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Old 02-04-2013
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Location of water tank breather pipe

My Bristol 31.1s fresh water tanks are vented with a loop that goes from the lower tank (in the bilge) up to deck level, then down again and ends a foot above the cabin sole, inside the area under the galley sink.

It's quite a good arrangement, except that when I fill the water tanks, any excess soaks the area under the galley sink - and the damp is starting to rot the sole.

Any reason why they didn't extend the pipe all the way into the bilge? I'm thinking of doing this.

Configuration is : 1 tank under the V berth, second tank lower down in the bilge. The bow tank drains into the bilge tank. Lower tank is vented.
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Last edited by MarkSF; 02-04-2013 at 03:10 PM.
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Re: Location of water tank breather pipe

Cut the hose up near deck level & put a 1 way plastic check valve on it.
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Re: Location of water tank breather pipe

Which way is the one way valve? Surely I'll either be able to fill the tanks, or empty them, but not both?
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Old 02-04-2013
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Re: Location of water tank breather pipe

If you use misfits' check valve, you won't be able to completely fill your tanks.
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Re: Location of water tank breather pipe

Quote:
Originally Posted by fallard View Post
If you use misfits' check valve, you won't be able to completely fill your tanks.
It seems we are both thinking along the same lines...
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Re: Location of water tank breather pipe

You should be all set. Most tank connections for filling are at the top of the tank. The fill hose itself is something like 1 1/4", 1 1/2". The vent hose is not to bleed air out of the tank, it's so you do not create a vacuum when drawing water off the tank. If the vent hose was for bleeding air out of the tank during filling it would be the same diameter as the fill.

That's the way plumbing works, just my .02
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Re: Location of water tank breather pipe

There is only a 1/2" ID hose between the bow tank and the bilge tank. The filler is in the bow tank. I think that's why the lower tank has a vent.
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Re: Location of water tank breather pipe

The vents on my boats are at the end of 1/2" hose and the fill hose is 1 1/2". There is no check valve. They work fine with a full stream when filling. So, no, the vent hose does not have to be the same size as the fill.

If you have a check valve to keep water from overflowing your vent line when filling, then, as you fill the tank, you will trap air that becomes compressed. You will stop filling the tank when the pressure of the compressed air equals the pressure of the fill stream. This is based on observation--not conjecture--and the volume of trapped air can be significant. This is easy enough for MarkSF to verify by plugging his vent and then trying to fill the empty tank(s).

Bottom line: The vent is there to facilitate both fill and drain.

An easy fix might be extending the vent hose temporarily to drain into the galley sink when you are filling your tanks. You could coil it up the added vent hose and stow it after filling the tanks.
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Re: Location of water tank breather pipe

I like the idea of a separate hose, I'll try it!
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Re: Location of water tank breather pipe

Mark SF,

I went back thru the OP. Fallard is correct, the fashion in which your tanks are plumbed, a check valve will not work.

I wouldn't extend the vent into the bilge due to cross contamination issues.
It could be like installing a faucet for drinking water in your toilet.
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