Anti-syphon loops

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Graham_Wright

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www.mastaclimba.com
For a sea toilet installation, we are urged to instal above-water loops for toilet waste outlet and flushing water inlet, the latter after the pump.

We are also urged to use anti-syphon valves in these loops.

Accepting that, should they be valved (nrv) or vented to deck?

All opinions welcomed.
 
chrisbitz said:
it's an all in one self contained part.


Easy to fit, just make sure the valve is above the waterline at any angle
Click to expand...

I have heard the valves can become blocked (and not something I would like to unblock!)

They (all) seem to be ridiculously expensive. Compare with an anti-syphon valve for domestic installations which are much more complex and considerably cheaper.
 
Graham_Wright said:
I have heard the valves can become blocked (and not something I would like to unblock!)

They (all) seem to be ridiculously expensive. Compare with an anti-syphon valve for domestic installations which are much more complex and considerably cheaper.
Click to expand...

Not sure why you should be worried about them blocking as they are only there to let the air in to prevent sewage from syphoning back. If you are pumping the right amount then the pipe only contains water on the up loop and is empty on the down, at least as far as the waterline. The valve in the water inlet is not necessary on most installations where the loo is above the waterline and the latest pumps stop syphoning anyway, so valve is belt and braces.
 
Graham_Wright said:
For a sea toilet installation, we are urged to instal above-water loops for toilet waste outlet and flushing water inlet, the latter after the pump.

We are also urged to use anti-syphon valves in these loops.

Accepting that, should they be valved (nrv) or vented to deck?

All opinions welcomed.
Click to expand...

Valved!
You dont really want to be wasting flushing water.... It's best used to flush the loo and you definitely don't want to discharge any toilet effluent on to the deck

( Engine cooling water antisyphon loops OTOH can usefully be discharged somewhere visible, like an outboard engine telltale, so that you can see that all is well. )
 
VicS said:
Valved!
You dont really want to be wasting flushing water....
Click to expand...
The sea is quite big!

It's best used to flush the loo and you definitely don't want to discharge any toilet effluent on to the deck
Click to expand...

A non-valved loop could be connected through the hull below the gunnels. Come to think of it, I could connect into the black water ventilation hose.

Thanks for the brain storm!
 
Graham_Wright said:
For a sea toilet installation, we are urged to instal above-water loops for toilet waste outlet and flushing water inlet, the latter after the pump.

We are also urged to use anti-syphon valves in these loops.

Accepting that, should they be valved (nrv) or vented to deck?

All opinions welcomed.
Click to expand...

Look, I'm no expert so please correct me if I am wrong.

The inlet for the flushing water must be below the waterline so that sea water flows through the ball valve (attached to the skin fitting) to the toilet. If the toilet is below the waterline the toilet would overflow and eventually sink the boat. So they loop the sea water inlet tube up above the waterline (up near the deck) and then back down to the toilet. You'd reckon that would solve the problem but it doesn't as the water can start siphoning, overflow the toilet bowl and eventually sink the boat. So that is why an anti-siphon valve is required to stop siphoning.
I have never heard of an anti-siphon loop on the waste outlet pipe but I will be pumping into a holding tank..
 
Last edited:
coopec said:
Look, I'm no expert so please correct me if I am wrong.

The inlet for the flushing water must be below the waterline so that sea water flows through the ball valve (attached to the skin fitting) to the toilet. If the toilet is below the waterline the toilet would overflow and eventually sink the boat. So they loop the sea water inlet tube up above the waterline (up near the deck) and then back down to the toilet. You'd reckon that would solve the problem but it doesn't as the water can start siphoning, overflow the toilet bowl and eventually sink the boat. So that is why an anti-siphon valve is required to stop siphoning.
I have never heard of an anti-siphon loop on the waste outlet pipe.
Click to expand...

I think the same problem arises.

I understand the reasons - I'm just seeking the tight-wad answer!
 
Graham_Wright said:
I have heard the valves can become blocked (and not something I would like to unblock!)

They (all) seem to be ridiculously expensive. Compare with an anti-syphon valve for domestic installations which are much more complex and considerably cheaper.
Click to expand...


Yes, the valves can become blocked so they require regular maintenance.

Three months ago I bought two 12mm plastic anti-siphon loops for about $A10.50 each of eBay. I am trying to find them again at that price but haven't found them yet. There's nothing to them - they'd fit into your lunchbox.
 
I accept that it is possible for a siphon to be established, but the (old) boats I've sailed on all had loops above the waterline but no vents and I've never seen a siphon actually occur. I guess it's rather like using gas on a boat, the best prevention is to close the seacocks when they are not in use. Having said that, when fully crewed I don't bother to close them as there is more frequent use and crew traffic below who would notice the flow of water should it happen. Unfortunately, the previous owner installed gate valves on the hoses, so it is a bit of a pain to open and close them but at least it keeps them exercised. If they have ball valves or Blakes style lever operated valves, then it is definitely the best option to close them.

Rob.
 
Graham_Wright said:
I understand the reasons - I'm just seeking the tight-wad answer!
Click to expand...

The tightwad answer is yes on the inlet but no on the outlet pipes (maybe). I have a Lavac set up like this. I think the likelihood of getting a full column of water in the outlet pipe is zero. The inlet pipe, being much smaller diameter, cannot carry enough water to fill the larger diameter of the outlet pipe. Without a full column of water in the outlet it cannot syphon.
 
The difference between the two is that the outlet hose will always have the joker valve to prevent siphoning. If the joker valve has failed the bowl will be filling with water after every flush, which should give adequate warning. With the inlet it is theoretically possible for water to flow straight to the bowl with minimal hindrance. Having said that, Sadler plumbed my boat with a loop for the outlet but not the inlet. The toilet is well above the water line though.
 
The cheapest I can find on eBay now is $A40 which is a rip-off. As I said I bought mine for $A10.50 each a few month ago.
 
alahol2 said:
The tightwad answer is yes on the inlet but no on the outlet pipes (maybe). I have a Lavac set up like this. I think the likelihood of getting a full column of water in the outlet pipe is zero. The inlet pipe, being much smaller diameter, cannot carry enough water to fill the larger diameter of the outlet pipe. Without a full column of water in the outlet it cannot syphon.
Click to expand...

The Lavac is rather different, at least assuming the OP is talking about a Jabsco or similar.

The Lavac has a small air bleed hole in the inlet pipe which releases the vacuum and breaks the syphon so no valve in the top of the inlet loop.

Its pump is in the outlet and no vent valve is need in the discharge loop after the pump because valves in the pump will normally prevent back syphoning and the flushing process introduces sufficient air to prevent it syphoning anyway.
 
VicS said:
The Lavac is rather different, at least assuming the OP is talking about a Jabsco or similar.

The Lavac has a small air bleed hole in the inlet pipe which releases the vacuum and breaks the syphon so no valve in the top of the inlet loop.

Its pump is in the outlet and no vent valve is need in the discharge loop after the pump because valves in the pump will normally prevent back syphoning and the flushing process introduces sufficient air to prevent it syphoning anyway.
Click to expand...

Agree entirely but I still reckon that you couldn't pump enough water through the small inlet pipe to fill the larger outlet pipe. Without the outlet pipe being full it will not syphon. Whatever type of loo you've got.
 
Graham_Wright said:
For a sea toilet installation, we are urged to instal above-water loops for toilet waste outlet and flushing water inlet, the latter after the pump.

We are also urged to use anti-syphon valves in these loops.
Click to expand...

I am struggling to see why the inlet loop must be after the pump. Sure, the pump will start faster that way, but I think putting the loop before the pump would allow you to use a small air hole (no special 'valve' required) at the top of the loop, as per Lavac described by Vic.

VicS said:
The Lavac has a small air bleed hole in the inlet pipe which releases the vacuum and breaks the syphon so no valve in the top of the inlet loop
Click to expand...
 
LittleSister said:
I am struggling to see why the inlet loop must be after the pump. Sure, the pump will start faster that way, but I think putting the loop before the pump would allow you to use a small air hole (no special 'valve' required) at the top of the loop, as per Lavac described by Vic.
Click to expand...

And then the pump will just suck in air instead of water.

I dare say it would work with a powerful diaphragm pump that could create enough suction to lift water up the loop despite the inflow of air. But the Jabsco flush pump is not especially powerful, so any handicap (like introducing air on the suction side) is to be avoided.

Pete
 
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