How to test vented loops

[dmksails]

Probably obvious, but how do you test a vented loop to see if it's plugged?

[skipmac]

Blow in it.

[skipmac]

In case this part isn't obvious, if the vented loop is on the head discharge I would connect a hose to the loop and blow into the hose.

[model 10]

Are thinking about the little valve in the vented loop? You can take it out and inspect it.

[peghall]

Originally Posted by Guy

Are thinking about the little valve in the vented loop? You can take it out and inspect it.

And clean it while it's out...or, if it's got some age on it, replace it.

If there's a vent line on the top of the loop instead of a valve, you can bet the farm that the line is blocked at the connection. Remove the vent line and replace it with an air valve.

[Cheechako]

Yes, just clean the valve. Based on my experience with vented loops with a valve in salt water or head discharge, most are not working most the time.

[skipmac]

Originally Posted by peghall

And clean it while it's out...or, if it's got some age on it, replace it.

If there's a vent line on the top of the loop instead of a valve, you can bet the farm that the line is blocked at the connection. Remove the vent line and replace it with an air valve.

Hi Peg,

I thought I understood vented loops but now I'm a bit confused. By air valve do you mean the little gadget at the top of the loop that has a little diaphragm inside and is a one way valve, similar to a flapper valve but the circular diaphragm is attached in the center of the circle with vent holes around the perimeter?

I thought all vented loops had that or something like it that close when pressure is inside the loop but vent air into the loop when the pressure is released so prevent siphoning. At least all of them I've dealt with work this way.

Some do have a hose barb on the end as well and, since most of them drip a bit, depending on the location of the loop I'll put a hose on the barb and run the drip away from sensitive spots like wiring, equipment, etc.

So is there some different kind of vented loop without an air valve or do I misunderstand what an air valve is?

[skipmac]

Originally Posted by Cheechako

Yes, just clean the valve. Based on my experience with vented loops with a valve in salt water or head discharge, most are not working most the time.

Same experience here.

[peghall]

By air valve do you mean the little gadget at the top of the loop that has a little diaphragm inside and is a one way valve, similar to a flapper valve but the circular diaphragm is attached in the center of the circle with vent holes around the perimeter?

Yup...that's what an air valve is...and they do require a little maintenance and replacement when the diaphragm in 'em wears out. Most PVC vented loops don't have an integral air valve, they have just a little nipple on top that the air valve threads into. (see photo for an example) Because air valves are replaceable, they're almost always sold separately...which means that neither the puppies who now work in marine stores know they exist, nor do 90% of owners who are buying vented loops because the installation instructions told 'em they needed 'em.

They don't leak when instilled with a valve that works the way it's supposed to work--closed when liquid is being PUSHED through the loop, open when liquid is being PULLED through it. But they do when installed without one...and because owners don't know they need a valve, they put a line on 'em that they tee into the holding tank vent line or even install a thru-hull for 'em. But that line is so small--only 1/4"--that it very quickly becomes clogged at the loop with salt, sea water minerals--and if in a toilet discharge line--waste...turning the loop into an UNvented loop that no longer has any ability to break a siphon. Because the hose solved the drip/squirt problem, it's "out of sight-out of mind" so it's rarely if ever cleaned. In fact OP to this thread is the first person I've ever seen or heard even ask if the loop is still working.

[model 10]

Originally Posted by skipmac

Hi Peg,

I thought I understood vented loops but now I'm a bit confused. loop I
So is there some different kind of vented loop without an air valve or do I misunderstand what an air valve is?

It's just like a tiny joker valve.

[skipmac]

Originally Posted by peghall

By air valve do you mean the little gadget at the top of the loop that has a little diaphragm inside and is a one way valve, similar to a flapper valve but the circular diaphragm is attached in the center of the circle with vent holes around the perimeter?

Yup...that's what an air valve is. Most PVC vented loops don't have an integral air valve, they have just a little nipple on top that the air valve threads into. Because air valves are replaceable, they're almost always sold separately...which means that neither the puppies who now work in marine stores know they exist, nor do 90% of owners who are buying vented loops because the installation instructions told 'em they needed 'em.

They don't leak when instilled with a valve that works the way it's supposed to work--closed when liquid is being PUSHED through the loop, open when liquid is being PULLED through it. But they do when installed without one...and because owners don't know they need a valve, they put a line on 'em that they tee into the holding tank vent line or even install a thru-hull for 'em. But that line is so small--only 1/4"--that it very quickly becomes clogged at the loop with salt, sea water minerals--and if in a toilet discharge line--waste...turning the loop into an UNvented loop that no longer has any ability to break a siphon. Because the hose solved the drip/squirt problem, it's "out of sight-out of mind" so it's rarely if ever cleaned. In fact OP to this thread is the first person I've ever seen or heard even ask if the loop is still working.

People have a vented loop and don't know that an air valve goes in the top and just leave a hole there???? Once again I have been surprised at what seems to be a common lack of knowledge of basic boat systems.

The vented loop in the raw water cooling hose in my boat I have cleaned and replaced the air valve repeatedly and it always drips a little. It's a bronze Groco loop and I've found most Groco products to be reasonably well designed and manufactured. The problem is the only practical place to mount the loop is over the back of the engine and the PO just let it drip, resulting a huge rust problem. If there's a trick I haven't tried for preventing a drip or a better brand loop I'm all ears.

[Cheechako]

To me the best case scenario is a hose barb on top of the loop, for the biggest hose possible 3/8 or even 1/2 maybe, then the joker valve a couple feet, or more, above that. I would think that would keep it operational longer. :>)
Some have an enclosed valve, some have a rubber disc, some have a brass and rubber disc.

[skipmac]

Originally Posted by Cheechako

To me the best case scenario is a hose barb on top of the loop, for the biggest hose possible 3/8 or even 1/2 maybe, then the joker valve a couple feet, or more, above that. I would think that would keep it operational longer. :>)
Some have an enclosed valve, some have a rubber disc, some have a brass and rubber disc.

That sounds like a worthwhile modification to investigate. The nice, bronze Groco vented loop in my raw water line has a tiny little rubber disk. Haven't looked at it recently but as I recall it's only 1/2-3/4" diameter so not hard to get just a little salt crystal or piece of trash in the seating area to allow a leak.

What I've done so far is keep the valve as clean as possible but also run a drain hose to the bilge to reroute the inevitable leaks.