Fuel system leak test

[Bcone1381]

I have installed fuel lines from the the wing root, thru the tee and on to the fuel selector and gascolator but have not yet checked the system for leaks. What is the best practice for doing this?

Do I install a small balloon on one of the line at the wing root, opening up the fuel selector valve, and introduce compressed air (My compressor has a regulator. I would set the regulator at about 10psi to prevent over pressurization) into the system until the balloon is inflated? Will a balloon create enough pressure to cause a fitting to bubble up some soapy water if its leaking?
fuel line.png

[Mark Goldberg]

I would just put some fuel in the tanks and let it flow. Check around for blue stain. If your system is gravity flow, then nothing is pressurized. Mark

[BTAZ]

10 PSI(even 5 psi) is too much, 3 psi is plenty. I just blew up the balloon, twisted the neck, put it on the fitting, and let it untwist.

During the final fitting of fuel lines(before the final wing mate and engine install) I put a balloon on the firewall side of the fuel feed thru and capped off the four lines at the wing root. I then checked all my fittings with soapy water and did have some "work" to be done getting everything tight. When done, the balloon hadn't changed at eight hours.

After installing the wings and connecting the tanks to the fuselage lines, I plugged the vents in the fuel caps and put a fitting into the quick drain location of one fuel tank. Set the fuel selector to "Off" which on my valve ties the two tanks together but isolates the valve to engine run(which had been tested earlier). Similar soapy water test of all joints and pass "criteria" of an unchanged balloon after eight hours.

Also, the final leaks will be very small. It isn't sufficient to just quickly brush on soapy water and have a quick look. Take your time and study each joint very closely far any "new bubble" that wasn't there when you brushed on the soap/water mix.

[Battson]

I would just put some fuel in the tanks and let it flow. Check around for blue stain. If your system is gravity flow, then nothing is pressurized. Mark

The balloon test didn't work for me.

I had leaks everywhere and the balloon test found none of them! The leaks were all too small, leaking too slowly, and distributed around the periphery of the joints (not localised at one point). The soapy water didn't show any bubbles before it dried out or ran off.

Do what Mark suggests, use fuel and leave it a few days at normal operating pressure. You find green stains where the leaks are. You can still use a balloon and compressed air to put a pressure head on the fuel.

[Bcone1381]

Very well. I will probably wait for a Party, steal some balloons, just because I am curious, then follow up with a real life leak test after the wings have been installed .

[BTAZ]

It did turn out to be a bit of a technique to find the leaks. It certainly isn't like finding a leak in a tire tube or a compressed air system.

I spent a couple days each on my tanks after initial welding chasing the seam welds and got a pretty good feel for "Balloon delta vs. leak size" and the final leaks(where the balloon only seemed to have changed after five hours or so) were tough to find. I persevered, getting to the point where the balloon would remain unchanged overnight at a minimum, and do seem to have found all of them. I really didn't want to have to weld on a tank that had already had fuel in it

As mentioned, one can't just brush on soapy water and take a quick look. I found I had to keep brushing on the suspect area, carefully looking for any bubbles that formed after I brushed. I also "marked the balloon by putting on a thin piece of masking tape a few inches long to detect the change in size. If the tape wrinkled, the balloon had shrunk. It can be seen on the balloon on the wing tank quick drain in the earlier post

But each to their own......

[Bcone1381]

Ka-Boom!!

Roger wilco on the masking tape and careful bubble detection. Its going to be a while until the wings are on the rest of the system is ready to hold fuel. Like I say, I am curious.

[Bdflies]

In high purity gas applications, we used 'Snoop' leak detector. https://www.swagelok.com/en/product/...-Leak-Detector. It doesn't dry as fast as soapy water and will suds up at the tiniest leaks. If you really want to chase leaks, use Helium instead of compressed air. I'm halfway joking about the Helium, but if you can make it tight with Helium, it's really tight!

Bill