Fuel tank pressure testing...

[kbalch]

I'll be installing the aft baffle on my left tank tonight and have begun thinking about pressure testing in a few days, post-cure.

Plans page 18-09 Step 1 & Figure 2 specify the use of a rubber hose and Fuel Air Tank Valve [Sic] to pressure test the tank. Also referenced is the Fuel Tank Test Kit and its alternate parts & included instructions. Hence my confusion.

If the plans are correct, how exactly does one apply air pressure to the valve on the rubber hose?

If the test kit parts and instructions are correct (they appear to be QB-specific and not directly relevant to my standard kit), then what of 18-09?

Perhaps we're meant to follow the plans, but utilize the test kit's instructions only regarding the spraying of soapy water on the pressurized tank...

I'm sufficiently nervous about my first tank turning out well without any plans-related agita.

[Nova RV]

Search here on VAF on using a manometer made from a length of clear tubing (Lowes). The spray and balloon method works to a point but balloons leak through their skin and won't hold pressure for a long time leaving you wondering if you have a leak or just the balloon leaking down. You can connect a manometer and leave it for a week if you like.

[Mudfly]

i followed the instructions that came with the balloon test kit. As you stated, they are a little different than shown in -14 plans. I used some rubber tape on the fuel fitting to help seal where the balloon attaches with hose clamp.
When installing the air valve to the tank drain fitting, I used just a little permatex 2 and made sure to tighten just enough to seal. The threads didn't seem to match each other very well , and I didn't want to damage threads on the drain fitting. Remember, balloon is just technically there to prevent over-pressurizing tank for the soapy water test. However, it is a good feeling to see the balloon still inflated after a couple of days

[kbalch]

That sounds good to me. I've already installed my drain valve (and definitely don't want to damage the drain fitting threads), so I'm planning to hose clamp the air valve to the rubber hose placed over the vent fitting. Balloon will go over the fuel fitting.

Given that both the manometer and the balloon are only there to function as pressure-relief and that both are sensitive to ambient conditions, I don't see any advantage to the manometer. The soapy water will tell the tale, one way or the other.

This whole tank adventure has really put the brakes on my wing kit progress. I got the left wing top skins riveted, leading edge installed, and right wing leading edge built and set aside in the first two weeks on the wing kit. I've now spent 2.5 more weeks getting the left tank to this point and all the right tank components ready to seal up once the assembly cradle is clear.

That said, my fuselage kit won't be ready until late October, so I have plenty of time to fill.

[rvbuilder2002]

Originally Posted by Nova RV

Search here on VAF on using a manometer made from a length of clear tubing (Lowes). The spray and balloon method works to a point but balloons leak through their skin and won't hold pressure for a long time leaving you wondering if you have a leak or just the balloon leaking down. You can connect a manometer and leave it for a week if you like.

I agree there are many ways to accomplish the testing, but connecting a manometer and watching it for a week is no different than watching a home weather station. The reading will go up and down with changes in air temp and barometric pressure.
Then you can be left guessing whether it was caused by a change in the weather or an actual leak.

[sibriggs]

The most through test is filling the tank with 100LL let it sit for a number of days and look for any stains. Sometimes air doesn't seem to find ways in and out that fuel can.

Of course you must insure all the proper grounding and safety is complied with.

I've done the balloon test with no leak results and still tiny stains show up when fuel is added in the plane later.

[kbalch]

Originally Posted by sibriggs

The most through test is filling the tank with 100LL let it sit for a number of days and look for any stains. Sometimes air doesn't seem to find ways in and out that fuel can.

Of course you must insure all the proper grounding and safety is complied with.

I've done the balloon test with no leak results and still tiny stains show up when fuel is added in the plane later.

I hear what you're saying, though building at home as I am, I have no ready means of transporting 25 gallons of 100LL, nevermind attending to the necessary safety precautions. To say nothing of manhandling a 150+ pound tank.

Any tiny stains found later will necessarily be dealt with as they present, probably with sealant or Loctite (for weeping rivets).

[Kyle Boatright]

Originally Posted by kbalch

I hear what you're saying, though building at home as I am, I have no ready means of transporting 25 gallons of 100LL, nevermind attending to the necessary safety precautions. To say nothing of manhandling a 150+ pound tank.

Any tiny stains found later will necessarily be dealt with as they present, probably with sealant or Loctite (for weeping rivets).

On the other hand, you could put a few (3?) gallons in it, stand it on one end for a day or so, stand it on the other end for a day or so, and then stand it where the rear baffle is down for a day or so. The end ribs and rear baffle are the most likely spots for a leak.

Me? I trust the balloon test.

[PilotjohnS]

I used a manometer. I pressurized it by blowing into the manometer and then pushing a swig of water in as my lost breath.

[jibby212]

I used the manometer method with both tanks, this way you can identify a loss in pressure. Thankfully my tanks rose and fell identically for 3 days.