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Fuel Tank Test

A

AviatorJ

Well Known Member
I'm to the point that I need to test my QB Fuel tanks so I can put them back on the wings. Even though they should of been tested in the Philippines it's suggested (and I agree) that I need to test them as well. I'm going to use the 'Fuel Tank Pressure Testing' kit provided by Vans. Just have a fuel questions;

I'm using regular float fuel senders and installed those per the plans and used pro-seal for final attachment. I literally did that at lunch today so how much time do I need to wait for it to cure before pressure testing?

Below is a picture of the Kit-

IMG_2087.jpg


From what I understand you put a balloon on the fuel vent and the inflation stem on the bottom. How do I use the Blue cap and allen insert deal to close off the VA-141 flange hole? Am I supposed to connect something to that first?

Lastly do I use a hand tire pump to pressurize or can I use a compressor on a very low PSI setting and just watch the balloon so it doesn't over inflate?

Once I get this figured out I can do the soapy water spray and find any leaks... thanks!
 
I waited a week. Definitely don't use a compressor. Use a hand pump or a bicycle pump.

I don't recall if the cap in the kit will fit the fuel vent fitting or not. You may need to order one from ACF to fit the vent. If I remember correctly, i also had to order a plug for the fuel line fitting as well.
 
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Test kit

ERushing said:
I waited a week. Definitely don't use a compressor. Use a hand pump or a bicycle pump.

I don't recall if the cap in the kit will fit the fuel vent fitting or not. You may need to order one from ACF to fit the vent. If I remember correctly, i also had to order a plug for the fuel line fitting as well.
Click to expand...

The test kit comes with a plug for the drain with a shraeder valve, cap for the fuel line. You can make a connection for the vent with a piece of tubing. Use a balloon at the vent connection or make a home made manometer from a piece of plastic tubing. The beauty of the manometer is more precise pressure and monitor of change. I have details on the "Tanks" page of my blog if interested. Use kids bubbles in a spray bottle to check for leaks. They retain a bubble longer.
 
Is there a reason to not just use fuel to be sure? I tested mine about a year ago but getting ready to paint and I want to be 100% sure they do not leak before I paint them. My thought is to fill them up and see what happens!

Outside of course with a bucket of kitty litter and a tub to set it in.

Any reason to not test with fuel?
 
The balloon works fairly well. You can add air from a compressor. The balloon makes sure you don't over pressurize.

I personally like testing with fuel. You can let it sit for a week if necessary and look for stains. I like to set it at the angle that the plane sits with dihedral so there is the right head pressure at all points in the tank.

I would let the proseal cure for at least one overnight. To see how well cured it is, press your fingernail into it and see how quickly it returns to its original shape. If it doesn't at all, it's not ready. If it does quickly, it is ready.
 
I feel that air (or nitrogen) is a better test medium than fuel. It's lighter and thinner than fuel, and will indicate a leak where fuel may not. YMMV

-Marc
 
wirejock said:
The test kit comes with a plug for the drain with a shraeder valve, cap for the fuel line. You can make a connection for the vent with a piece of tubing. Use a balloon at the vent connection or make a home made manometer from a piece of plastic tubing. The beauty of the manometer is more precise pressure and monitor of change. I have details on the "Tanks" page of my blog if interested. Use kids bubbles in a spray bottle to check for leaks. They retain a bubble longer.
Click to expand...

I'll check your site - I'm guessing I need to install the VA-261 Fuel Strainer fitting to use the cap from the kit then..?

rockwoodrv9 said:
Any reason to not test with fuel?
Click to expand...

For me it would be logistically challenging. Not only filling them up but then emptying them in my 172 when I was done. Can it be done with water and food coloring?
 
AviatorJ said:
I
For me it would be logistically challenging. Not only filling them up but then emptying them in my 172 when I was done. Can it be done with water and food coloring?
Click to expand...

No. Water has more surface tension than av gas. (Wants to 'bead up'). A small hole may leak gas but not water. Of course using air is an even more stringent test.
 
I answered my own question, if the filters are installed in the tank then the cap fits... I will try the balloon test when this stuff cures.
 
Using air, heat on the tank from the sun or just temp change will cause the balloon to vary in size. Even a balloon will lose some air just through the sides of the balloon. I just didn't think I could trust the balloon test. Maybe a micro scale pressure gauge would work? I did the balloon test and was reasonable satisfied but going to do it with fuel too - just to be sure.
 
I thought the purpose of the balloon was to let you know when there was positive pressure in the tank as well as when you're over filling it.
 
AviatorJ said:
I thought the purpose of the balloon was to let you know when there was positive pressure in the tank as well as when you're over filling it.
Click to expand...

I believe you are right. I just want to be sure it holds fuel. The balloon will change depending on the pressure. I just want to put my mind at ease before I paint the tanks.
 
The primary purpose of the balloon is to act as a pressure relief valve so when you pressurize the tank you don't blow it up. There's a number things that can cause the balloon to deflate besides a leak which is why there's more to the test then simply putting air in the tank.
 
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Balloon

The balloon is there primarily for relief. The change in temperature from morning to night will make it change so it really is not a valid indicator of if the tank leaks or not...
 
After filling up the tanks with air I left mine inside the house for about a week. The balloons hardly changed size as the temperature is pretty constant inside the house. They held air fine after I patched a gaping hole that I somehow missed prosealing the inboard nose rib on one of the tanks. I have not yet tested with fuel.
 
Went ahead and tested the tanks this afternoon. I utilized a compressor but had it down to the lowest PSI setting, then as I filled I watched the balloon to monitor the pressure.

I sprayed soapy water all over the place and had no bubbles or leaks on either tanks... well minus the area around the balloon since I just zip tied it.

Here's a picture- sorry it's sideways...
IMG_2092.jpg
 
monometer or ballon...temp matters....

The tank is one big balloon, so does not matter how accurate of an instrument you attach, it will change with temp, just good ol chemistry, PV=nRT. So temp changes are fine, just make measurements at the same temperature, balloon or the most sophisticated monometer will agree. Use Helium balloons, much less likely to lose air too. Or if your really into ancient (and reliable) methods, use water in a u-tube, pressurize to x inches up in the exit tube of water and away you go. Has the nice advantage of pressure relief as mentioned in earlier reply. I also did the fuel test in the -7 and will do so in the 10, just piece of mind and so easy to do. For those who really like to challenge their sealing job, fill with helium, much faster diffusion rate than air (nitrogen/oxygen)!
Cheers, Mike
 
Just to clarify I only used the balloon to ensure I didn't over pressurize the tank. Soapy water and the search for bubbles was my leak detection gauge.
 
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