M

Mark Jackson

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I am about finished with riveting and fitting out the fuel tanks (RV-8). Before installing the back, is there any reason not to put the tank in the cradle and try a filling them with water to check for leaks/drips?

Would seem to be much easier to deal with before the back is on than after.
 
It would seem to me that when they leak, they leak where at back baffle area. So testing before they are complete would not help you there. Put a dab of sealant over each rivet tail and nice filets where rib edges meet skins etc and you will likely be fine.

Bevan
 
Bevan said:
It would seem to me that when they leak, they leak where at back baffle area. So testing before they are complete would not help you there. Put a dab of sealant over each rivet tail and nice filets where rib edges meet skins etc and you will likely be fine.

Bevan
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+1 My only leak was one skin to baffle rivet. Also, water might not find the smaller leaks; water has higher surface tension than gas and will not leak in some places where gasoline would. I thought about doing this kind of test with gas, but decided that the danger and cost wasn't worth it.
 
My thought too...

For what it?s worth? I had the same thought and found a thread here (can't find it now though) that had many posts discussing the differences in molecular size between water (larger) and fuel (smaller), as well as the differences in cohesive properties of water (more cohesive) vs. fuel (less cohesive). It was the consensus of the thread that testing with water would not prove whether or not the same tank would hold fuel without leaking because of the differences. I would almost think it would be worth the fuel cost to fill a tank as you describe (in the cradle, without the baffle attached) to pre-find any of the forward leaks?and then clean the tank out with soap/water, etc. to remove the fuel. But then again, I sealed one of my tanks last week without doing the fuel test and will be sealing the other one this weekend. :)
 
If you want a really good method, try www.our7a.com

Hello -

Don't have an exact link, but you can check out my brother's web site at www.our7a.com - that is his builder's log - I believe he had a very good description (including equations for temperature change) showing how to pressure-test with air and a 'U'-shaped tube with water in the bottom of the 'U'. The difference in water height is a precise measurement of the tank's pressure. You can account (compensate for) for differences in height from one day to another by monitoring the temperature each time you take a reading and then using the 'delta T' to subtract-out any temperature induced error - a VERY effective method if done properly. Used the same technique to test my tanks and found a SMALL leak - fortunately was able to fix without opening the tank, since it was near one of the fuel fittings on the 'root rib' (easy fix by reaching in the cover plate).

Chris
 
I did test it in the manner you described with gasoline. I was extremely careful, but I have to admit I didn't feel very comfortable doing it. I used four 5 gal. gas cans to fill it up. The cans were relatively heavy as I was trying to do this very carefully. The vapors coming off the top made me kind of nervous. Also, if I had a leak, it would have been difficult to detect as the gas isn't blue like AVGAS.

If I were to do this again, and I don't think I would. I would have a big fire extinguisher nearby, do it outside away from the house or hangar, ground the tank and the can, and dye the gas your favorite color or use AVGAS. IMHO, it isn't worth the dangers. It seemed like a good idea at the time.

Jerry Esquenazi
RV-8 N84JE
 
I didn't have any problem with the baffles -- I think I used a whole can of ProSeal on each tank.

The only leak I had was a weeping rivet was a leading edge bottom rivet. But the thing is, it didn't start leaking for months after I filled the tank with fuel.

And it was such a small leak that the only way I discovered it was seeing the blue stain around a rivet head.

Unless it's gushing out an open wound, I don't think water is going to tell you much because you're not going to be able to see it in the most likely type of leak you'll have -- a tiny one.
 
chriscencula said:
Hello -

Don't have an exact link, but you can check out my brother's web site at www.our7a.com - that is his builder's log - I believe he had a very good description (including equations for temperature change) showing how to pressure-test with air and a 'U'-shaped tube with water in the bottom of the 'U'. The difference in water height is a precise measurement of the tank's pressure. You can account (compensate for) for differences in height from one day to another by monitoring the temperature each time you take a reading and then using the 'delta T' to subtract-out any temperature induced error - a VERY effective method if done properly. Used the same technique to test my tanks and found a SMALL leak - fortunately was able to fix without opening the tank, since it was near one of the fuel fittings on the 'root rib' (easy fix by reaching in the cover plate).
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I used Mike's manometer as well, before he headed out west. Worked just fine and helped me find a leak in each tank. Fortunately, both were reachable through the filler, so I just dabbed on a little extra proseal.

bob
 
Mark Jackson said:
Before installing the back
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The tank leak test is done with the tank under slight pressure (1psi). You might find gross leaks without the tank being sealed and pressurized but probably not the tiny ones.

IMG_0672.JPG
 
Fuel tanks

I had leaks in my fuel tanks even after using 1.5 cans of proseal. I had many minor leaks that wasn't detectable with soapy water but kept failing the balloon test. Here is what I did: I put fuel in the tank, capped it off and set it in the sun. As the temperature rose, the pressure in the tank did as well. Fuel would weep from the leaky rivets. Most of my leaks were coming from the rivets in the skin to baffle area. After drilling out about 60 rivets, and making 3 5" holes in the baffle I finally passed the balloon test. The tanks were very frustrating for me. I spent about two years off and on trying to seal the tanks. What's worse is I used B-2 and B 1/2 in my career field in the Air Force (the equivalent to proseal). I am dreading the canopy! YMMV

Mark Jackson said:
I am about finished with riveting and fitting out the fuel tanks (RV-8). Before installing the back, is there any reason not to put the tank in the cradle and try a filling them with water to check for leaks/drips?

Would seem to be much easier to deal with before the back is on than after.
Click to expand...
 
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