Jabsco inlet anti-syphon - why?

[LittleSister]

Putting an anti-siphon valve before a suction pump (whether engine or toilet) is pointless, because the pump will just suck in air through the valve instead of sucking in water.

That's not strictly true: Whether the suction pump will suck in only air will depend on the size of the air inlet. (Or more strictly, the relative size and height of the air and water inlets.)

Lavac sea toilets always have an air vent in the inlet between the seacock and the toilet/suction pump, but it is only tiny, so it doesn't let much air in. It is not enough to significantly reduce the amount of water the suction pump can pull through, but it is enough, once pumping is stopped to break the potential syphon and to release the vacuum which would otherwise prevent the lid from being lifted again. (The pump is on the 'downstream' side of the toilet, and the sealing toilet seat lid allows the pump to simultaneously suck water in and force waste out.)

 

[prv]

That's not strictly true: Whether the suction pump will suck in only air will depend on the size of the air inlet. (Or more strictly, the relative size and height of the air and water inlets.)

True. The main culprit is in engine water systems where the impeller is whizzing round trying to prime, not yet making a huge amount of suction, and just being fed uselessly with air from the wrongly-placed valve. A dirty great toilet pump operated with gusto is going to overcome a dinky little air inlet, but it's still not ideal.

Pete

 

[Robin]

Mostly because of the joker valve in the toilet, I imagine. But the makers say not to rely on that.

Pete

We have a non-return ( Check) valve in ours to prevent any backflow to the bowl from the residual outlet pipe contents . This is in addition to the joker valve and twist 'n lock and as recommended by our local loo guru.

 

[Ric]

We have a non-return ( Check) valve in ours to prevent any backflow to the bowl from the residual outlet pipe contents . This is in addition to the joker valve and twist 'n lock and as recommended by our local loo guru.

Interesting. I considered doing this, but was advised (on here) that the joker valve would benefit from a head above. Also, I was slightly concerned that the restriction might be a cause of blockages. Have you ever had one?

 

[webcraft]

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I've had no anti-syphon loops for twelve years now and never had any back-syphoning. Last six years have had a twist-and-lock system. Outlet pipe is one inch long!

Seacocks are left open in calm weather but usually closed on passage.

Advantage is easy flushing and absolutely no smell.

- W

 

[Nicholas123]

The twist & lock system looks sufficient to me & I think they are just scare mongering or trying to sell you additional equipment.

 

[Robin]

Interesting. I considered doing this, but was advised (on here) that the joker valve would benefit from a head above. Also, I was slightly concerned that the restriction might be a cause of blockages. Have you ever had one?

No, not had bockages. We first had a check valve fitted by our guru when we lived on a 47ft motor yacht ( 2loos oppositeends of boat from one huge holding tank) and had problems with the then electric loos getting a drain back into the bowl. The check valve addition is quite common here and we added them to bilge pump outlets too. On our current (sail) boat the holding tank is a tall vertical one and the pie to it enters at the top, hence there is say 6ft of pipe potentially full of liquid that cold drain back down. The usual solution of giving many more pumps to fully empty the pipe would be likely to put more flush water into the holding tank, potentially filling it sooner than we might like. I should say we had no real problem with backflow, but were installing a brand new toilet to replace the original and standard Jabsco one which the previous owner had modified from manual to electric operation and which leaked. A new electric pump or rebuild kit was more expensive than buying a complete new manual twist 'n lock Jabsco which is the option we chose together with the check valve recommended by our guru who is renowned here ( Florida) in all matters loo, right up there with the great Peggy Hall He was/is 'anal' about smooth and clear pipe runs with no sharp bends or unnecessary restrictions and insists always on the very best quality 'Y' valves, check valves etc.( he replaced the existing Y valve for that reason with a better design, more expensive version)

 

[johnalison]

The main reason why syphoning doesn't occur in loo outlets is that most people continue pumping until there is air in the pipe. I regard it as good practice to do this as a routine, though I to have a twist-and-lock valve.