Pressure holding at 15 inches of water after a 16 hour overnight soak but down from the 30 when I left the shop.
The initial plan was to test the 3/8" fuel supply line independently of the 1/4" return line which would have involved making a new test setup because the fittings are different sizes. After giving the test setup some thought, decided it was time to work smarter and not harder. It would be easy to loop the fuel return line to the supply line and pressurize both lines at the same time. So yet another trip to the local hardware store to procure some pieces of vinyl tubing and some hose clamps.
A loop of 1/2" OD 3/8" ID vinyl tubing was made to connect the fuel supply line at the aft end of the fuel pump to the smaller return fuel line’s center channel aft bulkhead fitting. Because of the modification I’m making to the fuel system by adding an additional fuel drain below the fuel tank, the fuel line between the tank and fuel pump is not installed yet, nor is the fuel return line from the bulkhead fitting to the fuel tank. So a small piece of 3/8” aluminum fuel line was flared on one end and attached onto the aft fitting on the fuel pump, the other end of the aluminum tube had a piece of 1/2" OD 3/8” ID vinyl tubing slid over it and secured with a hose clamp. A piece of 1/4" aluminum tubing was flared and attached onto the return fuel line’s center channel aft bulkhead fitting and a small piece of 3/8" OD 1/4" ID vinyl tubing was slid onto the end of the aluminum tube for use as an adapter. The end of the 1/2" vinyl looping tube was slid over the small piece of 3/8" vinyl and tightly clamped.
Picture of the vinyl tubing loop and associated parts. In my fingers is the small piece of 3/8" OD vinyl tube that will be used as an adapter between the 1/4" aluminum tubing and the 1/2" OD vinyl tubing.
The completed pressure test loop that ties the fuel pump to the fuel return line’s center channel aft bulkhead fitting.
Really did not think there was a fitting leaking because a lot of care was taken when making the flared fuel line fittings and they were all torqued to specifications plus a VERY THIN coating of fuel lube was placed on the mating surface of the fittings (not the threads) so they would not gull when they rotate during tightening … seems like the first end of the line that is tightened always twists a little while being tightened. The fuel on/off valve was moved to the on position, the return line capped off at the firewall shelf and the test pressure was brought up to 55 inches of water and appears to be holding there nicely … but time will tell.
Pressure brought up to 55 inches of water (which is approximately 2 psi) and appears to be holding nicely.
Tomorrow morning will tell the tale but as it appears now, the small air leak I was experiencing was apparently through the on/off valve because the other end was not capped off at that time.