Fresh Water Tank Vents

[jbw4]

My boat has 3 water tanks. Each tank's vent line rises to an elevated loop, then descends beneath the floorboards before disappearing under the engine (which is located under the cabin floor).
Attached is a photo of 2 of the 3 elevated loops.

The hoses on the left side of the photo come from the tanks. As you can see, one hose is connected to a copper loop which then connects to vinyl tubing. The copper loop has a small hole in the top, so it is "vented." The vinyl tubing transitions to polyethylene under the hallway and proceeds aft into the engine compartment where it terminates under the engine. It does not go all the way into the bilge.
The other vent (the one that transitions into the heavy duty hose shown) also proceeds aft under the hallway where it combines with the vent from the 3rd tank, which also has the same kind of non-vented loop, and the combined hose disappears under the engine.
Here are my questions.
1. Is there a reason why 2 of the tanks are vented through the heavy duty hose while the 3rd uses the much smaller vinyl/PEX tubing?
2. Is there any reason why the small vinyl hose is separately terminated under the engine instead of being combined with the other 2?
3. Is there anything wrong with the basic design that should be corrected?

 

[Don S/V ILLusion]

I don’t see any vented loop apparatus anywhere in the picture. If you are referring to a hole in the line as a vent, you might have a bigger question to ponder.

 

[Justin_NSA]

The zip ties are pretty cheesy. They will age and break.
The hoses should have respectable vents, not just holes.a
I don't see a need for the heavy hose. Maybe that's all that was laying around.
I don't have an answer for #2. I could be done either way of done correctly.

 

[dlochner]

There is nothing inherently wrong with this set up, however, it has a real cobbed together appearance. I assume the hose allow any overflow to drain into the bilge. The hole in the copper tubing prevents a siphon if the bilge water reaches the bottom of the vent. The different size hoses serve the same purpose. I have a similar set up on one of my tanks. A ½" ID hose goes to a loop which terminates just inside of a 1 ¼" ID hose that drains into the bilge.

If this was my boat, I'd replace the hoses and get rid of the copper pipe. So long as the end of the hose is well above the water level of the tank, the loop isn't necessary, however, the loop will keep debris, dust, and random crud from entering the hose. Below the open end of the looped hose there should be some sort of catchment device to collect any water that exits the tank from over filling. It could be a larger diameter hose that drains into the bilge, it could be a container that simply collects the water and needs to be emptied, or perhaps a trough that drains into the bilge.

A series of 1" PVC Tees glued together with a drain hose might work and look a lot neater.

 

[Peggie Hall HeadMistress]

I don't pretend to be an expert in fresh water plumbing, but I do know how a water TANK should be plumbed and vented:

A loop in water tank and fuel tank vent lines are necessary to prevent sea water contamination of fuel and water. But it should be a straight shot from the top of the loop to the tank...there's NO reason for it to go anywhere else first. Nor should there be any "vent" in the loop or anywhere else in any vent line on ANY tank.

Shields or Trident Flex PVC #148 water and sanitation hose is just fine for both waste and water tank vent lines. I wouldn't use clear water hose because any exposure to light promotes algae and other 'critter' growth in it. I would NOT tee any of 'em together.

Dave said " Below the open end of the looped hose there should be some sort of catchment device to collect any water that exits the tank from over filling."

The tank SHOULD be plumbed to send any overflow out the tank vent...there shouldn't be any need to sent it into the bilge.

--Peggie

 

[dlochner]

Shields or Trident Flex PVC #148 water and sanitation hose is just fine for both waste and water tank vent lines. I wouldn't use clear water hose because any exposure to light promotes algae and other 'critter' growth in it. I would NOT tee any of 'em together.

Just to be clear, the vent hoses should be not be connected to each other or connected to the series of Tees. There should be a gap between the hose and the tee. The tees are simply there to catch any water that might come up through the vent. The OD of the hose should be smaller than the ID of the tee. See the very amateur and crude drawing.

 

[Stu Jackson]

Dave's sketch answers the whole series of questions. The existing arrangement appears to be there only because the OP's boat doesn't have deck fittings for the tank vents, so what someone did was cobble together a way to drain the vent overflow to the bilge/under engine (whatever that means). Since that's what appears to be happening, the answers to the OP's three questions should be rather simple. Indeed, he should be able to answer them himself now, right?

 

[jbw4]

Here's a drawing that may help.
Thanks for the comments. It seems to me that (a) the vents terminate under the engine so that they can breath while any overflow is contained; (b) the loops are required because the vents terminate lower than the tanks; and (c) the different sizes of hose (and the pinhole in the copper piece) serve an anti-siphon function. There is no sunlight exposure, but the hoses and connections are pretty nasty. Sounds like the only improvement I really need to make in replacing the hoses is to remove the Tee and have each tank separately vented into the containment pan.

 

[dlochner]

View attachment 178026
Here's a drawing that may help.
Thanks for the comments. It seems to me that (a) the vents terminate under the engine so that they can breath while any overflow is contained; (b) the loops are required because the vents terminate lower than the tanks; and (c) the different sizes of hose (and the pinhole in the copper piece) serve an anti-siphon function. There is no sunlight exposure, but the hoses and connections are pretty nasty. Sounds like the only improvement I really need to make in replacing the hoses is to remove the Tee and have each tank separately vented into the containment pan.

Mostly yes, however the there must be a vent or air gap in the system higher than the tank. If the air gap is below the tank level, or if there is no air gap water can siphon out at least to the level of the vent on the tank. This might happen if the vent is on the side and boat heeled so that water can enter the vent. Unlikely, but I'd rather have my water in the tank than in the bilge.

Also if there are more convenient places to terminate the vent so any overflow goes to the bilge, you could do that. Another place water tanks are vented is into the anchor locker in a protected place so seawater doesn't enter the vent.

 

[FastOlson]

Worth noting is that most tank vents serve two purposes: Allow air back into the tank as the water is pumped out and Vent excess water somewhere non-harmful when the tank is being filled from a hose... IF the boat uses a deck fill.
Our boat has screw-out access ports on the top of the tanks, and NO deck fill fittings to worry about. There is a vent that is led up a couple feet higher than each tank, and has a small 'U' at the top to keep large bugs & dust out.
(Any qualified nit picker can argue that if our hull is rolled thru 360 degrees there would be some water escaping from that little vent.... even tho that would be the least of our problems at that point in time.)

We fill each tank by bringing in the water hose with its little ball-valve on the hose end, fill the tank, shut off the valve, and put the screw-on lid back on. Simple and 99% fool proof.
Even tho sometimes foolish, I have not spilled any water inside the boat using this scheme in 26 seasons.
Tomorrow is, of course, another day!

So, eliminate the deck fill, fill hose, and potential problem with 'overflows'.... something to consider... ?

 

[dlochner]

Worth noting is that most tank vents serve two purposes: Allow air back into the tank as the water is pumped out and Vent excess water somewhere non-harmful when the tank is being filled from a hose... IF the boat uses a deck fill.
Our boat has screw-out access ports on the top of the tanks, and NO deck fill fittings to worry about. There is a vent that is led up a couple feet higher than each tank, and has a small 'U' at the top to keep large bugs & dust out.
(Any qualified nit picker can argue that if our hull is rolled thru 360 degrees there would be some water escaping from that little vent.... even tho that would be the least of our problems at that point in time.)

We fill each tank by bringing in the water hose with its little ball-valve on the hose end, fill the tank, shut off the valve, and put the screw-on lid back on. Simple and 99% fool proof.
Even tho sometimes foolish, I have not spilled any water inside the boat using this scheme in 26 seasons.
Tomorrow is, of course, another day!

So, eliminate the deck fill, fill hose, and potential problem with 'overflows'.... something to consider... ?

I have deck fills for my water tanks, but I don't use them. Filling from the inspection ports prevents overflows and makes you take a look inside the tank every time it is filled. Put a brass shut off valve at the end of the hose to make this easier and neater.

https://www.lowes.com/pd/Yardsmith-Brass-Restricted-Flow-Water-Shut-Off/50328301

 

[FastOlson]

I have deck fills for my water tanks, but I don't use them. Filling from the inspection ports prevents overflows and makes you take a look inside the tank every time it is filled. Put a brass shut off valve at the end of the hose to make this easier and neater.

https://www.lowes.com/pd/Yardsmith-Brass-Restricted-Flow-Water-Shut-Off/50328301

Dave, that's a whole step up from my little plastic quarter-turn valve.

 

[jbw4]

Not real practical on my boat. The first tank is under the floor beneath the dinette storage lockers, the second tank is under the double berth, the third tank is under the galley floor and sink cabinet. None of the fill openings is accessible from above.

 

[Davidasailor26]

I usually just leave the hose end in the deck fill and walk away until it overflows. No need to stand there watching and waiting for it to fill up. As such I’m glad my tanks vent overboard so the overflow goes there and not the bilge.

 

[Peggie Hall HeadMistress]

Worth noting is that most tank vents serve two purposes: Allow air back into the tank as the water is pumped out and Vent excess water somewhere non-harmful when the tank is being filled from a hose...

You got that half right. ALL tank vents--water, waste and fuel--do serve two purposes, and one of 'em is to provide a source of air to replace contents as they're drawn out. But the other purpose of a vent is not to provide an escape for excess water, it's to provide an escape for air being replaced by incoming contents is the other one. When filling with a hose via an opening that's larger than the hose diameter, the unused space around the hose in that opening serves as the vent.

I usually just leave the hose end in the deck fill and walk away until it overflows. No need to stand there watching and waiting for it to fill up. As such I’m glad my tanks vent overboard so the overflow goes there and not the bilge.

I can't imagine why anyone would want to do it any other way. For one thing, the overflow out the vent rinses out the vent line.

--Peggie

 

[RoyS]

for over the side fresh water tank venting. I did not know that some fresh water tanks were vented into the bilge. Makes no sense to me. Anchor locker (with drain) also works. Get the drill.

 

[JamesG161]

I would never put water in the engine bilge, by design.

Spill a little oil or diesel and excess water overflows it to main bilge?
Jim...

 

[JamesG161]

I would connect Tank 1 and 2 in a tee and be done.

1) They will overflow to each other and vent too.
2) Tank 3 should be cut off at the top as high as you can. Avoid overfills.

No loops needed.

Jim...

 

[JamesG161]

For you guys who let your tanks over flow and not watch it...

A typical shore water hose runs about 5 gallons per minute.

Also you might use your tank level sensor.

Or hire a dock helper and use this.

Orbit 3/4 In. Plastic Water Flow Meter 56854 - Walmart.com

$17 device and sip a beer.
Jim..

 

[Davidasailor26]

For you guys who let your tanks over flow and not watch it...

A typical shore water hose runs about 5 gallons per minute.

Also you might use your tank level sensor.

Or hire a dock helper and use this.

Orbit 3/4 In. Plastic Water Flow Meter 56854 - Walmart.com

$17 device and sip a beer.
Jim..

Just to be clear, I leave mine running while I do other random things in the cockpit or around the mast. So it runs for maybe 30 seconds after it’s full. I don’t just leave it running for an hour unattended. My tank monitor reads in 25% increments, so the tank generally takes another minute or two even after the that reads full, and using that to estimate the time I’d need to fill the tank wouldn’t be too precise.