Vacuum Valve for Water Tank

weephee · #1 (**permalink**) 04-17-2010

I just replaced my water tank and there is a vacuum line running from the top of the tank to just below the deck and then loops and drops down a few inches. The purpose of the line is to draw air into the tank as the water is being removed to prevent a vacuum. Question is when I fill the tank from the thru deck fitting what is to prevent water from spilling out the end of the vacuum line if I fill the filler hose to the deck level which is higher than the vacuum line loop. Should there not be a check valve or vacuum valve on the end of it If so, what is the valve called. I can't seem to find one. Thanks

PorFin · #2 (**permalink**) 04-17-2010

Wee,

The vent lines are normally attached to a vent fitting that goes through the hull well above the waterline. They look like this:

Funny these aren't already installed on your sailboat...

weephee · #3 (**permalink**) 04-17-2010

I have a vent for the waste tank but not the water tank. I'm thinking that a one way check valve should work??

PorFin · #4 (**permalink**) 04-17-2010

I think a check valve would be bad for a couple of reasons.

1. If it fails to close you'll get a lot of water in places you don't want it, namely inside the boat.

2. If it fails to open, you'll be fighting back pressure as you fill your tanks.

Installing a proper vent fitting isn't expensive or difficult, and takes all of the worry out of the equation. When your tanks are full, the water will safely flow out of the vent and down the outside of the boat.

redline · #5 (**permalink**) 04-17-2010

A simple vent fitting (same as fuel tank) will do. My previous (C&C33) had a fitting as shown above on the side of the hull, up near the toe-rail. My current (SO45.2) has a plastic through-hull somewhat hidden in the anchor well, I think so as to prevent any seawater incursions in heavy seas and/or heeling. Same effect, and if the tank is overfilled, water does come out the vent as well as the deck fill. No big deal, just proof the vent should be "outboard".

.

southshoreS24 · #6 (**permalink**) 04-17-2010

since an anchor well should be drained overboard also, the added benefit to putting the "vent" in there is that it too would drain outboard but leave less holes in the hull. IMHO looks better and is a better idea if possible with out much modification. I would only do this with fresh water vent.

mitiempo · #7 (**permalink**) 04-17-2010

One of the best solutions I've heard of for water tank vents is an inside vent either high in the head or running into the sink. If water tank vents are through hull types the tanks can be contaminated in rough sailing. Mounted high near the overhead in the head/closet area water will come out the sink spigot on the manual pump before it ever comes out the vent. Early Swans had the vents going into the sink like the pic below. On an offshore boat I would never have a water tank vent going overboard due to the risk of contamination.

MedSailor · #8 (**permalink**) 04-18-2010

Quote:

Originally Posted by mitiempo

One of the best solutions I've heard of for water tank vents is an inside vent either high in the head or running into the sink. If water tank vents are through hull types the tanks can be contaminated in rough sailing. Mounted high near the overhead in the head/closet area water will come out the sink spigot on the manual pump before it ever comes out the vent. Early Swans had the vents going into the sink like the pic below. On an offshore boat I would never have a water tank vent going overboard due to the risk of contamination.

Now THAT's a good idea. My boat has a weird home-grown vented loop thing that is supposed to drain into the bilge but really drains onto my dry goods in the cabinet shelf.

I've been avoiding drilling holes in the boat so haven't fixed it yet. The thought of seawater contamination never even occurred to me. Running it to the sink also saves me drilling more holes. I like it!

MedSailor

mitiempo · #9 (**permalink**) 04-18-2010

If you go the other route and put the vent near the overhead close to the centerline, say in the head area, the only way water would come out is if you were upside down - and then you would have other problems.

PorFin · #10 (**permalink**) 04-19-2010

Quote:

Originally Posted by mitiempo

One of the best solutions I've heard of for water tank vents is an inside vent either high in the head or running into the sink. If water tank vents are through hull types the tanks can be contaminated in rough sailing. Mounted high near the overhead in the head/closet area water will come out the sink spigot on the manual pump before it ever comes out the vent. Early Swans had the vents going into the sink like the pic below. On an offshore boat I would never have a water tank vent going overboard due to the risk of contamination.

I think this is a better solution.

Having the vent run inside the boat also greatly reduces the chance of a wasp/mud dauber (or other critter) plugging the line, which is a pretty common occurance for us.