Fuel tank leak testing with water before closing out?

N546RV · #1 10-12-2014, 03:02 PM

OK, so while searching for something-or-other earlier today, I saw where someone mentioned performing a leak test on his tanks prior to installing the baffle. He did this by (presumably) placing the tank in the cradle and filling it with water. Apparently he was able to find a few leaky rivets this way and fix them prior to installing the baffle.

So now I'm trying to decide whether this is worth my time to do. Honestly, I'm leaning away from it, but I figure it could make for an interesting discussion.

Pros:

Possibly identify minor leaks while they're still accessible and can be fixed. Maybe avoid needing to create access holes in the baffle after the fact.

Cons:

Fuel is less dense than water and thus presumably more likely to find a leak than water. So while the water might not leak, this doesn't necessarily mean that fuel won't.
Increased timeline for completing tank closeout. For example, I expect to install the end ribs this week, which would allow me to do the baffles this weekend - unless I do this leak test, in which case I'd feel compelled to let the tanks sit for a couple weeks.

I suppose my overall take on this is that the water test seems like an OK way to find gross leaks, but by no means would it be a true indicator of whether the tanks were intact. If anything, the presence of water leaks seems like it might point to systemic problems with sealing technique.

On the other hand, I reallyreallyreallyreally don't want my tanks to leak. I went out today and touched up several locations that looked sketchy to me. So the water test appeals to me from that perspective - but again, thinking rationally, I don't think it's truly worth it.

What say you all? Are leaks a smaller problem than I think they are? Do I need to just shut up, close the things, and pressure test down the road?

(I think I'm just overthinking all of this because I'm nervous about leaks)

Kyle Boatright · #2 10-12-2014, 03:12 PM

I filled mine with water prior to attaching the aft bulkhead , found no leaks, and closed 'em.

I figure it is one of those things that takes 5 minutes and can't hurt.

Dan Langhout · #3 10-12-2014, 06:47 PM

Quote:

Originally Posted by Kyle Boatright

I filled mine with water prior to attaching the aft bulkhead , found no leaks, and closed 'em.

I figure it is one of those things that takes 5 minutes and can't hurt.

However, I ended up with a small leak in the corner with the aft baffle when I did my final leak testing with air. Tanks have been holding fuel now for 2-1/2 months and 40 flight hours with no leaks - so far so good.

tracy · #4 10-12-2014, 07:55 PM

I wonder how many have developed leaks after an initial leak free test, and how long it took to develop them?

Mike H · #5 10-12-2014, 08:08 PM

I wonder how many tanks end up leaking because too much sealant is used between the ribs/baffle and the skin which could make the structure flex and leak around the rivets. Then add in the poor technique of clecoing in the ribs wet and waiting for the sealant to cure before riveting.

N546RV · #6 10-12-2014, 11:50 PM

OK, good feedback, thanks! Kyle and others who've done the water leak test: How long did you let the sealant cure before doing the water test? I'd like to close the tanks this weekend if possible, but I don't want to potentially muck up sealant that's only slightly cured.

I'm thinking that if I focus, I can have the end ribs sealed and riveted Tuesday night. That could give me three full days of curing (in a hot Houston garage) before Saturday, when I could water test prior to installing the baffles. Alternatively, I could let the tanks cure for an extra week while I start working on the leading edges, maybe working on the landing light installation.

Kyle Boatright · #7 10-13-2014, 04:19 AM

Quote:

Originally Posted by N546RV

OK, good feedback, thanks! Kyle and others who've done the water leak test: How long did you let the sealant cure before doing the water test? I'd like to close the tanks this weekend if possible, but I don't want to potentially muck up sealant that's only slightly cured.

I'm thinking that if I focus, I can have the end ribs sealed and riveted Tuesday night. That could give me three full days of curing (in a hot Houston garage) before Saturday, when I could water test prior to installing the baffles. Alternatively, I could let the tanks cure for an extra week while I start working on the leading edges, maybe working on the landing light installation.

The "Thumbnail" test tells you when proseal is cured. Depending on ambient temperature and how "hot" you mixed the proseal, it could take a day to cure or a month.

TerryWighs · #8 10-14-2014, 05:34 PM

I just used a fabricated "Manometer".....All is well. Set up is on builder site link in wings section.

N941WR · #9 10-14-2014, 05:57 PM

When I was building I asked Van's about using water to test the tanks. They are adamant that you should not use water to test the tanks.

While I don't remember their exact words, it had to do with the possibility of residual water, possible corrosion, and that the viscosity of water isn't the same as fuel and that while the tanks might hold water, they may not hold fuel.

It was enough to convince me to use the balloon method after sealing everything.

In seven years the only leaks I have had were a number of rivets that blistered the top of the left tank. The reason for that was that just before painting I used MEK to remove excess proseal on just that area. Had I sanded the proseal off, I'm sure I would be preparing to repaint the top of that tank.

JimWoo50 · #10 10-14-2014, 07:37 PM

I poured about a gallon and a half in and stood tanks on either end and flat etc. I had one leaker in the rear baffle. If I read correctly and you have not completely finished your tanks make sure you are generous with the pro seal on the rear baffle and the tank mating surfaces. When you squeeze these surfaces together some of the sealant will get squeezed out. Good Luck!