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deniseO30 06-21-2013 09:53 AM

fresh water tank vent
I have this somewhat annoying little problem with the fresh water tank vent in my boat. :rolleyes:

The line is clear 5/8" ID. So, when filling the tank I take the line off and whoosh.. the air comes rushing out as the tank fills.

I can blow air out the line. when it's on the tank outlet (that's not restricted either) and I fill the tank, pressure builds and makes the tank swell because the vent isn't relieving the air.

The actual vent is a good 4ft fwd and 3ft up the head bulkhead to just under the rub rail. I can only guess it's too long, but it doesn't make any sense that just air can't flow freely in the vent tube.

Apparently this problem was the cause for the poly tank to crack (we repaired it with with 3m "scotchweld" for polyethylene when I first got the boat. I don't think the PO was aware of it.

norahs arc 06-21-2013 10:03 AM

Re: fresh water tank vent
Can you blow air through the line from the tank end when it is off the tank? If not try pushing a smaller diameter line through to check for foreign material in the line. I have heard of insects nesting in the vent lines and blocking them.
If you can blow through the line from the tank end when off I don't know what could stop air flow unless when it is connected it gets kinked.
Good luck.

deniseO30 06-21-2013 10:17 AM

Re: fresh water tank vent
It's a minor mystery for sure Noahs. I think bugs or cobwebs.

travlin-easy 06-21-2013 10:56 AM

Re: fresh water tank vent
Denise, if the vent line had a goose-neck in it, it may have had water in it, which would cause a back pressure. And, if the end of the vent was not covered with a filter screen, mud daubers love to make a nest in those small openings. I found this out the hard way with the vent for my holding tank, which darned near exploded because of the mud plug that was constantly being replaced by the wasp.

Good Luck,

Gary :cool:

pdqaltair 06-21-2013 11:05 AM

Re: fresh water tank vent
Either plugged or kinked. You simply can't load water fast enough to overwhelm a 5/8-inch line of any possible length. I doubt a water trap could cause enough back pressure to matter, but that of course depends on how much water is trapped.

I STRONGLY dislike clear vinyl hose because of its tendency to kink over time; though it looked fine when installed, over 6 months it slowly goes flat.

If you find a kink, try 5/8-inch sanitary line; it will last forever in this application.

deniseO30 06-21-2013 11:50 AM

Re: fresh water tank vent
It's been that way from day one LOL guess I'll tackle it again this weekend. Thanks Gents!

chef2sail 06-21-2013 12:02 PM

Re: fresh water tank vent
Redo the whole vent line with cheaper sanitary line as it wont kink. Connect to the tank but leave the other end free and do not connect. Fill tank with water and see if that solves the problem before fixing the open end permanently un the bulkhead space. It May be that the line is too long and too far above the water line.


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