressure to 25 inches of water ... which as previously mentioned is just a little under 1 PSI.

At that pressure, the tank was bulging noticeably. After the test the tank returned to normal shape. I would fear that with more pressure and the tank could possibly become barreled and possibly have clearance issues.

Also note, the pressure will vary with air temperatures ... I started my test when it was 78 degrees and it went into the low forties overnight so the gauge was reading quite a bit lower the next morning. I placed the tank in front of a heater to blow some warm air on it and the reading on the gauge instantly began to rise.

Happy Building,
 
I just put a couple of psi on the tank and used SNOOP (soapy water) to check for leaks. I got paranoid when I didn't find any, but after 4 years no fuel leaks.
 
Food for thought for those new to the tank building business. The manometer, or pressure gauge, is NOT the tool you will use to determine whether you have a good seal on your tank or not. As posted above, temperature changes can drastically change the pressure readings, or height of the water. So given this very volatile pressure change due to uncontrollable environmental conditions DO NOT rely on the reading you see as the sole tool for determining if you do, or do not, have a leak. Pressure gauges, manometers, even balloons are secondary tools to determine the pressure you have in the tank. In the case of the balloon, it can also function as a pressure relief valve. However, none of those serves as a tool to determine if you have a quality seal with the tank.

A spray bottle full of soapy water is your tool for determining and/or finding leaks. Use the manometer, pressure gauge, balloon to monitor pressure. Seal off the tank, pressurize it (with 1 psi or less), then get busy with the soapy water spray bottle and spray every conceivable rivet, seam, fitting and observe whether any bubbles develop. Believe me, it will be very obvious if any leaks are present.
 
Steve - agree - -

I spray soapy water the next day after working on a tank. Using the balloon method is fine for low pressure. Spray and spray. Let it set for a while and keep watching. Very tiny bubbles sometimes are harder to see. Once satisfied, wash it down and let it set for a few more days.
 
Yes, the manometer water level will rise and fall with temperature and atmospheric pressure changes. But if the average water level over a long period of time does not change, then there are no leaks. Of course a significant leak will show up immediately.
 
RVbySDI said:
Food for thought for those new to the tank building business. The manometer, or pressure gauge, is NOT the tool you will use to determine whether you have a good seal on your tank or not. As posted above, temperature changes can drastically change the pressure readings, or height of the water. So given this very volatile pressure change due to uncontrollable environmental conditions DO NOT rely on the reading you see as the sole tool for determining if you do, or do not, have a leak. Pressure gauges, manometers, even balloons are secondary tools to determine the pressure you have in the tank. In the case of the balloon, it can also function as a pressure relief valve. However, none of those serves as a tool to determine if you have a quality seal with the tank.

A spray bottle full of soapy water is your tool for determining and/or finding leaks. Use the manometer, pressure gauge, balloon to monitor pressure. Seal off the tank, pressurize it (with 1 psi or less), then get busy with the soapy water spray bottle and spray every conceivable rivet, seam, fitting and observe whether any bubbles develop. Believe me, it will be very obvious if any leaks are present.
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I fully agree (where is the Like/Thumbs up button? ;))
 
Thanks All

Thanks All

I have three tanks in my fuel system,
two 10 gallon tanks in the wings and a 1.9 gallon fuel tank under the baggage floor.

The tanks are smaller and stronger than the RV12 tank.

My shop is always 76 to 77 degrees however I cant control the barometric pressure


I will hand pump the tanks to 40 inches h2o and soap them up to look for leaks.

Then leave them under pressure until the barometric pressure reads the same as the day I pumped them up.

Again
Thanks All

Joe Dallas
 
Confused

Joe
Just thinking about your answer

If the Manometer is of good quality and is accurate to 1%
then it should not make any difference if the atmospheric pressure changes

The atmospheric pressure will act on the meter and tank the same.

Is this not true?

Joe Dallas :confused:



Mich48041 said:
Yes, the manometer water level will rise and fall with temperature and atmospheric pressure changes. But if the average water level over a long period of time does not change, then there are no leaks. Of course a significant leak will show up immediately.
Click to expand...
 
Pressure

joedallas said:
Joe
Just thinking about your answer

If the Manometer is of good quality and is accurate to 1%
then it should not make any difference if the atmospheric pressure changes

The atmospheric pressure will act on the meter and tank the same.

Is this not true?

Joe Dallas :confused:
Click to expand...

It should but maybe we need somone who stayed in a Holiday Inn to do the math.:D
Works for me. Might explain why mine sat in the living room for a month and the only change was minor fluctuations in temp. After a month, I called them good.
 
If the tank is a fixed shape and sealed, then atmospheric pressure can not act upon its contents. Van's tank is semi-ridged. The sides will flex a certain amount. So yes, atmospheric pressure will affect the internal pressure a certain amount. But the tank sides will not flex enough to equalize the inside and outside pressures. This is all theory. In actual practice, differential pressure indicated by a manometer will vary with atmospheric pressure changes.
I have not stayed in a Holiday Inn and have forgotten the math dealing with gas laws that I learned in high school. :D
 
I didn't stay at a Holiday Inn and I'm not smart enough to prove it with math, but I think I have a practical understanding of how a manometer works.

In this instance atmospheric pressure is only influencing one side of the manometer because the other side is connected to the closed fuel tank.

If we assume (rather safe assumption in my opinion) that the fuel tank is rigid enough to not be influenced by the small changes in barometric pressure that can happen with a couple of days of weather change while it is under the approx 1 PSI test pressure, then a change in the baro. value will not be self compensating.

If the baro. goes up it will indicate a very slight leak when there is none.
If the baro. goes down slightly while the tank pressure also goes down slightly because of a very small leak, it can actually falsely indicate no change on the manometer indication even though there is a very small leak present.

It is for this reason that I recommend using a leak indicator solution and not bother with waiting a couple days to see if the manometer changes.
 
Scott
The test that Vans uses for the standard RV12 is fine.

My aircraft has two wing tanks and a header tank that will be tested by the soap and water method prier to installing them.

After I install the total fuel system I will do additional testing before installing the top wing skins.
I like to know how things work ( not assume )

Removing a wing skin to fix a small leak is something I would like to avoid.

My question is what would be the maximum pressure in inches of water that would not be a destructive test ?

My shop is temperature controlled to + or - 1 degree.

The manometer is designed to test the difference between tank pressure and atmospheric pressure.

P gas > P atm = 40 inches of water -- this is the question ?

P gas = tank pressure in inches of water
P atm = atmospheric pressure in inches of water

This would mean that a change in atmospheric pressure will be equal on the outside of the tank and the open side of the manometer.

My View

Joe Dallas





rvbuilder2002 said:
I didn't stay at a Holiday Inn and I'm not smart enough to prove it with math, but I think I have a practical understanding of how a manometer works.

In this instance atmospheric pressure is only influencing one side of the manometer because the other side is connected to the closed fuel tank.

If we assume (rather safe assumption in my opinion) that the fuel tank is rigid enough to not be influenced by the small changes in barometric pressure that can happen with a couple of days of weather change while it is under the approx 1 PSI test pressure, then a change in the baro. value will not be self compensating.

If the baro. goes up it will indicate a very slight leak when there is none.
If the baro. goes down slightly while the tank pressure also goes down slightly because of a very small leak, it can actually falsely indicate no change on the manometer indication even though there is a very small leak present.

It is for this reason that I recommend using a leak indicator solution and not bother with waiting a couple days to see if the manometer changes.
Click to expand...
 
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The highest atmospheric pressure ever recorded is about 32" Hg.
The lowest atmospheric pressure ever recorded is about 26" Hg.
That converts to about 3 psi pressure differential.
But you would have go to the Sahara desert for the high pressure and to the center of a hurricane for the low pressure.
It is not something to be concerned about if using a manometer because the pressure can never exceed the height of the water column. Suppose that you bend 60" of tubing in the shape of the letter "U". Each side of the "U" is about 30" high. You fill the tube half full of water, 15" per side. Connect one end of the tube to the fuel tank and pressurize the tank until the difference in height between the left and right side of the water column is 27" or about 1 psi. It doesn't matter how low the atmospheric pressure becomes because the pressure inside of the tank compared to outside of the tank can never exceed 30" of water, or whatever you put into the tube. You could take the tank with manometer into a vacuum chamber and suck all of the air out and the tank will not be damaged because if the pressure inside of the tank ever exceeds 30" of water, the water and tank air will be blown out of the manometer. So essentially the manometer is a pressure relief valve. The pressure will never exceed the height of the water column.
Since your tanks are cylinders and not cubic shape, they will withstand even more pressure than Van's tanks. There is no concern with damaging them with a manometer filled with 30" of water total (left + right).
 
Home Tanks

Joe
My tanks are homemade.

Wing Tank
A_06_04_04.jpg


Header Tank
A_07_05_09.jpg


http://joesrv12.com/Builder Log/al_06_05.htm

Joe Dallas


Mich48041 said:
The highest atmospheric pressure ever recorded is about 32" Hg.
The lowest atmospheric pressure ever recorded is about 26" Hg.
That converts to about 3 psi pressure differential.
But you would have go to the Sahara desert for the high pressure and to the center of a hurricane for the low pressure.
It is not something to be concerned about if using a manometer because the pressure can never exceed the height of the water column. Suppose that you bend 60" of tubing in the shape of the letter "U". Each side of the "U" is about 30" high. You fill the tube half full of water, 15" per side. Connect one end of the tube to the fuel tank and pressurize the tank until the difference in height between the left and right side of the water column is 27" or about 1 psi. It doesn't matter how low the atmospheric pressure becomes because the pressure inside of the tank compared to outside of the tank can never exceed 30" of water, or whatever you put into the tube. You could take the tank with manometer into a vacuum chamber and suck all of the air out and the tank will not be damaged because if the pressure inside of the tank ever exceeds 30" of water, the water and tank air will be blown out of the manometer. So essentially the manometer is a pressure relief valve. The pressure will never exceed the height of the water column.
Since your tanks are cylinders and not cubic shape, they will withstand even more pressure than Van's tanks. There is no concern with damaging them with a manometer filled with 30" of water total (left + right).
Click to expand...
 
They do not look homemade. Good work.
Here is an idea. Lay a straight edge on the tank and slowly pressurize the tank. Light appearing under the straight edge will indicate bowing. Stop increasing pressure at that point.
 
I'd be more worried about temperature fluctuation in a long running test. I liked the SNOOP method because all a manometer tells you is that you have a leak SNOOP tells you the location if there is one.
 
I didn't stay at the Holiday Inn either, but I went to the plumbing department at Home Depot and bought a bottle of leak detecting spray. Not sure how it compares to snoop, but supposedly better than dishwashing soap and water.
 
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