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Fuel Tank Pressure Test

Stockmanreef

Well Known Member
I have read a few posts about the balloon test and the manometer test. I am in the process of doing the balloon test. I have a balloon inflated to about 10" and it has been inflated for 48 hours without deflating. After reading several posts about tank testing. I am concerned that my "test" is not going to find leaks.

Maybe I should blow the balloon up more.

Is a manometer test up to 1 psi worth the effort?

Thanks
ken
 
My take is that a balloon that stays inflated for 48 hours is a good sign. But the purpose of the balloon is to allow you to pressurize the tank without over-pressurizing it. Too much pressure and the balloon will pop. While the balloon is inflated, test every joint and connection with soapy water or "Snoop" leak detector solution($11 from Amazon and works better than soapy water). Slightly open one connection as a test. Especially with Snoop, the tiniest leak will yield a bubble. No bubbles, no leaks, and no need to keep the balloon inflated.
 
I agree that a balloon hat stays inflated for 48 hours is a great sign. Of course, the truly best way to test is to put the tank in the orientation (dihedral and all) of flight and fill with fuel and leave for a week or two. There are obvious hazards with this form of testing, though.
 
My method

I had a leak that was, for me very hard to locate. It was at the corner junction of the back baffle, the top skin and the inboard baffle. It seemed to be present only with a fair degree of pressurization. I missed it on the soapy water bubble test.

How I found it was by connecting a short length of latex tubing to the tire stem with the central core removed from the stem, so there was no internal resistance, blowing hard on the tubing to pressurize the tank and then clamping the tubing with a hemostat. Don't worry about "over pressurizing" this way unless you are some sort of mutant opera singer or trumpet player; you would be hard pressed to get to 1 psi. I can only just inflate some balloons I used for testing). Then I waited until my wife wasn't home and dunked the tank into the hot tub, one seam at a time (tank was pretty bouyant). It was akward but it was pretty obvious where the little trails (x2) of air were coming from.

That said, a 10 inch balloon at 48 hours is a pretty reliable sign of a good tank, in my opinion.

I dried the tank thoroughly. And I changed the hot tub water.
 
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I had a pin hole leak in the baffle joint on one of my tanks. Once I found the leak I realized how small the hole was. It was an air bubble of sorts, maybe from the solvent. Anyway with that small leak there is no way that the balloon would stay inflated for 48 hours. I'd say your tanks are good to go.
 
Thanks for the replies. I "snooped" the entire tank and it looked good. Leaving the balloon on for another 24 hours. Just to see.
 
Tanks are Good, But...

Pressure inside the tank is now fixed. With changing outside barometric pressure (weather now moving thru lower Michigan), you should see the balloon change size, but not deflate.
Terry, CFI
RV9A N323TP
 
I have quickbuild wings. I did the balloon test and the balloon defalted in 24 hours on both tanks. I used soapy water and could not find a leak. I just ordered some Snoop and will try again.

I did a visual inspection inside the tanks with a borescope and they appear to be well sealed.

However, my question is how many others have found that their quickbuild tanks leaked? Is this common? Just curious if there is a particular location I should target for closer inspection.
 
Another small piece of advice.

When using the "balloon" test, blow up another balloon from the same package to the same size.
Many balloons are slightly porous and will deflate a small amount on their own.
By using two balloons from the same batch, you can compare the one on the tank with one off the tank.
 
I have quickbuild wings. I did the balloon test and the balloon defalted in 24 hours on both tanks. I used soapy water and could not find a leak. I just ordered some Snoop and will try again.
.

My initial leak was the seal on the fuel cap. Put some clear packing tape over that fuel cap. The next leak was the balloon attachment. Mel's idea is good. I left the tank indoors in an empty bathtub where the house temp is more constant. I let the end of the resting balloon touch an item lightly so I could see if any change occurred by it pulling away from the item. Good luck.
 
When I tested my tanks, I used a friend's manometer. I also taped over the fuel caps to rule out any potential issues with them.

The first results were very disappointing, until I realized the external factors and how they were impacting test results. Once I started recording temperature and pressure, I was able to understand why the manometer readings weren't consistent. I also learned that my basement temperature and pressure wasn't as consistent as I thought.

I did have a leak in each one of my tanks, which I couldn't locate with soapy water. Not wanting to take on the risk or expense of filling the tanks with
100LL, I filled the tanks with water. I added food coloring highlight the leaks. After the tanks sat on the bench for a couple days, I was able to locate and fix both leaks.

I've been fortunate in that for the last two years, the tanks have had no issues holding fuel. No paint blisters yet either.
 
I have had my balloon inflated over 2 months with no change. I am having a hard time seeing the physics of how I could have a leak! For those of you that are saying the balloon test is no good, please explain.
 
Ballons leak. I have difficulty understanding how a ballon can stay inflated for months. Party ballons leak down in 1 or 2 days. A manometer can be set up so it wont leak. I also put duct tape over the filler caps and over a few days found leaks where the duct tape overlapped. Solution was more duct tape at 90 degrees to the first. Properly set up, you can pressure the tank accurately with a manometer. One foot column of water is about 0.48 psi, if I recall correctly. Over several days, I saw variations that accurately reflected changes in barometric pressure and in temperature. RMMV.
 
Manometer

Ballons leak. I have difficulty understanding how a ballon can stay inflated for months. Party ballons leak down in 1 or 2 days. A manometer can be set up so it wont leak. I also put duct tape over the filler caps and over a few days found leaks where the duct tape overlapped. Solution was more duct tape at 90 degrees to the first. Properly set up, you can pressure the tank accurately with a manometer. One foot column of water is about 0.48 psi, if I recall correctly. Over several days, I saw variations that accurately reflected changes in barometric pressure and in temperature. RMMV.

That's how I tested mine. I tested both at the same time. Two Vans test kits. Two short pieces of aluminum tubing flared with a fitting for the vent connections. Two 10' sections of plastic tubing. Two small hose clamps. One scrap board. 27" total is 1 psi. 13.5" displaced on either side. I left them for at least 1 month. Small changes due to atmospheric pressure and temperature but no massive loss of pressure indicating a leak. Easy test.
 
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Well Brad I must have great balloons. Inflated 2 months ago, still inflated at the same size. I still haven't had my question answered: If air molecules cannot escape in two months, how will the fuel escape? Maybe I have the best balloons in history!
 
Bill, I did not mean to impune your integrity, just that of your balloons. I suspect that when you remove them, you will find you have stretched balloons that are holding very little pressure. Ballons may be a good way to avoid over pressurizing the tank, but unless you have a manometer or a pressure gauge, how do you know at what pressure you are testing the tank? One psi may be plenty air pressure to detect leaks and one tenth psi may make leak detecting much more difficult, and maybe ineffective.
 
Well Brad I must have great balloons. Inflated 2 months ago, still inflated at the same size. I still haven't had my question answered: If air molecules cannot escape in two months, how will the fuel escape? Maybe I have the best balloons in history!

Bill, I did not mean to impune your integrity, just that of your balloons. I suspect that when you remove them, you will find you have stretched balloons that are holding very little pressure. Ballons may be a good way to avoid over pressurizing the tank, but unless you have a manometer or a pressure gauge, how do you know at what pressure you are testing the tank? One psi may be plenty air pressure to detect leaks and one tenth psi may make leak detecting much more difficult, and maybe ineffective.
Except for the fact that a balloon may stay inflated over a long period of time is a good sign that you are retaining pressure, the balloon is NOT the test. The soapy water and looking for air bubbles IS the test for leaks. As others have said, the balloon's purpose is to serve as a relief valve. If the pressure expands too much during the time the tank is pressurized, the balloon will burst before any seams on the tank will.
 
Just a minor correction Brad, a 1" square column of water 1' high weighs .433 lbs. You were close though! :D
 
If the balloon stays inflated for 48 hours, I would say you are good to go or fill it with fuel to find leaks.

Has anyone here ever just chucked their first set of tanks and started over again?

I have been chasing pinhole leaks in the back baffling for almost a month. I ended up cutting 5" holes in the back baffling so I could reseal the baffles. Still had some pin hole leaks.

If I could start over again knowing what I know now, I think I could build an awesome set of tanks in about a week.

I'm guessing $600-700 for all the parts.
 
If the balloon stays inflated for 48 hours, I would say you are good to go or fill it with fuel to find leaks.

Has anyone here ever just chucked their first set of tanks and started over again?

I have been chasing pinhole leaks in the back baffling for almost a month. I ended up cutting 5" holes in the back baffling so I could reseal the baffles. Still had some pin hole leaks.

If I could start over again knowing what I know now, I think I could build an awesome set of tanks in about a week.

I'm guessing $600-700 for all the parts.
I have had my left tank off 7 times now. It is off now, as a matter of fact. The right tank has never leaked a drop since day one. The left tank is another story. Of course the left tank was the first one I built. Cutting the holes in the back baffle is the only way I was able to seal the pin hole leaks along the rear baffle. Knock on wood, I have not seen any further leaks back there since cutting the holes. None the less, I have the tank off again because of a leak in another location.

I have also considered making a new tank. My concern with doing so involves the Z-brackets and the nut plates. I am concerned they would not line up exactly as needed with the bolt holes on the wing spar. If I new I could have them line up as good as they do now I would consider building new ones. I also have return fuel lines so would have to deal with that aspect of the new build as well. So far I am still dealing with repairs rather than rebuild but it is a consideration still if I continue to have problems.
 
Fuel Tank Leaks

If the balloon stays inflated for 48 hours, I would say you are good to go or fill it with fuel to find leaks.

Has anyone here ever just chucked their first set of tanks and started over again?

I have been chasing pinhole leaks in the back baffling for almost a month. I ended up cutting 5" holes in the back baffling so I could reseal the baffles. Still had some pin hole leaks.

If I could start over again knowing what I know now, I think I could build an awesome set of tanks in about a week.

I'm guessing $600-700 for all the parts.



This thread resurrected .... I agree 100%, knowing what I know now, I think I could build an awesome set of tanks in a week also. I built mine a couple years ago and now finally going back to repair a baffle leak. If I build another set, I'm using Rick's method for sure.

http://www.vansairforce.com/community/showthread.php?t=7602

Doug
RV-7
Firewall Forward
 
If the balloon stays inflated for 48 hours, I would say you are good to go or fill it with fuel to find leaks.

Has anyone here ever just chucked their first set of tanks and started over again?

I have been chasing pinhole leaks in the back baffling for almost a month. I ended up cutting 5" holes in the back baffling so I could reseal the baffles. Still had some pin hole leaks.

If I could start over again knowing what I know now, I think I could build an awesome set of tanks in about a week.

I'm guessing $600-700 for all the parts.

What do you think you did wrong on the first tank? What would/did you do differently?
 
Your experience is most frustrating for sure.

A way to look at it is to image how fuel can escape from tank. A most obvious point is where a rivet penetrates the skin, next is along the aft baffle to skin corner joint and end rib joints to skin.

If each rivet hole has proseal in it and the inside head is encapsulated, no fuel will escape there. The area between rivet holes along the internal rib is not critical, there is no hole in the skin to leak. Fuel will only escape through a rivet hole. The end rib joints to skin do need attention though as one side is the out side of the tank. These areas are accessible so the joint can be inspected for adequate sealant.

A key to no leaks is don't skimp on the sealant. There are a few guys who have worked out techniques to make the job look great but the cosmetics inside the tank is not important. No leaks is important. Also, the Rick Galati method of fay sealing is a good idea because more sealant stays between the parts, it is not squeezed out as happens if the parts are riveted with wet sealant.

The area where most leaks occur is at the aft baffle. When it is slid into place there is no way to know how well the internal corner with the skin is sealed. The best way to insure it is sealed is to use lots of sealant when doing it. I also turn the tank up right after it is set so the aft baffle is down, that lets gravity work in your favor to seal that internal joint. At least any extra sealant won't run down the skin wall but settle into the joint.

It is also good technique to rough up the rib and skin surfaces where they meet. 100 grit will do the job. Proseal does no like a smooth surface, it will release easily.
 
My Balloon is deflating within 2 hours but no bubbles

Hello All:

I have been researching this but of course everyone has different circumstances. I have just tested my first tank. I used my air compressor and turned it down all the way just so I would feel small bits of air coming from the nozzle (did not even register PSI on the guage). I then double zip tied balloon to the vent line. Capped off all fuel return and supply lines with AN fittings and teflon tape etc.
Blew air into the fuel strainer and allowed balloon to inflate to about 10" diameter. I sprayed the **** out of the tank with soapy water with a flashlight to see better. ABSOLUTELY NO BUBBLES ANYWHERE! I did this several times.

I was super excited and thought I had a leak free tank:)

I spoke to soon :-( :-( My balloon was deflated within 2 hours. My fuel cap was taped over with masking tape. I sprayed edges of the tape and no bubbles.....

SO WHY IS THE BALLOON DEFLATING?? I had to take a break for the night because I was so furious haha.

I did this test several times and approx 2-3 hours for balloon to slowly deflate. It was done approx 70 degrees in my garage with blue skies outside.....don't think this will have and influence .

Perhaps trying different balloon and wrap it better around the vent line fitting. I am pretty sure its tight around the fitting because I also sprayed the fitting and no bubbles from where balloon is connected.

I was told I should build a manometer but how will this help? Anyone have any links to fabricate home made manometer?

WHY is this happening. No bubbles but deflating balloon.

ANY help or tips will greatly be appreciated:)
 
Hello All:

I have been researching this but of course everyone has different circumstances. I have just tested my first tank. I used my air compressor and turned it down all the way just so I would feel small bits of air coming from the nozzle (did not even register PSI on the guage). I then double zip tied balloon to the vent line. Capped off all fuel return and supply lines with AN fittings and teflon tape etc.
Blew air into the fuel strainer and allowed balloon to inflate to about 10" diameter. I sprayed the **** out of the tank with soapy water with a flashlight to see better. ABSOLUTELY NO BUBBLES ANYWHERE! I did this several times.

I was super excited and thought I had a leak free tank:)

I spoke to soon :-( :-( My balloon was deflated within 2 hours. My fuel cap was taped over with masking tape. I sprayed edges of the tape and no bubbles.....

SO WHY IS THE BALLOON DEFLATING?? I had to take a break for the night because I was so furious haha.

I did this test several times and approx 2-3 hours for balloon to slowly deflate. It was done approx 70 degrees in my garage with blue skies outside.....don't think this will have and influence .

Perhaps trying different balloon and wrap it better around the vent line fitting. I am pretty sure its tight around the fitting because I also sprayed the fitting and no bubbles from where balloon is connected.

I was told I should build a manometer but how will this help? Anyone have any links to fabricate home made manometer?

WHY is this happening. No bubbles but deflating balloon.

ANY help or tips will greatly be appreciated:)

Soapy water is not the best leak detection fluid. SNOOP is what we used in the oil and gas industry. BUT, if you stop by your local propane supplier, they will give/sell you what they use. Either way these detection products are much better that what your using.
 
Not sure

Not sure why people aren’t understanding the reason for the balloon; it isn’t for determining a leak (although if you have a big leak, it will).

The leak check is going over all of the joints and rivets with a bubble solution. Yes, the commercially available ones used in hvac or gas industries works much better than soap and water…
 
Hello All:

I have been researching this but of course everyone has different circumstances. I have just tested my first tank. I used my air compressor and turned it down all the way just so I would feel small bits of air coming from the nozzle (did not even register PSI on the guage). I then double zip tied balloon to the vent line. Capped off all fuel return and supply lines with AN fittings and teflon tape etc.
Blew air into the fuel strainer and allowed balloon to inflate to about 10" diameter. I sprayed the **** out of the tank with soapy water with a flashlight to see better. ABSOLUTELY NO BUBBLES ANYWHERE! I did this several times.

I was super excited and thought I had a leak free tank:)

I spoke to soon :-( :-( My balloon was deflated within 2 hours. My fuel cap was taped over with masking tape. I sprayed edges of the tape and no bubbles.....

SO WHY IS THE BALLOON DEFLATING?? I had to take a break for the night because I was so furious haha.

I did this test several times and approx 2-3 hours for balloon to slowly deflate. It was done approx 70 degrees in my garage with blue skies outside.....don't think this will have and influence .

Perhaps trying different balloon and wrap it better around the vent line fitting. I am pretty sure its tight around the fitting because I also sprayed the fitting and no bubbles from where balloon is connected.

I was told I should build a manometer but how will this help? Anyone have any links to fabricate home made manometer?

WHY is this happening. No bubbles but deflating balloon.

ANY help or tips will greatly be appreciated:)

I think you will need more pressure than that provided by a balloon to see bubbles at leak points. Make a manometer and put .5-1 PSI in the tank. A manometer is just a hose with water in it and a way to measure the water deflection relative to static. Youtube will help. Google will give a tool for converting inches of H2O to PSI. As mentioned above the specialized solutions will work better at low pressure than dish soap. What are you doing to cover the fuel cap. Those are almost universally unable to hold .5-1 psi of pressure. If you have an auto mechanic buddy, see if you can borrow his smoke machine. That is what we use on evap leaks where they are minor enough that bubbles don't work but still enough to throw a code.
 
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Not sure why people aren’t understanding the reason for the balloon; it isn’t for determining a leak (although if you have a big leak, it will).

Please enlighten us. What IS the reason for the balloon? While I don't use that method, it was my understanding as well that is was to check for leaks.
 
The balloon is to keep you from popping your tanks. Think about what couple psi adds up to over the surface of the tank. More than one builder learned that the hard way.

In every case (luckily for me) the balloon interface is what was leaking. I made a short tube fitting and put the balloon on the tube.
 
The balloon is to keep you from popping your tanks. Think about what couple psi adds up to over the surface of the tank. More than one builder learned that the hard way.

In every case (luckily for me) the balloon interface is what was leaking. I made a short tube fitting and put the balloon on the tube.

Yep.

Think about it in terms of finding leaks; unless you have a huge leak, that balloon will tell you very little. In fact, it will expand and contract with temperature and local pressure. Not to mention the fact that the balloon rubber is permeable to air, ie it will deflate over time, naturally. Don’t believe me? Blow up a balloon and let it sit…

If you are using the balloon as a leak check, how do you reconcile the external pressure and temperature variations? How do you reconcile the permeability of the balloon rubber? How do you even observe a seep around a single rivet? You can’t do it looking at a balloon.

A manometer will also show local variations in pressure and temperature.

No, the way to look for leaks is with a bubble solution…and the hvac products work really well.
 
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