Toilet anti siphon

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melvynpatrick

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I have two Blake’s toilets on board. Not the lavac, the big old bronze ones. They both work beautifully. The forward one is below the waterline. The inlet water is through a Blake’s seacock and then to a tap (sic) on the back of the toilet. You keep the tap closed or the inlet water fills up the toilet and then the rest of the boat. For belts and braces you can close the seacock too. Because guests often forget to turn off the tap I decided to fit a siphon break from force 4. This works a treat if people forget the tap. However when flushing the toilet it sucks air too much and you have to put a finger over the valve so you can pump water in easier. This is a bit of a nuisance. Is this phenomenon just inherent in anti siphon loops or have I bought the wrong one. Thanks.
 
melvynpatrick said:
I have two Blake’s toilets on board. Not the lavac, the big old bronze ones. They both work beautifully. The forward one is below the waterline. The inlet water is through a Blake’s seacock and then to a tap (sic) on the back of the toilet. You keep the tap closed or the inlet water fills up the toilet and then the rest of the boat. For belts and braces you can close the seacock too. Because guests often forget to turn off the tap I decided to fit a siphon break from force 4. This works a treat if people forget the tap. However when flushing the toilet it sucks air too much and you have to put a finger over the valve so you can pump water in easier. This is a bit of a nuisance. Is this phenomenon just inherent in anti siphon loops or have I bought the wrong one. Thanks.
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Doesn't sound right. I have anti syphon loops on both my electric toilets and no such issue. Faulty valve in the anti syphon or maybe needs to be closed down a bit tighter to seat it properly.
 
Irish Rover said:
Doesn't sound right. I have anti syphon loops on both my electric toilets and no such issue. Faulty valve in the anti syphon or maybe needs to be closed down a bit tighter to
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Aah. Maybe that’s it. There is a plastic nut shaped thing on the valve. Didn’t realise it should/could be tightened.
 
Don't tighten it too much or you might distort the little valve inside. That top of that valve should seat into the plastic nut with the top of the valve flush with the top of the nut, with its circular shape visible on the top of the nut and not distorted. You could unscrew the nut (careful not to lose the valve) and check that it's undamaged and not distorted.
 
Dellquay13 said:
On non Blakes toilets such as Jabsco, the AS valve goes after the pump, before the bowl. The pump then gets full suction from the seacock but the siphon action is broken before the bowl.
Can it be fitted in this order on your toilet?
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I don’t think I would be able to do this on a blakes
 
PeterBoater said:
Don't tighten it too much or you might distort the little valve inside. That top of that valve should seat into the plastic nut with the top of the valve flush with the top of the nut, with its circular shape visible on the top of the nut and not distorted. You could unscrew the nut (careful not to lose the valve) and check that it's undamaged and not distorted.
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I’ll have another look. Although thinking again. And looking at others on the internet. I bought a trudesign vented loop. From what you’re saying I might have bought the wrong thing and it’s not an anti siphon valve at all! Sounds like something stupid I would do
 
melvynpatrick said:
I’ll get one of those. Cheers
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The one you bought seems to be intended for the purpose as well - this is what they say on their website
Vented loops are used predominantly in toilet to overboard applications, toilet inlet applications and holding tank to overboard applications. They can also be used in genset or small engine inlet cooling water systems. The simple one way breather valve at the top of the vented loop allows air to enter the line when not in use, thereby preventing siphoning - and yet seals when water or waste passes through the loop. The duckbill one way valve is designed to seal even when particles are present in the fluid.
It's possible therefore you have another issue and a different loop will not solve it.
 
melvynpatrick said:
I’ll get one of those. Cheers
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Before you possibly spend money unnecessarily, the one you have looks the same in principle as the other one, so perhaps you might look elsewhere for the source of the problem, as just buying another make of anti-siphon loop might not cure the problem (assuming that the loop you have is working correctly, as in my earlier post).
 
Not knowing exactly what you have but thinking from first principles. If you have a siphon break between the seacock and pump, air will be drawn in on use because the water pressure is lower than atmospheric. If the loop is between pump and toilet the water pressure will be greater than atmospheric, the small valve will close and air will not be admitted.

You have a situation similar to that with a Lavac. There is a siphon break air valve on the suction side but its size is kept low to avoid the situation you have. You need to partially close the air inlet so that air intake is present but not so much that it causes suction problems. Reduce the size of the air vent but do not close it off.
 
Thank you for that. That’s a good idea. I did think maybe the hole was too big. I had a lavac on my last boat and the hole in the pipe was tiny
 
Lavacs come with various sized buttons to insert in the flush line as a siphon/ vacuum break, mine was fitted with a anti syphon like your image, and the toilet did not draw in any flush water. with some experimenting I plugged up the vent and then made a small hole with a sail needle.. works fine now..
 
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