Drain hose on anti-siphon loop valve?

[HeadedToTexas]

I am in the process of replacing the tiny vent line on my holding tank which had become clogged with bad news. Part of the replacement is dealing with the wye fitting that accepted the occasional drip from one of the anti-siphon loop valves. The new holding tank vent line will be a straight shot of 1" hose from a UniSeal in the top of the tank to a new stainless mushroom type through hull fitting. I am currently at the disassembly stage of this project.

I (finally) understand the purpose of the anti-siphon valve including the consequences of the drain hose clogging thus preventing the siphon-breaking function. Should I replace the gray fitting on the left above with one like the one on the right? Servicing the duckbill valve inside the right valve is far easier than the check valve diaphragm in the left valve, but I could easily be overlooking something. What would that be?

 

[Juliet 15]

Just curious - what was the consequence of the drain hose clogging thus preventing the siphon-breaking function?

 

[Comodave]

Not sure I am understanding what you are asking. The vent hose doesn’t have anything to do with the anti-siphon valve. The vent should just run from the top of the tank to the through hull in the side of the hull. No valves at all.

 

[O C Diver]

Without seeing the rest of your plumbing and assuming the boat manufacturer used two different siphon breaks ( the black and the gray ones), I respectfully suggest that you don't understand the difference between the two loops. My guess is that one operates with a vacuum in the system while the other operates with pressure in the system.

Without understanding why they are different, I would be hesitant to change one to the other.

Btw, the dip in the vent line under the beam needs to be avoided. I made a habit of flushing some water through the vent hose after each pumpout to avoid build up in the hose.

Ted

 

[HeadedToTexas]

I respectfully suggest that you don't understand the difference between the two loops.

That is definitely the real issue here. The anti-siphon loop valve is an air check valve allows air into a section of hose to break a siphon. The siphon can be a problem because when the pump stops that filled the hose with liquid, the siphon can begin returning water or liquid from the tank or the sea (or lake) into the boat. Definitely a mess and far worse than that when the bilge pumps finally fail or exhaust the batteries.

While I have used siphon hoses for many things over the decades, this BoatUS article educated me about the two different types of anti-siphon valves common in marine applications. Near as I can tell, they work the same way. One has a diaphragm and the other has a duckbill valve.

Both can be used without a hose that directs gas and liquid that gets past the valve as it seats. No hose means venting that small "spurt" into the engine room. A hose such as the one in my photo above directs the "spurt" into the holding tank vent line and overboard, but once that tiny wye fitting clogs with bacteria and solids, the function of the anti-siphon loop valve is defeated introducing the risk of a siphon creating real problems.

Does ABYC address anti-siphon loop valve discharge?

 

[HeadedToTexas]

Btw, the dip in the vent line under the beam needs to be avoided. I made a habit of flushing some water through the vent hose after each pumpout to avoid build up in the hose.

That dip will be gone once the new 1" vent line is installed later this winter. And I doubt the manufacturer built the boat this way because the wye is copper and looks out of place compared to fittings throughout the rest of the boat. My guess is that at some point the original black anti-siphon (like the one on the right) failed or clogged and the owner at the time simply replaced it with that gray one and cut in the wye to direct the "spurt" overboard.

 

[O C Diver]

I wasn't clear.

A siphon break that operates under pressure (in the hose) is designed to allow air into the system ( preventing siphoning) by having a check valve that is closed when the system is under pressure and opens (allowing air in) when the system stops, pressure goes away, and the system goes to vacuum. Another form of this break is to run a line from the siphon break overboard (or possibly in this case to the holding tank). In this case, there wouldn't be a check valve in the siphon break.

A siphon break that operates under vacuum is designed to allow air into the system (preventing siphoning) by either having a spring loaded valve that opens the valve when vacuum is decreased or has a very small hole where air is always entering the system. The small hole principle requires enough vacuum (by volume) from the pump to overcome the steady small stream of air bubbles entering the liquid flow. This type of siphon break might include a hose overboard or routed back to a holding tank vent line to mitigate the smell of effluent coming out of the small hole.

By now, I've probably thoroughly confused you. So this is the important part to understand:

If the siphon break is operating before the overboard discharge pump (between holding tank and pump), that siphon break is operating in a vacuum system.

If the siphon break is operating after the overboard discharge pump (between pump and seacock), that siphon break is operating in a pressure system.

Obviously, determine pressure versus vacuum before making changes to the system.

Ted

 

[HeadMistress]

Fwiw, a siphon can only start in a line through which liquid is being PULLED. Vented loops are only required in lines connected to below-waterline thru-hulls--toilet intake lines and direct discharge toilet lines to block sea water being pulled up them. A vented loop on a holding tank overboard discharge pump line can be avoided by ALWAYS keeping that seacock CLOSED except when in use. Dripping from a vented loop can be prevented by an air valve installed in the nipple on the top of the loop....they need occasional cleaning and/or replacement.

If you want your rendevous to be more than floating fraternity parties, y'all really should pool your resources to cover my travel expenses to come to one of your rendezvous to conduct a sanitation seminar...and you should be able to find local engine and marine electrical experts who'll educate and answer questions.

--Peggie

 

[HeadedToTexas]

If you want your rendevous to be more than floating fraternity parties, y'all really should pool your resources to cover my travel expenses to come to one of your rendezvous to conduct a sanitation seminar...

I'm in!

 

[rgano]

I must be missing something because I have not had anti-siphon valves associated with the waste tanks in my boats. Yes, when I had a pair of seawater flushing heads, I had anti-siphon vents between the heads and the seacocks. The macerator in my current boat is below the waterline as is the lower part of the waste tank. To drain the tank via macerator I open hull valve pump, pump, secure hull valve - job done. Last boat had the lower 1/3 of the 35-gallon waste tank below the waterline and not equipped with a macerator. A 2-inch drain line lead to a two-inch seacock, and the tank was drained underway in legal areas by opening the seacock and allowing suction to do its thing. Flushing was accomplished by slowing the boat to a stop allowing the lower portion of the tank to fill and then getting underway again, securing the seacock while moving to keep it empty. A deck pumpout line was connected to that 2-inch drain line - simple and effective.

 

[HeadMistress]

Anti-siphon valves/vented loops are only needed in lines connected to below-waterline thru-hulls. Because a true siphon can only be started in a line through which water is being pulled, vented loops in discharge lines break up water being forced up a thru-hull that shouldn't be open when the boat is underway--an effect known as "ram water." A vented loop can't prevent "ram water"...keeping toilet and holding tank thru-hulls closed except when in use is the solution.
However, this can even happen when above-waterline thru-hulls are submerged by bow wake or heeling for an extended length of time. The forward bilge pump thru-hull on one of my own boats was a bit too close to the waterline, making it necessary to use a dinghy bailer, big sponge and a bucket as part of my "closing up the boat at the end of every weekend" routine.

--Peggie

 

[Steve DAntonio]

Virtually without exception, I would avoid using remote hoses on all anti-sip[hon valve vents, it is an invitation for failure and flooding. If mounting the valve over sensitive gear can't be avoided, install a drip shield. A leaking anti-siphon valve has a message for you, 'service me'.

More here Antisiphon Valves – Editorial: “Workplace Distraction Revisited” | Steve D'Antonio Marine Consulting

 

[Steve DAntonio]

Re. Peggy's comment, the ABYC definition of "below the waterline" is anything submerged when the vessel heels 7 degrees.

 

[HeadedToTexas]

Virtually without exception, I would avoid using remote hoses on all anti-sip[hon valve vents, it is an invitation for failure and flooding. If mounting the valve over sensitive gear can't be avoided, install a drip shield. A leaking anti-siphon valve has a message for you, 'service me'.

More here Antisiphon Valves – Editorial: “Workplace Distraction Revisited” | Steve D'Antonio Marine Consulting

Excellent article, Steve. It all makes sense to me. The vent valves in my antiphon fittings have not been changed in many years. I am grateful I got away with it and will have them changed and the remote hose removed before we splash in the Spring. Thank you.

 

[SteveK]

Re. Peggy's comment, the ABYC definition of "below the waterline" is anything submerged when the vessel heels 7 degrees.

Is there an estimate of a measurement of how much above the standing waterline?

 

[HeadedToTexas]

Some clarity from today's mission to the boat. The discussion above has made it clear to me that I should remove the vent hose on the macerator discharge antisiphon valve. I am in the Great Lakes and may not use the macerator for years. The seacock remains closed at all times. I will either replace the antisiphon valve with a model that has no vent hose, or simply remove the vent hose. That really address the issue of this thread, but the process has created a new issue or question.

The "other" antisiphon valve in the photo above has what I would call an inlet coming from aft of the photo and a discharge leading forward from the photo. I suspect it is the washdown pump line. The washdown pump pumps raw water from a seacock to the hose fitting at the bow. Based on the conversation here, I don't see why that would need an antisiphon valve.

It may be the raw water head flush pump which also comes from a seacock and supplies the forward head on the other side of the bulkhead shown in the photo. That's a more clear application for an antisiphon valve, but I have yet to find a corresponding antisiphon valve for the raw water flush pump on the aft head.

For what it's worth, neither air conditioner pump has an antisiphon valve despite pulling water from a submerged through hull and discharging water to a through hull very near the water line that could easily be submerged at times.

 

[HeadedToTexas]

In a moment of weakness, I failed to get close up photos of the fittings themselves that may have revealed manufacturer and model numbers. Based on image searches, I think I have Vetus and Onan antisiphon valves. My Google-Fu may be weak, but I am not finding replacement duckbill inserts for these two fittings. Any thoughts?

 

[rgano]

I can think of no reason to have an anti-siphon valve on a wash-down pump or an air conditioner. Anytime there is potential for flooding or water injestion into machinery - yes.

 

[O C Diver]

Some clarity from today's mission to the boat. The discussion above has made it clear to me that I should remove the vent hose on the macerator discharge antisiphon valve. I am in the Great Lakes and may not use the macerator for years. The seacock remains closed at all times. I will either replace the antisiphon valve with a model that has no vent hose, or simply remove the vent hose. That really address the issue of this thread, but the process has created a new issue or question.

View attachment 161126

The "other" antisiphon valve in the photo above has what I would call an inlet coming from aft of the photo and a discharge leading forward from the photo. I suspect it is the washdown pump line. The washdown pump pumps raw water from a seacock to the hose fitting at the bow. Based on the conversation here, I don't see why that would need an antisiphon valve.

It may be the raw water head flush pump which also comes from a seacock and supplies the forward head on the other side of the bulkhead shown in the photo. That's a more clear application for an antisiphon valve, but I have yet to find a corresponding antisiphon valve for the raw water flush pump on the aft head.

For what it's worth, neither air conditioner pump has an antisiphon valve despite pulling water from a submerged through hull and discharging water to a through hull very near the water line that could easily be submerged at times.

I wouldn't remove an anti siphon valve on a boat without being absolutely certain where it went (head or washdown pump) and why the builder installed it to start with.

Ted

 

[HeadedToTexas]

I definitely will not be removing either antisiphon valve, but I do plan to remove the hose that goes from the macerator antisiphon valve to a wye fitting that used to be in the holding tank vent line. I'm sure the intent was to divert any stink burps from the macerator line into the holding tank vent, but I am fine suffering the consequences of any stink burps should I ever start using the macerator.

And I expect to eventually figure out what the thinner, dark antisiphon valve serves. It's just a matter of feeling limber enough to chase down the hoses. An assistant will help too and I was working alone yesterday.

 

[HeadedToTexas]

Found it. It's made by Forespar, not Onan. Not cheap, but what is these days? Forespar MF 841 Vent Cap Assembly from Amazon.

 

[HeadMistress]

I definitely will not be removing either antisiphon valve, but I do plan to remove the hose that goes from the macerator antisiphon valve to a wye fitting that used to be in the holding tank vent line. I'm sure the intent was to divert any stink burps from the macerator line into the holding tank vent, but I am fine suffering the consequences of any stink burps should I ever start using the macerator.

A drain line on a vented loop is a very bad idea...the nipple on the top of the loop will only allow a 1/4" hose which quickly becomes clogged with sea water minerals and anything else that goes through the loop, turning the loop into an UNvented loop that no longer has any ability to prevent/break a siphon. An air valve (almost always sold separately from the vented loop) is the correct solution. Teeing or wying anything into the holding vent line is also a bad idea because whatever goes through whatever is teed into it can block the vent line.

--Peggie

 

[Greg QS]

To answer your questions
1 yes leave anti siphon valve on macerator line unless deleing the macerator. It prevents you from filling your waste tank with sea water when you turn off the macerator. Your tank is lower that the discharge point.
2 yes you can use the easier to service vented loop.


Vented loops porpoise either water or raw water vent.
Simply stops the possibility of draining the associated tank from siphoning out the vent line or from sucking water back through the discharge line that is below the water line and re filling the tank.

 

[Greg QS]

maybe this will help

 

[HeadedToTexas]

Yesterday I confirmed that the "other" antisiphon vented loop (the starboard one with the black fitting) is in the line feeding raw water to the forward head. Since the aft head and washdown pump all draw raw water from the same through hull fitting, that one antisiphon vented loop serves all three lines. Just an update.

 

[HeadMistress]

Only one thing wrong with your logic: The intake vented loop doesn't belong in the line between the thru-hull and the pump because it would interfere with the pump's ability to prime. On manual toilets it belongs between the pump and the bowl and needs to be at least 6-8" above the boat's waterline (which means putting it under a vanity renders it useless in a below-waterline head), which requires replacing the short line that toilet mfrs use with one long enough to do that.

It CAN go in the line between the thru-hull and pump-motor assembly in a seawater electric toilet that doesn't use a remote intake pump...I always liked to put it between the pump-motor assembly and bowl because that protects it from any not-so micro sealife that can be pulled in, but you aren't likely to find that option in any of the toilet installation instructions.
Most fresh water electric toilets have a solenoid valve somewhere in the intake that almost always includes a vented loop.

An intake vented loop isn't needed in above-waterline toilets, also making one unnecessary in the intake line to washdown pump.

--Peggie

 

[HeadedToTexas]

Vague phrasing on my part, Peggie. The vented loop is definitely between the pump and the head. Thank you.