Inside vent for fresh water problem

[ontherocks83]

I need some advice or recommendations for my fresh water system. The original air vent for the fresh water system had a hose that attached to a stanchion and vented through that onto the deck. When I was doing my refit I filled in the stanchion and moved the vent to inside the cabin. I attached a check valve to the end of the hose, but didn't think that it doesn't allow air out when I am filling the tanks so they become pressurized.

Does anyone know of a check valve that will prevent water from going out, but will allow air in and out both directions?

 

[Justin_NSA]

Are you sure it's a sound idea to vent in the cabin? Am I the only one that has overfilled the tank causing water to come out the vent? I was glad it went overboard.
I don't t think you'll find a valve that can distinguish between air and water wanting to get o out.
maybe I'm not understanding the plan.

 

[ontherocks83]

no you're understanding it, in theory I wanted it inside so salt and or rain water didn't get into my tanks because I want to be able to drink out of them. I just wasn't thinking that it would stop air also.

 

[Justin_NSA]

Mine is a thru hull with a clamshell hood. That and a loop should work

 

[Ralph Johnstone]

I wanted it inside so salt and or rain water didn't get into my tanks because

Having the vent opening mounted on the hull with an internal loop to the height of the deck will accomplish exactly the same thing ....................... unless you're sinking.

Am I the only one that has overfilled the tank causing water to come out the vent?

Nah, you're waaaaaaaaay down the list for that honour .

 

[ontherocks83]

Mine is a thru hull with a clamshell hood. That and a loop should work

I can't seem to find a thru hull with a clam shell. Do they come as one piece or is it something you screw into the hull over the thru hull?

 

[Justin_NSA]

I can't seem to find a thru hull with a clam shell. Do they come as one piece or is it something you screw into the hull over the thru hull?

I just replaced the similar clamshell setup on my holding tank vent line with an 'open' thru hull fitting. I might still have it. The clamshell was part of the fitting. No need for more screw holes.

 

[ontherocks83]

I just replaced the similar clamshell setup on my holding tank vent line with an 'open' thru hull fitting. I might still have it. The clamshell was part of the fitting. No need for more screw holes.

Do you remember where you bought it from?

 

[Capt jgw]

I've seen several boats that vented the water tanks inside the cabin, but the end of the vent hose was considerably higher than the fill point. My 8.7 Columbia was that way and the end of the vent hose was inside a false bulkhead over the dinette table, just under the cabin top. Theoretically high enough to not vent water, but one of the first times I filled the tank I "let r rip", and sure enough, water all over the table. The Admiral was not amused. I didn't even know the vent was in there. From then on I ran the water more slowly and didn't have any more problems. It can work, but the vent must be much higher than the fill and you need to fill slowly. I don't think check valve would work, but there is a whistle device you can put in the line that makes noise when air passes through it. When the whistle stops, you turn off the water. They're made for fuel tanks but would work for water too.

 

[Justin_NSA]

Do you remember where you bought it from?

I try to record all my boat purchases, depressing sometimes, but I missed this part. I imagine any major retailer would have them.

 

[ontherocks83]

I try to record all my boat purchases, depressing sometimes, but I missed this part. I imagine any major retailer would have them.

Ya I started doing that with a spread sheet at the beginning of my refit, but after a short while I started getting depressed at the number and put a stop to that real quick.

 

[Ralph Johnstone]

Do they come as one piece or is it something you screw into the hull over the thru hull?

They come in both flavours. I don't bother with a clam shell as the internal loop is high enough as it should take care of any waves slamming into the bow.

 

[dlochner]

The vent serves 2 purposes to let air out while filling the tank and to let air in while using water in the tank.

It can be vented inside the boat, however to do this correctly the vent needs to let any overfill flow into the bilge, it needs to prevent bilge water from entering the vent, and it needs to prevent water in the tank from draining when the boat is heeled.

One way to do this is to have the vent loop up above the height of the tank regardless of heel so it does not drain and end at a height above the tank. The open end of the vent is placed directly above a larger diameter hose which leads any over flow to the bilge. No connector is used between the small vent hose and the drain hose, this provides a vacuum break to prevent siphoning.

 

[Peggie Hall HeadMistress]

I've been reading all the posts and finally decided it's time for me to offer some advice:

Catalina vents all tanks--fuel, water and waste--into rail stanchions to keep sea water out 'em. It's a brilliant way to vent fuel and water tanks because the slits/holes in the stanchions are on the AFT side of it...so even if your rails are in the water, sea water runs aftward over the front of the stanchion...it doesn't get into the vent.

So my advice: drill, scrape, whatever you need to do, to remove whatever you used to fill the openings in the stanchion and restore the vent line to it. If you must have a "belt and suspenders" put an arch in the vent line--or run a foot of it a few degrees uphill if there's no room for a arch-- before it goes down to the tank. Salt, dust, pollen can build up and clog the holes in the stanchion, so run a screwdriver blade, ice pick, whatever works to clean 'em out regularly as PREVENTIVE maintenance.

Btw...although venting fuel and water tank vents into a rail stanchion is a great idea, venting a holding tank into a stanchion is anything BUT even a decent idea. What to do about that is a topic for another thread.

--Peggie

 

[Ron20324]

The REAL vents are made for such, and they have screens to keep the wildlife out. Yeah, the screen can become clogged, but it's less trouble than getting stink bugs- or whatever else you have- out of the entire hose- and STILL push them down into your water supply!

 

[JamesG161]

Does anyone know of a check valve that will prevent water from going out, but will allow air in and out both directions?

Yes.
Dorade box - Wikipedia
Common use on Sailboats.
Jim...

PS: The concept works for your water tank vent.

 

[TomY]

The vent serves 2 purposes to let air out while filling the tank and to let air in while using water in the tank.

It can be vented inside the boat, however to do this correctly the vent needs to let any overfill flow into the bilge, it needs to prevent bilge water from entering the vent, and it needs to prevent water in the tank from draining when the boat is heeled.

One way to do this is to have the vent loop up above the height of the tank regardless of heel so it does not drain and end at a height above the tank. The open end of the vent is placed directly above a larger diameter hose which leads any over flow to the bilge. No connector is used between the small vent hose and the drain hose, this provides a vacuum break to prevent siphoning.

This was standard practice when the built my boat in 1961. The tops of the water tanks (3) are at bunk/settee level. The vents, copper tubing, run behind the ceilings up to deck level and have a 180-degree bend just below the decks.

If you overfill the tanks, freshwater simply goes into the bilge. The hull is designed to direct any water into the bilge (aren't all hulls?).

In practice, I can easily hear the change in flow when the 40-gallon tanks are reaching the top. If you miss that, the hose starts blasting water out of the deck fill pipes, but the vents are 1/2" so volume is minimal.

If you bury the rail sailing after filling the tanks, you could get a bit of FW through the vent that flows into the deep bilge.

 

[dlochner]

The REAL vents are made for such, and they have screens to keep the wildlife out. Yeah, the screen can become clogged, but it's less trouble than getting stink bugs- or whatever else you have- out of the entire hose- and STILL push them down into your water supply!

The mud wasps I watched crawling in to the fuel vent yesterday didn't seem to notice the screen. Or maybe one of them installed hinges on the screen door.

 

[Justin_NSA]

The REAL vents are made for such, and they have screens to keep the wildlife out. Yeah, the screen can become clogged, but it's less trouble than getting stink bugs- or whatever else you have- out of the entire hose- and STILL push them down into your water supply!

I added one of these in my vent line to trap insects. Read it in Practical Sailor.

 

[jviss]

My 1984 Catalina 36's water tanks were vented into the cockpit, the inside side wall, starboard side, just above the cockpit scupper. I thought that was a good idea.

My Tartan 3800's tanks are vented via a high loop of hose into the bilge. The fuel and waste tanks are vented via through-hull vents, in the topsides just below the toe rail.

You can get a valve that vents air and not water, it's called an air vent, and is used on hydronic heating systems. Homeowner and hardware stores have them, and they are relatively cheap. However, I wouldn't recommend this as once it closes you risk pressurizing the tank, and could break something.