Vented loop valve

[LostAtB]

I replaced the hoses for my toilet and have a couple of questions about the valve for the vented loop. I haven't been able to find the style of valve that I have on the internet and I'm wondering if it is even the appropriate thing. The airflow seems way too small to break any kind of siphon. I assumed it was plugged up so I took it apart. Everything looks clean and intact, but the design really doesn't seem like it provides enough flow. So I guess my question is: Is this actually an anti-siphon vent or just something that fit the hole?

Thanks

[Lepke]

It doesn't take a lot of airflow to break siphon. It works because it's easier to draw in air than move liquid. Once the siphon is gone, the weight of liquid draws in air and slowly drains the line.

[peghall]

The air valve in a vented loop isn't what breaks a siphon. The air valve in a toilet intake only closes to allow the toilet to pull in flush water, opens when pumping stops to allow the air into the loop that breaks the siphon started by priming the pump. Any air valve that can be threaded into the nipple on the top of loop will work.

Intake vented loop should NOT be installed between the thru-hull and the pump...it belongs between the pump and the bowl and needs to be at least 6-8" above waterline AT ANY ANGLE OF HEEL--not just when the boat's at rest, which on most sailboats puts it 2-3 FEET above the bowl and requires replacing the short piece of hose the toilet mfr used to connect 'em with a couple of pieces of 3/4' hose long enough to reach that high. Every manual toilet owners manual includes a drawing showing the correct location...Figure 1 on the right side of page 3 in the Jabsco owners manual is a good example Jabsco Manual Twist & Lock owners manual

I've uploaded a drawing of a vented loop with air valve and a photo showing a common installation of both intake and discharge vented loops.


--Peggie

[LostAtB]

Hi Peggie,

Thank you for such a thorough reply. I suppose I should have been more clear- I have a freshwater toilet and this loop is on the overboard discharge hose after the electric pump. It seems like there should be something to break the siphon in this loop in case of the hose breaking off at the pump while it's running or failure of the valve in the pump or who know what else. It's hard to imagine a valve that I can barely blow through serving this purpose. Am I thinking about this wrong?

Thanks!

[peghall]

It seems like there should be something to break the siphon in this loop in case of the hose breaking off at the pump while it's running or failure of the valve in the pump or who know what else. It's hard to imagine a valve that I can barely blow through serving this purpose. Am I thinking about this wrong?

Yep, you are...but at least you're thinking, which more than a lot of people do. But you're waaay OVER thinking it. You're not supposed to be able to blow through it.

The odds of a hose that isn't so old it's already starting to crack an split breaking are astronomical. Air valve failure is common...it's due to failure to clean or replace as needed (clean every year as part of spring recommissioning, replace when the li'l diaphragm in looks damaged). It's not a catastrophe in a toilet discharge line, just a minor inconvenience. It'll most likely just squirt if the air valve has failed.

And btw, it's not necessary to replace the air valve with one that's identical to the one you have...any that you can thread into the nipple at the top of the loop will be fine.



--Peggie

[LostAtB]

Sounds good. Thanks again for the info and also for the reality check!