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Old 12-08-2019, 15:31   #1
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Electric toilet water intake sucked dry by venturi effect when sailing

I have installed an electric toilet on my Jeanneau 40 . It works great when at dock, but I noticed that when sailing fast, when I flush it, there is no water flowing into the bowl.


When I got back to dock, I looked at the hose coming from the through hull valve and it was empty past the waterline. When I flushed the toilet, I could see the water coming up the hose and then into the toilet as it should. I presume that the venturi effect is sucking the water out of the tube while sailing fast.


Is there any solution to this? Perhaps some kind of one-way valve that I could put in the system or a special something that could be mounted over the outside of the through hull to stop the effect?
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Old 12-08-2019, 16:21   #2
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Re: Electric toilet water intake sucked dry by venturi effect when sailing

Try closing the intake seacock. If that's inconvenient, use a cup from the sink to provide flush water.

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Old 12-08-2019, 16:37   #3
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Re: Electric toilet water intake sucked dry by venturi effect when sailing

I thought it was best practice to close these seacocks before getting under way anyway. Itís all about minimising risk.
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Old 12-08-2019, 18:42   #4
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Re: Electric toilet water intake sucked dry by venturi effect when sailing

What kind of intake strainer do you have? Itís not a scoop facing backwards is it?
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Old 13-08-2019, 03:12   #5
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Re: Electric toilet water intake sucked dry by venturi effect when sailing

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What kind of intake strainer do you have? Itís not a scoop facing backwards is it?

There is no "scoop". It is just a through hull valve with a regular opening.
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Old 13-08-2019, 03:47   #6
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Electric toilet water intake sucked dry by venturi effect when sailing

There should be a siphon break in most flush water supply hoses. It depends on the location of head relative to waterline and the head design. Check your installation manual to be double sure you donít need a siphon break between the pump and bowl. If there is a siphon break then it isnít working. A working siphon break should prevent the bowl getting sucked dry.

Closing the intake seacock when not using the head is a best practice.
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Old 13-08-2019, 08:30   #7
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Re: Electric toilet water intake sucked dry by venturi effect when sailing

You can purchase a bronze scoop intake for short money from Westmarine and afix it to to hull around the present thru hull fitting. Face it forward so it draws water into the truhull when underway. We use a couple of these, only about $20 from your local chandlery.

Problem solved.
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Old 13-08-2019, 08:48   #8
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Re: Electric toilet water intake sucked dry by venturi effect when sailing

My Raritan does the same thing, but it will intake water after energising the pump to flush. I don't worry about it.
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Old 13-08-2019, 11:11   #9
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Re: Electric toilet water intake sucked dry by venturi effect when sailing

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You can purchase a bronze scoop intake for short money from Westmarine and afix it to to hull around the present thru hull fitting. Face it forward so it draws water into the truhull when underway. We use a couple of these, only about $20 from your local chandlery.

Problem solved.
I think this is not a good idea. Pushing water into a toilet bowl while underway is a recipe for flooding. Better that it gets sucked dry than have it overflow.

Close the seacock then figure out why a vacuum can be created where there should be none. Use a vacuum break (anti-siphon loop) as appropriate.
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Old 13-08-2019, 14:33   #10
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Re: Electric toilet water intake sucked dry by venturi effect when sailing

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...a siphon break...



Quote:
Originally Posted by transmitterdan View Post
...anti-siphon loop...




I'm not sure what these terms mean specifically. The install instructions for the toilet said that the intake should loop up above the waterline - which I did. Is this supposed to be a one-way valve or something?
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Old 13-08-2019, 17:30   #11
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Re: Electric toilet water intake sucked dry by venturi effect when sailing

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I'm not sure what these terms mean specifically. The install instructions for the toilet said that the intake should loop up above the waterline - which I did. Is this supposed to be a one-way valve or something?
https://www.defender.com/category.js...4&path=-1%7C51

After thinking about this some more i donít think the water is being sucked out via the incoming water supply line. It is most likely sucked out via the overboard waste discharge line. If you pump directly overboard without a holding tank then you definitely need an anti-siphon device in the discharge line well above the heeled water line.
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Old 13-08-2019, 17:36   #12
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Re: Electric toilet water intake sucked dry by venturi effect when sailing

Our heads have a pump that can pull from fresh water or sea water based on a couple of valves. Do you have the same arrangement? If you do and the pump is working ok, it should suck harder than an Venturi effect.
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Old 13-08-2019, 19:17   #13
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Re: Electric toilet water intake sucked dry by venturi effect when sailing

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Originally Posted by transmitterdan View Post
https://www.defender.com/category.js...4&path=-1%7C51

After thinking about this some more i donít think the water is being sucked out via the incoming water supply line. It is most likely sucked out via the overboard waste discharge line. If you pump directly overboard without a holding tank then you definitely need an anti-siphon device in the discharge line well above the heeled water line.
I'm sorry for getting your issue confused with another one. You reported that the supply water line is getting emptied when sailing not the discharge line.

So there is another possibility. If the supply through hull is close to the water line then when the boat is heeled when sailing the line will drain. When the boat stands back up straight it will trap air. Is this scenario possible? If so, then there isn't really anything you need to do about it.

But you really should review the installation instructions for the new toilet and be sure you followed all the instructions.
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Old 14-08-2019, 13:12   #14
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Re: Electric toilet water intake sucked dry by venturi effect when sailing

Bernoulli effect. Where velocity of a fluid increases, lateral wall pressure decreases. If one can prevent the velocity from increasing then the lateral wall pressure will increase.
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Old 14-08-2019, 16:41   #15
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Re: Electric toilet water intake sucked dry by venturi effect when sailing

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Bernoulli effect. Where velocity of a fluid increases, lateral wall pressure decreases. If one can prevent the velocity from increasing then the lateral wall pressure will increase.
Sail slow.
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