Fresh water flushing 2

[PCUK]

After massive thread drift on the PBO forum and a lot of talking cr*p (literally) I'll try again here.
All my previous systems have been sea water flush but this time I want to use fresh water from the tank. The toilet is a Jabsco Liteflush and the instructions say not to flush via a pressurised water system which is understandable. If I connect the flush between the tank and the pump via a non return valve so it is before the pressurised side and the toilet pump draws the water from the tank in the same way as it would from the sea, is that more or less the normal method for fresh water flushing?
Answers preferred from those actually using such systems to avoid more thread drift please.

 

[MapisM]

Can't speak for the Jabsco Liteflush, but Tecma for instance does work with the pressurised fresh water circuit.
Flushing is handled by an electric valve opening and closing the fresh water inlet, and the toilet pump only deals with the discharge.
If Jabsco restricts from using pressurised water, at a guess it's because it doesn't have any valves, and there's a pump sucking sea water (or fresh, as connected).
If so, your idea should work, but aside from possible contamination problems, I'd be concerned that when the tank level is low, the toilet pump might be unable to suck the water.
Though that depends on the tank and toilet position, of course.

 

[jfm]

No that is definitely not normal, and feels a bit p-poor to me. Normal method is to flush from the boat's pressurised fresh water, with a solenoid valve controlling the flush on/off. I don't see why you say "which is understandable"

Exactly as Mapism says

This is how Tecma do the flushing. Excuse me for calling a spade a spade but jabsco WCs are substantially inferior to Tecma. Tecma seem to have designed a WC that works properly without worrying too much about cost. Porcelain bowl and well designed pump with huge motor. Makes jabsco look like a bit of a toy

 

[PCUK]

Thanks JFM, but the Jabsco instructions specifically say not to connect to pressurised water. My assumption is that there is no facility to positively shut off the flow from the domestic pump which may therefore continue to run. An electric valve in the system a la Tecma should work equally well with the Jabsco. Good point about the low water pumping Mapism. However, in this instance the toilet is installed not far above the fresh water tank level and according to the spec' sheet there will be more than enough lift in the flush pump to avoid problems with a low water level.

 

[jrudge]

My Jabsco on Targa 40 is fresh water flush. Just feeds from the boats water supply. If there was no pressure behind the water .... it would never flush!

Is the toilet you are buying designed for freshwater flush? I would not think that connecting the toilet to the tank regardless of a non return valve is the best of ideas.

If an existing toilet then either purchase a proper freshwater kit or replace it. They are not dear and if a few years old it prob needs new seals etc. anyway.

 

[rustybarge]

Is the toilet you are buying designed for freshwater flush? I would not think that connecting the toilet to the tank regardless of a non return valve is the best of ideas.

Just wondering, with a manual or electric jabsco, whether nasty bacteria and virus' from the poo pipe could migrate past the plunger or pump and into the fresh water tank.....

On my manual Jabsco there would be nothing to stop that happening...:ambivalence:

On a domestic loo the cistern is not connected to the waste pipe, and the water feed to the cistern is with a ballcock and above the level of the water; so there can be no backwards flowing contamination.

PS: A small fresh water 'day tank' to supply the loo would isolate it from the fresh water tank.

 

[PCUK]

The toilet is a new electric Lite Flush and all the instructions say is to not connect it to a pressurised water system, but not why. So I'm not going to! The toilet has totally separate flush and pump-out pumps so no cross contamination is possible. If I draw out of the tank before the pressure pump it is no different to drawing straight out of the sea. The non return valves are there strictly to prevent either pump trying to draw through the other and possibly causing air locks in the system not to prevent water contamination. All I am trying to ascertain is whether there is any technical (rather than hygiene) reason not to do it this way. I think the best thing I can do is make the installation and report back on how it works. I should have mentioned that the main reason for doing it this way is to simplify the pipe-work as the toilet is awkwardly placed for running additional pipe-work and conveniently locating an accessible sea-cock.

 

[rustybarge]

The toilet is a new electric Lite Flush and all the instructions say is to not connect it to a pressurised water system, but not why. So I'm not going to! The toilet has totally separate flush and pump-out pumps so no cross contamination is possible. If I draw out of the tank before the pressure pump it is no different to drawing straight out of the sea. The non return valves are there strictly to prevent either pump trying to draw through the other and possibly causing air locks in the system not to prevent water contamination. All I am trying to ascertain is whether there is any technical (rather than hygiene) reason not to do it this way. I think the best thing I can do is make the installation and report back on how it works. I should have mentioned that the main reason for doing it this way is to simplify the pipe-work as the toilet is awkwardly placed for running additional pipe-work and conveniently locating an accessible sea-cock.

The fresh water pump on the Jabsco probably probably has a flow rate several times the domestic flow on your boats pressurised water system.....if you connect it up to the domestic system the Jabsco will wreck your domestic water pump seals and rubber valves.:ambivalence:

 

[jfm]

Thanks JFM, but the Jabsco instructions specifically say not to connect to pressurised water.

Yup, but I was just answering your question ("is it normal?")

You have the instructions but alas they relate to a Jabsco loo which is a sort of 4 out of 10 product to begin with. You gotta decide whether the follow the instructions or not. If you choose not, then you will need to get a solenoid valve and you'll be taking a chance as to whether the pressure in your domestic water matches the spray nozzle pattern of the WC so as to get a nice cleaning action. Maybe needs a bit of trial and error. Furthermore, you'll need to use Jabsco's timer circuit that would have controlled the flush pump to control the solenoid valve - that might work ok but I'm not sure

Easiest thing is therefore perhaps to fit the thing as the instructions say and hope it works ok. (Or take back to shop and swap for a Tecma )

 

[PCUK]

I'm not going through the domestic pump. That's the whole idea. The take-off will be before the pump and therefore not on the pressure side so the toilet will do all its own pumping and won't know it is pulling out of the tank rather than the sea.

 

[rustybarge]

I'm not going through the domestic pump. That's the whole idea. The take-off will be before the pump and therefore not on the pressure side so the toilet will do all its own pumping and won't know it is pulling out of the tank rather than the sea.

Just a thought: If you already have a pressurized water feed to your heads, why not fit a small plastic accumulator tank in the water line just before it goes into the loo; easy to source in any chandlers. I have one in my system to stop the pump turning on and off every time the tap is opened.

 

[jfm]

I'm not going through the domestic pump. That's the whole idea. The take-off will be before the pump and therefore not on the pressure side so the toilet will do all its own pumping and won't know it is pulling out of the tank rather than the sea.

OK fair enough. You were only asking "is this normal?".

You might want to consider whether your proposal sufficiently insulates the fresh water in the tank from the WC bowl. Sounds to me like you will have no valve twixt WC and tank and that the ecoli and other critters can just swim along the pipe past the pump impeller and into the tank. Or fall there if the bow lifts on a wave or if the tank is lower than the WC flush nozzle. Maybe there is a component that prevents that - I do not know what the instructions say or what you have in the kit of parts.

 

[jfm]

Just a thought: If you already have a pressurized water feed to your heads, why not fit a small plastic accumulator tank in the water line just before it goes into the loo; easy to source in any chandlers. I have one in my system to stop the pump turning on and off every time the tap is opened.

As I read it rustybarge he is not taking the WC flush water from the pressurised domestic water system

 

[rustybarge]

As I read it rustybarge he is not taking the WC flush water from the pressurised domestic water system

ah yes, but it will save him running a new pipe from the tank to the heads, the accumulator tank will supply plenty of pressure and volume to the 'flush'.

 

[adey]

You'd need to make very sure that the one way valve is up to it. You don't want any bacteria entering the fresh water system. A separate tank might be an idea?

 

[jfm]

ah yes, but it will save him running a new pipe from the tank to the heads, the accumulator tank will supply plenty of pressure and volume to the 'flush'.

I know, and that is how mine are always plumbed, but OP (PCUK) is adamant he doesn't want to!

 

[PCUK]

All right, I give up, we're just going round in circles. I'll do it my way (as Francis Albert used to say!)

 

[superheat6k]

Not familiar with the specific model, but I have just converted one of my loos to FW flush. Mine is the older Jabsco hand pump loo with an electric conversion. This is what I did ...

1 Removed FW impellor from flush pump & disconnected the sewater supply.
2 Plugged the bypass water lubricating supply to the upper impellor from the lower macerator assisted poo pump.
3 Installed the solenoid feeding directly to the loo inlet connection, via a syphon break bend several inches above the loo level. This provides an air break. When the loo has been flushed the last section drains into the loo, this stops any chance of nasties migrating back into the fresh water system.

Works really well and no more smelly loo.

Got the parts to do the other loo but it was a **** of a job - no particular reason for this just everything about it was unnecessarily bloody difficult, so now waiting for the enthusiasm to build up sufficiently to tackle the second one.

 

[MapisM]

This is what I did...

Fwiw, I would definitely prefer your solution, but each to their own...

 

[PCUK]

Many thanks Superheat. The anti-syphon loop is a sensible belt and braces step that I can incorporate. And thanks too everyone who has contributed to the discussion. I'll report back from my bed in the tropical disease unit when I've finished the job.:nonchalance: