Fresh water toilet flush systems

[superheat6k]

I am thinking about converting to fresh water flush. What are the standard means on production boats with fresh water flush loos to ensure there is no possibility of contaminants travelling back into the fresh water system from the loo ?

I assume such loos are not using cisterns.

 

[sunquest]

The fresh water for my Jabsco electric toilets is connected to the water supply via a T piece and a non return valve.

 

[jfm]

The toilet manufacturers generally advise that you use their official valve and not a generic solenoid valve. I'm not sure I can see any special features consistently on the official valves but I've always used them and never had a problem. Maybe they have a NR valve integrated into the valve. The jabsco one has an antisyphon device and the Tecma one doesn't, so it's hard to conclude anything from that. You are right to think about it though

 

[superheat6k]

The toilet manufacturers generally advise that you use their official valve and not a generic solenoid valve. I'm not sure I can see any special features consistently on the official valves but I've always used them and never had a problem. Maybe they have a NR valve integrated into the valve. The jabsco one has an antisyphon device and the Tecma one doesn't, so it's hard to conclude anything from that. You are right to think about it though

So it is fair to say that most if not all fresh water flush systems on Mobos are fed direct from the pressurised fresh water system, via some form of NRVv, but no air break device, i.e. a cistern.

I asked a similar question on the PBO forum and one would have thought Hades himself had suggested this !

One respondent even quoted the specific regulation for this for a shoreside loo. Not sure where this falls under the RCD !

So a good blast of bleach into the flush ring before I leave the boat and a 15 - 20 second flush through when I next return.

 

[MapisM]

So it is fair to say that most if not all fresh water flush systems on Mobos are fed direct from the pressurised fresh water system, via some form of NRVv, but no air break device, i.e. a cistern.

Yep, afaik it's fair to say that.
Otoh, the chap which made the conversion on my boat placed the solenoid valves higher that the bowls, fwiw.
Therefore, the last part of the hose - I'd say a couple of feet or so - remains empty at all time but when flushing.
Not sure you can call it a real air break device, and TBH I never thought about the point you're raising before (which is a good one anyway).
So, I'm not even sure if this is the reason why he placed the solenoids where he did, and it might well be just a coincidence...
...though coming to think of it, it surely doesn't hurt to do the same, space permitting.

 

[sunquest]

So it is fair to say that most if not all fresh water flush systems on Mobos are fed direct from the pressurised fresh water system, via some form of NRVv, but no air break device, i.e. a cistern.


So a good blast of bleach into the flush ring before I leave the boat and a 15 - 20 second flush through when I next return.

Not sure bleach is a good idea! damage to rubber components comes to mind

 

[jfm]

So it is fair to say that most if not all fresh water flush systems on Mobos are fed direct from the pressurised fresh water system, via some form of NRVv, but no air break device, i.e. a cistern.

Yup, it's fair to say that. Millions of units installed, including a dozen++ that I've had myself, with no problems

 

[superheat6k]

I have discovered that Jabsco offer their freshwater units with a siphon breaker built in to the solenoid valve, making it an uber-expensive solenoid valve. However, if I install a simple siphon breaking vented loop downstream of the solenoid valve at the high point of the adjacent cupboard this will allow the line down to the head bowl to drain after each flush, thus providing the required air break.

This would do the same job as the Jabsco device but at considerably less cost, and likely easier to install.

Thanks for the advice.

 

[MapisM]

Mmm... As I said, I'm not pretending that the arrangement I've got on my boat, with the last 2 feet of hose going straight downhill from the solenoid valve to the bowl, could be good enough to pass the sterilization requirements of a surgery room , far from that.
But frankly, I don't think a siphon would add a lot of protection compared to just an empty hose, in this case.
If your concern is contamination through air, that's still quite possible also with a vented siphon.
Besides, I'm wondering if the bit of water stagnating inside the siphon between each flush couldn't be more exposed to contamination, which could potentially backfire while flushing, if you see what I mean...