Water Tank

[Paulam]

Hello re 1987 Catalina 36. My main water tank develops pressure when filling. Vent line is clear. Any ideas?

 

[Scott T-Bird]

What happens when you open the inspection port while filling?

 

[jssailem]

If your water pressure pump is off, then your filling water at a rate greater than the vent line can manage. You say the vent line is clear. Where does the vent line run?

• Is it kinked so that it shuts down the air escaping from the tank?
• Does the vent line vent into the open fill fitting? Are you putting water into the tank and the vent line at the same time?

 

[Ralph Johnstone]

Care to tell us exactly what evidence leads you to believe your vent line is clear ?

 

[Tally Ho]

I would think that one of two things could be happening…

1) The vent isn’t really clear….
2) You are filling faster than the vent can let air out of the tank.

Or maybe a combination of these 2.

Greg

 

[Paulam]

Thanks for getting back to me. I blew the vent line out with compressor. Then I blew through by mouth it is clear. Vents into cockpit. I have tried filling very slowly. Still builds pressure. With inspection cap off I have run the pump/tap, water level drops as you would expect. Turn tap off water level rises to top of inspection hole. The water is not coming from side tank. Level remains the same there. I would guess that if I kept doing this eventually the water level in the tank would drop and stay dropped.
This may have been going on since I have owned the boat 4 years. The only reason I got onto this now is I sprang a leak in the tank. This prompted me to look down there to see what was going on. Thats when I noticed the pressure. You can see a slight dome in tank. None of this makes sense but it is whats happening.

 

[Paulam]

Thanks for getting back to me. I blew the vent line out with compressor. Then I blew through by mouth it is clear. Vents into cockpit. I have tried filling very slowly. Still builds pressure. With inspection cap off I have run the pump/tap, water level drops as you would expect. Turn tap off water level rises to top of inspection hole. The water is not coming from side tank. Level remains the same there. I would guess that if I kept doing this eventually the water level in the tank would drop and stay dropped.
This may have been going on since I have owned the boat 4 years. The only reason I got onto this now is I sprang a leak in the tank. This prompted me to look down there to see what was going on. Thats when I noticed the pressure. You can see a slight dome in tank. None of this makes sense but it is whats happening.

PS i have seen water coming out the vent outlet.

 

[Tally Ho]

We must be missing something….

How many tanks do you have? How are they connected? Do you fill the tank with a hose in an open deck fill? Or do you have a city water hook up?

Does the tank have an inspection port you can open?

The pressure you are seeing does what? Spews water out of the deck fill? Is the tank full at that point?

Greg

 

[Scott T-Bird]

What makes you say the tank is pressurized? It sounds like your only evidence is a slight dome in the tank. That could be its natural condition ... particularly with summer heat. If you fill the tank nearly to the top with the inspection port closed, you should be able to hear a release of air by cracking open the inspection port if the tank is pressurized. If you don't detect any air escaping, it's not pressurized.

Also, if you have a feed to the pump from 2 separate tanks, you should close the valve to one tank and only draw from the other. For best practice, draw from just one tank at a time. I can't really follow what you were saying, but it sounds like you are connecting the 2 tanks and the water levels are merely equalizing. If this is what you are doing, you shouldn't. The pump doesn't work very well that way. I don't really know the explanation but I'm pretty sure that you are simply doubling friction losses in the feed lines when you leave both tanks open when pumping water. That has a bad effect on the pump and it pumps water less efficiently.