joedallas
Well Known Member
Is 60" of water a good test of the fuel tanks
http://www.omega.com/pptst/PGL-25.html
Thanks
Joe Dallas
http://www.omega.com/pptst/PGL-25.html
Thanks
Joe Dallas
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".
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.
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.
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
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.
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).