[vineyridge]

Pinhole. there is no rust on the tank outside. Pressure tank is 1000 gallons and runs both the farm and 4 houses, so it's a mini water system.

Can these things be repaired or am I looking at another pressure tank? Apparently welded patches are kind of iffy, depending on the corrosion inside the tank. I can say that JB Weld Water tank repair putty will not adhere to the steel, and I've degreased, ground off all the paint and primer and roughened the surface of the steel.

[Tom King]

How much pressure does it have to hold, and are you sure it's on the pressure side of the system?

[FitToBeTied]

The pinhole only matters if it is in the bladder inside of the metal tank. If the bladder has a hole then you replace the tank. Its only a couple of hour process.

You can tell if it is the bladder if the pressure gauge is reading lower than normal. Normal should be between 50-60 lbs.

[vineyridge]

Bladder? What Bladder. Tank is just one big open steel tank (thousand gallons) that is maybe 25 years old; and the pressure switch is set to 35-60 lbs. There is no separation between the air and water. Hole is in a place where the air and water meet. Patch will be applied tomorrow morning, but the welders who came out said that they couldn't guarantee that they wouldn't make the problem much worse. However, they have patched water system tanks, and the welder has a side business in nothing but water well drilling and water systems. Mostly irrigation, and those don't use pressure tanks. So these guys are as close to experts as I could find here.

They are going to put an 8 inch patch over a pinhole. If that doesn't work, looks like a new pressure tank.

[Tom King]

Interesting. I'd like to know how it comes out. I'd probably try some 3M DP 100 ( but it requires a mixing gun, and it's something I keep around for various purposes-it's fixed quite a number of things around here, including a big sprayer tank) before I'd chance 32 inches of mig weld to be flawless.

http://www.grainger.com/Grainger/3M-...Adhesive-3L939

If that didn't hold, which I'd be very surprised, I'd try DP810, which I use for assembling golf clubs.
http://www.grainger.com/Grainger/3M-...X05?Pid=search

Some people use DP100 for golf clubs too, so either should be plenty strong enough. 810 just breaks down at lower heat, so I use it to make taking clubs apart easier with little worry about overheating a shaft.

Nothing I've ever put either on has ever broken down once. Working time for both is just a few minutes.

If it's just some minute flaw in the tank, this would hold. If it's rusting out substantially at the water line, there's probably no fix worth doing to it.

[vineyridge]

An auto guy that is very good has patched a plastic water cooler top for the dogs with some auto product that also uses a mixing gun, but there is no pressure involved with that. Maybe I really should have tried the plain JB Weld, which HAS worked on a 40 gallon glass lined pressure tank. I repaired it five or six years ago, and it seems to still be holding. But the big one is a potable water system for humans, and I'm just a bit nervous about chemical repairs.

[Belg]

Had a buddy of mine repaired a cracked valve seat on his kawa 900 with JB. Filled the crack, filed, lapped, and is afaik still on the road today.... Rather than weld the patch, I'd consider JB'ing it onto a depressurized tank and dealing w/no water for a day. You can't make a hole worse with JB

Other brainstorm idea. How bigs the hole? Could you pop a standard automotive valve stem into it?

[Tom King]

Marine Tex would hold even if there is a little dampness still there. None of these tube epoxies are as strong as the 3M adhesives, but I know of one outboard that's been running for years with a freeze crack in the block fixed with Marine Tex.

http://www.jamestowndistributors.com...-Tex+Rapid+Set