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Old 16-06-2021, 05:19   #1
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Marine Sink Check Valves

All three of the sinks (two heads and galley) on our Tayana 47 discharge below waterline and are fitted with swing check valves, presumably to eliminate the "fountain effect" in heavy going.

These check valves are close coupled to the sea cock and predictably, are totally frozen in place mid swing by marine growth/ calcium buildup. This particular seacock was frozen and I broke the handle off resulting in the whole assembly needing to be removed from the boat. It was actually doing it's job because it let the sink drain well enough but blocked the line enough to stop a fountain.

Questions: Are check valves on marine sinks typical and needed? A search brought up very little on the topic. I'm wondering because my usual sources (Defender, Hamilton, Jamestown) do not carry or list what I think is the needed, modern replacement. They have the Groco PNC-1000 (0.45psi opening pressure) but I think I need/want the CV-100 (0.19psi opening pressure). The bottom of the sink is probably 2.5/ 3 feet above the seacock if I had to guess.

What is the standard configuration to solve this problem? Shouldn't the check valve be above the waterline so it does not see marine fouling?

As a side note, to get the thru hull out I took a grinder to the outside mushroom and ground it off. The heat softened the sealant and a few blows of a hammer pushed the the whole assembly into the interior. Way easier than than the alternative for a thru hull I knew I was gong to replace adn located in a very tight spot. In doing this I found that the hose to check valve connection was made with a threaded nipple instead of a proper hose barb fitting. The nipple sheared off flush with the check valve with very minimal force and I found the metal to be highly degraded. It lasted nearly 30 years so I don't think it was brass but either way it was a boat sinking waiting to happen. Pretty scary.
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Old 16-06-2021, 05:31   #2
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Re: Marine Sink Check Valves

The thruhull and seacock are typically two seperate things joined together - why you had to remove the thruhull is questionable but regardless, you don't need check valves on the sink lines.


The stuff which goes down sink drains can easily clog any valve making it useless unless maintained frequently which is more work for less value.


Simply closing the seacocks while underway if you are worried about backflow is actually preferable as that makes you exercise the seacocks which, if you had done that prior, would likely have eliminated the first problem you had.
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Old 16-06-2021, 05:36   #3
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Re: Marine Sink Check Valves

Our vanity sink bottom is roughly 8-10” above the waterline in the forward third of the boat. The discharge is below the waterline facing down angled outboard at about a 25 deg angle.

We’ve been in some fairly gnarly stuff and never had water re-appear in this sink.
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Old 16-06-2021, 05:46   #4
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Re: Marine Sink Check Valves

Many newer boats have the sinks drain into a sump where the water is then pumped overboard well above the waterline.


If you do use a check valve, look at the membrane sink traps. Hepvo was the pioneer, there are now imitators. They are less likely to clog, and because they do not require as much operating pressure to open that an angle check does they can be installed at the sink where they are easier to maintain.
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Old 16-06-2021, 06:38   #5
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Re: Marine Sink Check Valves

Agree w/the other responses, no need for check valves for the sink drains. If you have any excessive gurgling or water backing up into the sink, simply close the valve (should be easily accessible).

If one thru hull was questionable, would be a good idea to check your other thru hulls if they are all 30 yrs old.
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Old 16-06-2021, 06:52   #6
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Re: Marine Sink Check Valves

First comment: Swing check valves are not designed to work on downward flow, since they count on gravity to pull them closed. It is possible they NEVER worked.

I have never seen a boat where they were actually needed. No “fountain effect.” Your best bet is to talk with other Tatyana owners and see what they say. My bet: a bad idea, badly implemented.
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Old 16-06-2021, 09:14   #7
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Re: Marine Sink Check Valves

Following. Our 1989 TASWELL has the same setup....a horizontal "gravity" swing-valve just before the 90* ell and thru-hull. We've often had the sink stop up/fail to drain, and we carry an old-fashioned plunger.....which so far has always done the job. We did replace all our thru-hulls about 16 years ago (Grocko bronze replacements) and we reinstalled all 3 of those check-valves.
I tried to open the top-mounted inspection cap on each of them...but could not get them to budge.....maybe we should have left them off?
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Old 16-06-2021, 09:35   #8
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Re: Marine Sink Check Valves

Great posts..........just to add my powerboat and sailboat do not have a check valve in the sink drains. Primary reason is check valves should only be used in clean service to mitigate the risk of plugging, they add pressure drop which restricts flow, are prone to fail open or close. If you feel you need one in this service, suggest they are located above the water line as you indicated to mitigate risk of sea life plugging it and accessible for ease of maintenance or replacement.
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Old 16-06-2021, 09:36   #9
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Re: Marine Sink Check Valves

If you choose to re-install a check valve they require maintenance just like any other mechanical valve. I chose to when re-doing all our through hulls. Our originals never saw service and we’re broken open (bronze groco type) when we hauled out to replace them (pontoon lift) I forgot to close a through hull and the pressure from the pontoons forced water back up the head sink and nicely coated the entire head floor to ceiling. Prior to replacing we did get gurgling and occasionally some water back up in the sink when trying to wash your hands underway (pipes full plus back pressure= slow draining & backup) A little grease on the inspection cap threads and remove annually for cleaning and service is pretty easy.
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Old 16-06-2021, 09:39   #10
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Re: Marine Sink Check Valves

I have a Tayana 47 and can assure you the check valve is needed on the galley sink. You will get an excessive amount of water back up and sloshing around the sinks. Same for the front head sink if your configuration has one. I can assure you this is from the voice of bitter experience.

Our galley sink thru hull was under the stove and a pig to get to and I could not get a replacement valve to fit back in there. I moved the one way valve back up to directly under the sink and it has worked without a problem for the last ten years.

The first trip out without a one-way valve in the front sink resulted in about 100 gallons of water before we noticed and shut the thru-hull off. I had enough room to place the valve on the thru-hull valve but it is prone to gumming up and would have been better onto the bottom of the sink.

The rear head sink has not had a problem but I put a one way valve back on just in case.

Hope this helps.

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Old 16-06-2021, 09:53   #11
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Re: Marine Sink Check Valves

We have a 35 year old plastic gate valve right below the head sink that I will sometimes close when I know we will be beating into heavy weather as sometimes a bit of water does flow back.onto the counter if left open Works like a charm for the last 20 years
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Old 16-06-2021, 09:56   #12
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Re: Marine Sink Check Valves

Both of my sinks have a simple flapper mechanism installed halfway up on the hose (well above the waterline). They came with the boat in 96. They are not proper check valves, but they do limit splash from waves as I had a flapper fail (i.e., broke off). I would not trust them against slow flooding.

I suspect the question of usefulness depends on the boat. Mine is a 30-foot conoe body with a long keel (cut-away forefoot) and skeg-hung rudder and a displacement less than 9000 pounds.
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Old 16-06-2021, 10:03   #13
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Re: Marine Sink Check Valves

The sink in question happens to be the for the aft head which adjoins the master/ aft stateroom and as such is in very frequent use, especially offshore. Frequently opening and closing the sea cock is not really viable. It is behind the head it a closet under needed storage. You can get there but it is inconvenient.

The orientation of the check valve was fore and aft after a 90 degree elbow so the original install was viable but marine growth would have quickly seize up the swing. The way mine was stuck in place, it acted like an orifice, restricting flow both ways. I always wondered why that sink drained slowly (but not unacceptably slow).

I have renewed many of the thru hulls/ seacocks but not this one. Other than being seized, the thru hull/ seacock was not the issue, the down stream plumbing was the weak link. This is the only one where I would say the install was faulty from the original build.

Sounds like I'll be keeping the forward head check valve. Thanks Gemini!
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Old 16-06-2021, 10:20   #14
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Re: Marine Sink Check Valves

I have rarely heard of check valves in sinks, but I guess some are used. Seems to me they are going to freeze or clog/leak with hair etc. If bronze I guess they are installed horizontal..? Who builds a boat with sinks below waterline? It's a band aid for an issue discovered after launch I guess.
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Old 16-06-2021, 11:09   #15
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Re: Marine Sink Check Valves

Various sizes of PVC check valves are dirt cheep at local hardware stores but don't spread it around or they will all of a sudden become expensive if they find out you want to put them in your boat.

The same with airplane parts. The same little tail light bulb that you would install in a small airplane is $45 it to be installed for a nav lite. Of course they are all made on the same assembly line but the airplane ones are pulled off and go into a box with the FAA's TSO (Technical Standards Order) approval printed one the box.
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