I began pressure testing my pre-built fuel tank today. I used Van's fuel tank test kit, manometer method. I pressurized the tank as per Vans instructions (just over 5' separation on the manometer). I left it to sit for a while. Over about 6 hours the tank lost about 3 or 4 inches (on the manometer) of pressure. I sprayed soapy water and found the fuel cap to be leaking. I so I put some plastic food-wrap around the inside of teh fuel cap, and then put tonnes of duct tape all over the cap. I re-pressurized, but still getting a leak through the cap (through all the duct tape).
I proceeded to check for other leaks by spraying soapy water over all the rivet lines and other fittings/joints. There was no other obvious bubbling.
I know one builder who bought a special plug for the fuel cap opening (expandable rubber plug), and he used that to hold the pressure and then let the pressurized tank sit for a few days to check for slow leaks.
1) Just wondering what others have done? Soapy-water test only, or seal it up the fuel cap somehow and let it sit for a few days to watch for pressure changes?
2) is it normal to notice some bulging of the skins between the ribs on the bottom of the tank, when it is pressurized?
I proceeded to check for other leaks by spraying soapy water over all the rivet lines and other fittings/joints. There was no other obvious bubbling.
I know one builder who bought a special plug for the fuel cap opening (expandable rubber plug), and he used that to hold the pressure and then let the pressurized tank sit for a few days to check for slow leaks.
1) Just wondering what others have done? Soapy-water test only, or seal it up the fuel cap somehow and let it sit for a few days to watch for pressure changes?
2) is it normal to notice some bulging of the skins between the ribs on the bottom of the tank, when it is pressurized?