Converting Jabsco Electric conversion to FW flush - NRVv Reqd ?

[superheat6k]

My seatoilets have the Jabsco electric conversion units. The aft loo is plagued with debris entering the inlet rendering the flush really weak.

So to convert to fresh water flush I intend to simply install a 12v solenoid adjacent to the cold tap feed on the nearby sink, then this will route directly to the flush connection on the back of the loo. To disable the inlet flush pump I am simply removing the upper impeller, and blocking off the bypass impeller wetting tube from the lower pump.

Do I need to fit a Non-return valve after (or before) the solenoid to prevent any chance of contamination being drawn back in to the domestic water system ?

Can't see how a back-flow could happen as the fresh water is operating at about 3 bar, and the flush end will be open to atmosphere.

 

[prv]

Can't see how a back-flow could happen as the fresh water is operating at about 3 bar, and the flush end will be open to atmosphere.

It's only at 3 bar as long as the FW pump is running...

I'm not sure I'd fancy it even with a non-return valve, to be honest. The pukka approach is with a small header tank that the water falls into via an air-gap, so that there's no way anything can get from the loo into the supply - essentially the same as a shoreside toilet cistern. But it's you that drinks the water, not me...

Pete

 

[nigelmercier]

Don't even think about it without a header tank. Have you not noticed how these units recycle the outflow into the input?

 

[prv]

Don't even think about it without a header tank. Have you not noticed how these units recycle the outflow into the input?

To be fair, he's proposing to bypass the built-in heads pump entirely, so that issue doesn't arise. But he is planning to connect his freshwater system directly to his toilet bowl...

Pete

 

[superheat6k]

My fresh water system is continually pressurised when I am onboard and the boat is 'switched on'. I suppose I should ask how boats using fresh water flush as standard direct from the cold water system do this ? I know they don't have a cistern arrangement.

Could bacteria grow back along the pipe when the boat is idle.

The aft heads is at least 6m from the pump.

 

[Alpha22]

Could bacteria grow back along the pipe when the boat is idle.

Yes!!!

 

[David2452]

None of the toilets provided with solenoids taking domestic pressure cover it in their documentation, usually just showing direct connection. However if you connected one to a domestic (household) system you would be in breach of cat 5 fluid contamination protection regs. No regs for a boat but they are there for a reason, an NRV wouldn't help as the solenoid is already doing that when not operating. Retention of the pump fed from some kind of small cistern with an air break is what is needed for surity.

 

[superheat6k]

I now learn that whereas the majority of Mobos simply rely upon the Solenoid valve to act as an NRVv, Jabsco specify a solenoid with built in siphon breaker to allow the water to drain away from the valve into the loo bowl after a flush, providing an air break.

Lee San recommend a domestic double check valve, but they also offer a vented loop / siphon breaker, which with a separate RS supplied 12 v solenoid just upstream works out massively cheaper than the Jabsco item and achieves the same aim.

I will have a downhill run from the vented loop into the loo, and for good measure I will also fit a double check valve before the solenoid, especially as the RS supplied NRVv I have bought seems to act as an NRVv in the wrong direction when I blow into it.

It would seem most Moboers are blissfully unaware of the potential danger of their sanitary systems, especially those without NRVvs just relying on the solenoid valve acting as NRVv, and with liquid in permanent flooded contact either side of the seat I can easily see how bacteria could breech the valve.