Manometer Testing of Fuel Tanks

[g zero]

I tested my tanks side by side with two manometers , watched them both go up and down with temp and pressure change for a week ,they stayed level with each other the entire time .

[snopercod]

Originally Posted by az_gila

..can also affect the manometer levels.

Those both need to be accounted for and, be warned: If you pressurize the tank when it's cold outside and then it warms up a lot, there is a real danger that you can overpressurize your tank. The only thing that saved me was that the open end of the manometer was low enough that the water spilled out when the pressure in the tank got too high. So when you run this test, make sure the open end of your manometer is no higher than the maximum pressure your tank can withstand.

[snopercod]

You can account for temp/press factors yourself using the formula P1/T1 = P2/T2 where P and T are both in Absolute units. (The "V" term drops out because the Volume stays constant.) Add 459.67 degs to convert the Fahrenheit temp to absolute temperature and add the barometric pressure to the manometer reading (converted to Inches Hg) to get the absolute pressure inside the tank. Be sure to use the barometric pressure rather than the "altimeter setting". Conversion factors: 1" Hg = 13.6" H20. 1 PSI = 27.68 "H20.

Let's say you pressurized your tank to 13.6" H20 differential on the manometer (which is roughly 1/2 PSI). If the reported altimeter setting at your airport was 29.92" and your airport was at 1,000' elevation, then the barometric pressure would be ~28.92" Hg. (using the approximate 1,000' elev. = 1" Hg. conversion factor). The absolute pressure in the tank would then be 28.92 + 1 (13.6? H2O/13.6) or 29.92" Hg. If, during the test, the outside barometric pressure dropped to 28.00, and since the number of molecules in the tank remains constant (assuming no leaks), the weight of water in the manometer column would have to increase to hold a constant 29.92? to satisfy the equation. Thus the water in the column would rise to 26.11? H20 differential (1.92? Hg x 13.6) to make up for the decreased barometric pressure holding the air the tank. This all assumes there were no leaks and the temperature stayed the same.

So you definitely want to pressure test your tank when the barometric pressure isn?t changing rapidly.

Disclaimer: My coffee hasn't kicked in yet so please check my math and methodology before using any of this.

[JimWoo50]

Pour about a gallon and a half fuel in it. You can leave tank baffle side down and fuel will cover the source of most leaks. Leave in garage or outside over night. If there's a leak you will see or feel it. You can stand tank on either end too. May not require a whole gallon and a half just enough to submerge the large seams by the baffle.