I have a Dometic vacuum toilet system with a separate holding tank. There is an overboard seacock in the system, a tank/overboard selection valve, and a Whale pump that can be used to pump the holding tank overboard. The output from the vacuum generator goes through a vented loop and then to the tank/overboard valve. Every time I flush the head a bit of ..ahem.. liquid spits out the air valve on the vented loop. I have removed and replaced the tiny duckbill air valve, and yet it still spits. This is a new boat to me and I am wondering if this system is configured correctly. Or is it just bad luck with two leaking valves?
Vented Loop Air Valve Leaking ..... The Bad Stuff
- Thread starter TThack
- Start date
Vented loops are actually anti-siphon valves..the air valve closes to allow liquid that's being PULLED through a line to pass, opens to let air into that line to break a siphon. However, what you have is anti-siphon device (vented loop) in a line through which tank contents are being PUSHED. The only thing it can do is spit 'cuz it's in the wrong place.
It's right to have a vented loop in any line connected to a below waterline thru-hull, but it should not be installed ahead of the y-valve...it belongs between the overboard discharge pump (Whale pump) and the thru-hull.
And btw...I've written a piece I call "VacuFlush 101" that explains how they work (an amazing number owners think they do, but don't) and how to prevent 99% of problems with it. I'll be glad to send it to you or anyone else who wants it if you'd like to send me a PM (private message) that includes your email address...no way to attach anything to a PM.
It's right to have a vented loop in any line connected to a below waterline thru-hull, but it should not be installed ahead of the y-valve...it belongs between the overboard discharge pump (Whale pump) and the thru-hull.
And btw...I've written a piece I call "VacuFlush 101" that explains how they work (an amazing number owners think they do, but don't) and how to prevent 99% of problems with it. I'll be glad to send it to you or anyone else who wants it if you'd like to send me a PM (private message) that includes your email address...no way to attach anything to a PM.
One of these days I'll learn not to post after a second glass of wine with dinner....I got this much right:
What I should have included but didn't: Your y-valve IS the wrong place, but I'm betting there is no air valve in it 'cuz air valves are sold separately and 90% of people don't even know they exist. An air valve in a line through which liquid is pushed wouldn't open...but if no air valve is installed in the loop, there's nothing to prevent it from squirting out the hole in the nipple at the top of it---which is where the air valve belongs--whether the loop is in the right place or not. Photo shows a vented loop with an air valve in place.
(Thanks for catching it, jv)
Attachments
Thanks for the helpful reply. I have attached a sketch of the head system layout on my boat. I do want to make it clear that there is a tiny duckbill air valve at the top of my vented loop. I removed it and cleaned it. It still leaked water. I installed a new duckbill valve and cap there. It still leaks. I hope my sketch clarifies my layout and appreciate any suggested corrections.
PS I want to be sure to state that the duckbill valve is facing the right way, with the "lips" facing into the pipe.
PS I want to be sure to state that the duckbill valve is facing the right way, with the "lips" facing into the pipe.
From your description, I THINK the problem may be that you've installed a rubber duckbill valve--which is a replaceable part IN an air valve--without the rest of the air valve. The rubber duckbill should be in a housing that either threads into the hole in the nipple or fits onto the nipple as shown in the photo I posted above. Without that housing, there's nothing to prevent waste from leaking around the valve.
Attachments
Thanks again for your help. I am going to check the installation again when I am back at the boat later today. For reference, the I ordered the cap and valve from here: https://shop.hamiltonmarine.com/products/vented-loop-cap-10599.html
and the installation looks like the attached picture from their site.
and the installation looks like the attached picture from their site.
That's the same one as in the first photo I posted. If you're sure you installed it correctly, it's possible you may have gotten a defective one. Have someone flush a whole bowlful of cleanr water while you take a close look at the vented loop to see exactly where it's leaking--squirting out the top or maybe leaking around the bottom of the cap. Then you may want to give Forespar a call: 949-858-8820
Okay, this is somewhat embarrassing, but the problem is solved. In short, the cap was simply not on tightly enough! The valve is up in an inaccessible area, so I was operating mostly by feel. There may also have been some problem with the (plastic) threads. I got another couple of turns on the cap by using additional force (more than I usually would on plastic threads) and it sealed up.
Thanks for your patience and expertise. Although this was in the end a simple solution, I wouldn't have gotten there without your help and suggestions.
Thanks for your patience and expertise. Although this was in the end a simple solution, I wouldn't have gotten there without your help and suggestions.
Sometimes the solution is SO obvious it's the last thing that would ever occur to you. Been there, done that more times than I can count.And despite the fact that there are thousands of words and phrases in the English language, no one has ever found a better way to put it than Ohhhhhhhhhhhh DUH!!! (plus a couple of expletives deleted)
Stop using anything with bleach in it, JV...bleach is highly destructive to rubber. I've never recommended anything that's "basically peppermint oil"...so what the heck is this stuff you're accusing me of recommending??
