Fresh water tank vent - geometrical problem - vent to bilge an option?

[rgranger]

#Peggie, I will check clearance on top of tank. Uniseal defintely an option.
#Sailme88, not sure I follow. If air does not get into the tank, the pump creates a vacuum above the water as the level goes down.

Hi @Fredct
Forum tip.... the site here uses the "@" instead of the "#" to ping a user.

 

[twistedskipper]

If air does not get into the tank, the pump creates a vacuum above the water as the level goes down.

I was wondering about this also. If the pump has enough power can air still be drawn in through the water in the vent line?

 

[Ron20324]

Air vents should run uphill, never below horizontal.

 

[Peggie Hall HeadMistress]

If air does not get into the tank, the pump creates a vacuum above the water as the level goes down.

The problem is, if the pump can't pull in any air, it creates a vacuum that won't let it pull anything out of the tank. So the level doesn't go down and you'll be trying to figure out why no water comes out of your faucets.

--Peggie

 

[sailme88]

#Peggie, I will check clearance on top of tank. Uniseal defintely an option.
#Sailme88, not sure I follow. If air does not get into the tank, the pump creates a vacuum above the water as the level goes down.

Let me restate it. When the vent line fills up from the tank there is still air over water and the pump will work.. A low spot in that vent line will stop the process unless the low spot is shallow and allows some air past it.

 

[TimFromLI]

I am not so sure that the pump can't overcome the vacuum in the tank to suck the water out of the vent line. Think about it, if the pump can pump water vertically 6 or 7 or even 10 feet then it can certainly overcome a vent line with water in it. Not to mention that the volume of air in the tank is very large, so how much of a vacuum could there be. Unless the vent line is blocked by a solid the vacuum should suck the water out.

 

[Davidasailor26]

Think about it, if the pump can pump water vertically 6 or 7 or even 10 feet then it can certainly overcome a vent line with water in it.

Exactly. For example here’s a mid-range marine fresh water pump- JABSCO 4GPM PAR-Max PLUS Freshwater Pump, 12V, 12A | West Marine. It claims to be self priming to 10’. That means it can suck up water against its own weight for 10’. There’s no way the loop in your vent is close to that, maybe a foot or so? And the 10’ self-prime is when the pump is only pulling air. In your case the pump has water in it, so it should be able to lift even more. If the vent has a wet clog in it then that changes things, but just water itself shouldn’t be a problem.