Options for water tank vents?

[Mexican Hat]

I have tried unsuccessfully to find a water tank vent that functions like the safety vents on car gas tanks. In a car this is intended to stop gas leaking out should the vehicle flip. These vents have a valve that is closed by liquid but remains open to air, allowing unmonitored filling. As the tank fills, water flows into the valve, forcing it closed, water will then back up into the fill hose and as it does it indicating that the tank is full.

As I work on installing the three water tanks in my boat the ability to have a small vent valve on the tank rather than an extended length of hose and a vented loop would make installation much easier and neater. Plus I have no way of making the vented loop higher than the deck fill.

Does anyone know if there is a small, self-contained valve suitable for water tank vents that functions like the car valves do?

[coopec43]

This is something I'll have to consider too. Is there anything here that fits the bill. (I would appreciate your comments)
https://www.boataccessoriesaustralia...s/default.aspx

Why couldn't you use one of these vents attached by food grade tube to the top of the tanks and the breather placed high up inside the yacht (as one person suggests- see below) or near the deck fill so you could see the tanks are full when it overflows. Perhaps any overflow could be plumbed into a bilge pump outlet?

There's a few threads on "water tank vents" too which I have yet to read.

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[a64pilot]

Originally Posted by Mexican Hat

I have tried unsuccessfully to find a water tank vent that functions like the safety vents on car gas tanks. In a car this is intended to stop gas leaking out should the vehicle flip. These vents have a valve that is closed by liquid but remains open to air, allowing unmonitored filling. As the tank fills, water flows into the valve, forcing it closed, water will then back up into the fill hose and as it does it indicating that the tank is full.



As I work on installing the three water tanks in my boat the ability to have a small vent valve on the tank rather than an extended length of hose and a vented loop would make installation much easier and neater. Plus I have no way of making the vented loop higher than the deck fill.



Does anyone know if there is a small, self-contained valve suitable for water tank vents that functions like the car valves do?

In a car your thinking of a roll over valve, it does the opposite of what your asking cause a roll over valve is heavy and will only close off if you turn it upside down.
However there are valves for water that do exactly what you want, they are nothing more than a ball like a ping pong ball that floats up and closes off the water flow.
Look at a wet vac for an example

Great way to over pressurize and bust your tank though, I’m sure you don’t want that, so I’m confused as to what you do want?

[Sailmonkey]

That sounds like complication for no good reason.

Why not run the vent a little ways above the tank and the. Back down. It’s just fresh water.

[Mexican Hat]

Thanks for the reply coopec43 and the other comments.

Coopec I don’t think the one’s you sent links to will work. They are regular air vents, AFAIK without a valve. I have seen those before.

Okay, so for the others who commented, to clarify: The reason why I am thinking of a valve that stops the flow of water is because I can’t see the tanks from the deck fill (cat with tanks in each hull). I need to know when they are full so I don’t pump water into the boat through the breather valve. I could do a vented loop but that requires a mess of hose and fittings in an two inconvenient locations and it still wouldn’t let me know when the the tank was full. Now sure, I can make something with a deck vent or a loop but I was hoping there was a neater and simpler solution. And BTW it's just designed for pouring water in the deck fill, so there's no risk of over pressurizing the system.

And clearly this is a real issue. There are multiple threads discussing various ways of determining when the tank is full and at least one company makes a whistle to do just that. Others have come up with systems that pipe overflow to a location visible from the fill area. All of which is fine but requires additional plumbing and complexity. A valve would seem to be simple, self-contained and effective

The thing I have in mind is like a breather valve on a motorcycle or car gas tank. Or perhaps something like the old ping-pong ball valves they used to fit in snorkels. They allow air to move freely in either direction but block the flow of liquid. While it might be a pipe dream, a valve like that on the vent fitting on the tank would be simple to install, unobtrusive and effective in comparison to the vented loop system and at the same time will give deck-level indication that the tank is full. I have looked at a variety of plumbing check valves but haven’t found anything yet. I've used flap valves on a well but they are pretty sensitive and I suspect with a vigorous flow of air they would probably close anyway.

I hoped that perhaps there was a ready made solution out there somewhere, designed for just this purpose, though not necessarily for boats

And I have read a number of threads on this topic, found by using the magical search feature...

[coopec43]

Well I've decided I won't have to worry about this as I will install a $1600 de-salinator to fill my three tanks and should be able to fit some sight tubes.


Looking at your post again wouldn't a "Float Ball Valve Shut off Automatic Fill Feed Aquarium Fish Tank Water" be a possibility?

https://www.ebay.com.au/i/273573831182?chn=ps

https://www.google.com.au/search?q=f...w=1069&bih=587

[Mexican Hat]

I had not thought of that kind of valve at all and yes, I think something like that could work, certainly gives me a whole new way of looking at the problem. Thanks.

And Im curious what desalinator costs $1600?

[a64pilot]

OK threads on determining when your tank(s) are full are usually fuel tanks.
The whistle you speak of is for a fuel tank, the Watermaker output is so small I doubt the whistle would work though.

I know when my water tank is full by when the water from the manual water pump starts flowing into the sink, nothing simpler than that.

You keep speaking of traps and vacuum breaks etc. you do understand that none of that is required? A vent is simply a hose that runs from the top of the tank to an outboard fitting, no traps, no vacuum breaks, no valves, just a smallish hose is all.

[a64pilot]

Originally Posted by Mexican Hat

And Im curious what desalinator costs $1600?

There is a guy in Fl that sells one based of of a Karcher pressure washer for about that price.

[NPCampbell]

Originally Posted by Mexican Hat

I have tried unsuccessfully to find a water tank vent that functions like the safety vents on car gas tanks. In a car this is intended to stop gas leaking out should the vehicle flip. These vents have a valve that is closed by liquid but remains open to air, allowing unmonitored filling. As the tank fills, water flows into the valve, forcing it closed, water will then back up into the fill hose and as it does it indicating that the tank is full.

As I work on installing the three water tanks in my boat the ability to have a small vent valve on the tank rather than an extended length of hose and a vented loop would make installation much easier and neater. Plus I have no way of making the vented loop higher than the deck fill.

Does anyone know if there is a small, self-contained valve suitable for water tank vents that functions like the car valves do?

Modern car gas tanks are sealed with no venting outside of the tank. Expansion is handled via a vapor line to the charcoal canister. Vacuum is handled via a one way valve in your gas cap or a vent valve. Overfilling can force liquid down the vapor line which can damage your charcoal filter.

I think what you are looking for is a normal float valve, a la toilet bowl style, rigged to the vent?

[Mexican Hat]

Thanks for all the replies. Food for thought.

Coopec, I looked up that water maker you mentioned. Looks like a pretty good deal compared to the others out there.

[Bill O]

Yes you can fill your boat up with water if you aren't paying attention to what you are doing and supposed to be monitoring. Have seen over filling happen with both water and fuel. Clearly an overfill w/water is less of a problem.

Originally Posted by a64pilot

I know when my water tank is full by when the water from the manual water pump starts flowing into the sink, nothing simpler than that.

Will agree w/A64 and others to keep it simple. Our overflow also goes into the sink and has worked well for many years.

Not sure about the concern in the initial post of keeping the water in the tanks if you flip/roll the boat. (maybe it was only an example w/the car analogy). If the boat rolls over, you'll have more to worry about than how much water remained in your tanks.


Bill O.

[thinwater]

Originally Posted by Mexican Hat

...And BTW it's just designed for pouring water in the deck fill, so there's no risk of over pressurizing the system....

Yes, there is. As soon as you screw the deck plate down it is sealed. When the hot water heater comes on, water expands. When the sun comes out, water expands. auto and chain saw tanks can take pressure and have a PR vent.

Not a huge risk, but not zero.


The simplest solution is probably a ball float vent valve (Google). Normally they are for petrol, but it would be simple to make one.

[thinwater]

BTW, the REASON the ball floats are internals is because this insures and air space, vital to avoiding over pressuring the tank. Yes, they could design them to put them in line, but that would be a bad idea and would violate the building code.

[wrwakefield]

It looks like you could easily proof the concept using a cheap vacuum breaker/vent fitting with a floating ball shut-off like this one:



If it works as needed, you are finished. If it doesn't, you aren't out of pocket more than a couple of coffees...

Our two water tanks vent into the galley sink so I haven't tried [or need] this type of vent...

Best wishes sorting it out.

Cheers! Bill