Why are vented loops vented outside?

[BobHorn]

The vent on a vented loop is to allow air in, there should not be any flow out. So why the outside venting? What am I missing?


Bob

[slug]

They alway leak or bleed exhaust fumes

Some styles have no valve

A classic vent overboard location is to use the cockpit drain

Plumb into the cockpit drain high up near the cockpit sole

Avoid any vent location that can pipe exhaust into the boat

[Chotu]

Originally Posted by slug

They alway leak or bleed exhaust fumes

Some styles have no valve

A classic vent overboard location is to use the cockpit drain

Plumb into the cockpit drain high up near the cockpit sole

Avoid any vent location that can pipe exhaust into the boat

Especially the black water vented loop. Ha ha ha. Always the first to leak.

[deblen]

https://www.boatus.com/magazine/2018...hon-valves.asp

[slug]

Black water vents need to be vented out at waterline level.. typically in the boot stripe

Both port and stb side via a tee to be certain the the vent can breath with on a tack

Aft is best ... only swimmers smell the charter sauce

[BobHorn]

Exhaust vent does go into a cockpit drain, easy to see if water is flowing. I guess the only reason to vent the black water vent is in case of the joker valve failing.

[peghall]

Vented loops allow air into a line through which liquid is being PULLED...when installed in a line through which liquid is being PUSHED, liquid is squirted out the vent. Which is why an air valve should be installed in the nipple at the top of the loop. Because those are replaceable items, they're rarely included with the loops, so many people don't even know they exist. To deal with the squirting, they put a vent line on the nipple, which is a bad idea 'cuz the line is usually only 1/4" and quickly gets clogged by sea water minerals and whatever else passes through it, turning the loop into an UNvented loop that no longer has any ability to prevent a siphon. Because the hose solved the squirting problem, it's become "out of sight/out of mind" and is never removed from the loop and cleaned out.


An air valve in the loop in a toilet intake line is equally important because without it, air can be pulled in through the hole in the nipple, preventing the toilet from priming.



--Peggie

[peghall]

Joker valves don't have to fail to leak...even a slightly worn one will. But joker valve is not a siphon break...that's what a vented loop does...and the reason why they're only needed in lines that are connected to below-waterline thru-hulls.


--Peggie

[hpeer]

Originally Posted by peghall

Vented loops allow air into a line through which liquid is being PULLED...when installed in a line through which liquid is being PUSHED, liquid is squirted out the vent. Which is why an air valve should be installed in the nipple at the top of the loop. Because those are replaceable items, they're rarely included with the loops, so many people don't even know they exist. To deal with the squirting, they put a vent line on the nipple, which is a bad idea 'cuz the line is usually only 1/4" and quickly gets clogged by sea water minerals and whatever else passes through it, turning the loop into an UNvented loop that no longer has any ability to prevent a siphon. Because the hose solved the squirting problem, it's become "out of sight/out of mind" and is never removed from the loop and cleaned out.


An air valve in the loop in a toilet intake line is equally important because without it, air can be pulled in through the hole in the nipple, preventing the toilet from priming.



--Peggie

Peggie,

I’m being a bit dense here. Can you point me to some visual aid, maybe a exploded parts diagram to see what you are talking about.

We have vented loops on toilet in and out Lines (Lavac). I clean them when I can’t hear them anymore. No vented lines. No signs of mess after 10 years. No noticeable smell.

[peghall]

Your system obviously ain't broke so I wouldn't even think trying to fix it!
In response to your request, I've upload a photo of a PVC vented loop with an air valve.

--Peggie

[Hudson Force]

I'm not sure of the intended meaning of the term "Outside" in the thread title. My most reasonable thought is that the vented loop is allowing air to enter from "outside" of a closed system in order to break a siphon flow. Examples of this may be with the engine water cooling that prevents the exhausting cooling water from siphoning back into the engine by allowing air to enter from "outside" the system. Another example may be with the effluent line from a bilge pump when the exit is close to the water line. The air entering this siphon break would prevent water returning into the vessel if the boat is low in the water or taking in sips of water with each rock in at a rocking mooring. Due to this I was not considering that the term "outside" in the thread title was meaning outside of the vessel. I have had open vents from holding tanks, but never with anti-siphon valves. Well-maintained anti-siphon loops do not give off liquids or gasses to the outside of theses systems. I don't recall ever seeing an anti-siphon loop on the exterior of a vessel, but they must exist in some cases.

[pcmm]

Originally Posted by slug

Black water vents need to be vented out at waterline level.. typically in the boot stripe

Both port and stb side via a tee to be certain the the vent can breath with on a tack

Aft is best ... only swimmers smell the charter sauce

That's not necessarily true. black water vents are almost always situated at the sheerline or the coaming ( that is grose!) but in all my boating I have never seen a blackwater vent at the waterline level. its almost universally close to the sheerline.

[noelex 77]

A potential syphon situation is common in many marine plumbing installations from the raw water cooling the engine to the toilet. Vented loops are fitted to break this syphon.

The biggest problem is the syphon action is very counterintuitive. Water travels for part of its journey uphill without any pump or energy input, almost by magic. It is very hard to imagine this would be possible. Thus the need for a syphon break is not obvious.

Seeing is believing. Use some hose to deliberately create a syphon. It can be a practical way of transferring liquids such as fresh water and fuel.

[slug]

Originally Posted by pcmm

That's not necessarily true. black water vents are almost always situated at the sheerline or the coaming ( that is grose!) but in all my boating I have never seen a blackwater vent at the waterline level. its almost universally close to the sheerline.

You can sheer mount

They just stink every time the toilet is flushed

[peghall]

Are y'all referring to vented loops or holding tank vents? There shouldn't be any odor or anything else from a vented loop that has an air valve installed. And nothing out of one that's been "vented" via a hose if it's been longer than about 6 months since the hose was attached because the hose has become clogged by whatever squirts out of nipple on the top of the loop.


--Peggie