Water Tank vent problems

[Stuart Meyers]

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???

 

[lw395]

The pressure on the top of the tank is from the column of water in the filler pipe.
Say it's a metre from the deck to top of the tank? That gives you about 0.1bar of pressure, 1.5psi.
There are a lot of sq inches in the top of the tank.
Tanks with 'flat' panels will always balloon to some extent.

You have to allow for the pressure of water when the tank is half full and you're sailing through rough water. That could be more than the static pressure.

 

[Plum]

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???

I don't see how moving the vent higher up the tank will make any difference. It's the pressure from the weight of water that is distorting the flat panels of the tank. If the vent is the same height as the filler, and you are filling with a hose loose in the filler , then water will only ever come out of the vent when the tank is full to the filler neck, no matter where the vent is fitted to the tank. Where are the leaks occuring?

Www.solocoastalsailing.co.uk

 

[RichardS]

I don't see how moving the vent higher up the tank will make any difference. It's the pressure from the weight of water that is distorting the flat panels of the tank. If the vent is the same height as the filler, and you are filling with a hose loose in the filler , then water will only ever come out of the vent when the tank is full to the filler neck, no matter where the vent is fitted to the tank. Where are the leaks occuring?

Www.solocoastalsailing.co.uk

Indeed so. The position of the vent is irrelevant and is only there to allow the water to be drawn out without, in extremis, the sides bowing inwards. The only issue is the weight of water inside the tank and air pockets etc are not relevant as the tank is, presumably, open to atmosphere whilst being filled and will not build up further pressure once the filler cap is replaced.

If the bowing is causing an issue, the easiest solution might be a ratchet strap right around the middle of the tank.

Richard

 

[VicS]

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???

As said above the trouble is the extra pressure caused by the head of water in the filler ( and vent ) if you keep filling to the maximum

Try to stop filling once the water level has reached the height of the vent connection on the side of the tank. Draw off any excess if you fill above this point