water tank vent problems

[redskycsy37]

I have a CSY37 and the Fiber glass water tanks swell up like a Balloon when I fill then to full. There is a 3/4"vent overflow about two inched from the top of the tank on the forward side next to the Fill but no water comes out until they are completely filled but at that point they start to Balloon and it is causing all kinds of stress problems / leaks etc. I think I need to move the Vent higher but can't put it out of the top because there is no room. it seems that there is a Air pocket at the top causing this problem! Should I punted a vented loop in ? but I don’t see how that would solve the problem! Any body with any Ideas would be most appreciated???

[Tellie]

If your tanks are swelling when filling your tanks I doubt the air vent is your issue. It's not a matter of the air not being able to escape and pressure building, but rather the weight of the water that is causing the swelling and leaks. Remember, water weighs a bit more than 8lbs a gallon. That's a lot of force exerting itself outward on all sides of your tank. Now add the motion of the Ocean and that weight gets thrown around quite a bit. If you're getting all kind of stress problems then it's time to have a pro look at the tank.

[peghall]

I suspect that whoever made this tank didn't know how to do it and that the tank walls are too thin to support the weight of the contents (8.333 lbs/gal)...'cuz a fiberglass tank shouldn't be able to swell.

But if he also made the fitting for the vent line diameter too small to allow air to escape at the same rate incoming water is displacing the air and/or also has several bends and/or loops in it, the vent could also be source of the problem.

--Peggie