Vacu-flush water supply: Why vacuum hose?

[Mirage35]

The fresh water connection hose to my Vacu-flush has developed a pinhole leak. Temporary repair with self-fusing tape is holding but I will want to replace the hose.

The existing hose is vacuum rated, similar to the extraction hoses (but smaller, of course) that connect to the vacuum generator and holding tank. I don't understand why this would be necessary - it's just connected to the pressurized fresh water system, not the vacuum system.

Does anyone know why I can't replace this with a normal water hose of appropriate diameter?

[Montanan]

Albeit not knowing the mechanism of producing the vacuum, I will propose that the pressurized water is being used to power an eductor [a.k.a. a jet pump] to induce a vacuum to assist with the flushing action.

The issue with vacuum is that it literally sucks and one does not want anything to blow that.

[Mirage35]

It's actually connected by a tee joint to another line that goes to the water heater. So I think I'm answering my own question - if the two other hoses connected to the tee are okay with it then there's no reason why this one shouldn't be.

Vacu-flush toilets have a vacuum generator between the toilet and the holding tank, and those connections need vacuum rated hose.

[peghall]

All hoses in any sanitation system should always be marine sanitation hose. Plain ol' clear vinyl water hose will not last very long...You can use flexible PVC #148 (the cheapest) for this job.



--Peggie

[Windpilot]

I've had my 2 VF systems for 12 years now.
The fresh water "pressurized" line is not part of the vacuum system itself. It's basically on/off to flush and add water. There's also a vacuum breaker at the back of the head so no way it could ever suck anything back into the freshwater line.
Use normal/same hose.

[Mirage35]

Ah, the expert has spoken. That looks like a stock item at my nearest chandlery so it will be easy to give it a try - and cheap enough to keep a spare on hand.

[PJS]

I cannot speak to what your boat has for water supply lines (depends on age of boat) but I do know my boat, as well as many others, have essentially PEX water supply lines. I replumbed many areas with new PEX and have experienced no issues. Any capable person can (should?) be able to replumb with PEX and the proper tools & knowledge (reading and doing).
There are 3 types of PEX you can obtain from any box store.
PEX-A. PEX-a is flexible and has essentially no coil memory, making it ideal for expansion fittings.
PEX-B. PEX-b is the most commonly used PEX tubing in North America for over 40 years and typically carries a 25-year warranty.
PEX-C. PEX-c has less coil memory than PEX-b due to its manufacturing process.

PEX type C is the easiest to use as it can bend around all the areas that a line needs to be run in a boat
To Peg's point, it's a marine application, you want to ensure good crimps are made so there are no blowouts.
I run my system at 40 LBS of pressure and have experienced no leak issues with using PEX.

[Shrew]

Originally Posted by Mirage35

Does anyone know why I can't replace this with a normal water hose of appropriate diameter?

Because the vacuum pressure may collapse the hose. You want the force moving material, not constricting the inside diameter of the passage.

This applies to the hose going from the holding tank to the pump-out deck plate, and from the head to the accumulator tank. The hose from the accumulator tank to the holding tank and from the holding tank to a discharge macerator doesn't technically need to be vacuum rated, but most good sanitation line is vacuum rated anyway.

[peghall]

[QUOTE=PJS;3932508]I cannot speak to what your boat has for water supply lines (depends on age of boat) but I do know my boat, as well as many others, have essentially PEX water supply lines. I replumbed many areas with new PEX and have experienced no issues. Any capable person can (should?) be able to replumb with PEX and the proper tools & knowledge (reading and doing).[QUOTE


We're only talking about the flush water supply line for ANY toilet designed to use pressurized freshwater, which uses the same 3/4" sanitation hose as any other toilet except that instead of connecting it to a thru-hull, it's teed into the cold water line to the head sink.



--Peggie

[peghall]

Originally Posted by Shrew

Because the vacuum pressure may collapse the hose. You want the force moving material, not constricting the inside diameter of the passage.

This applies to the hose going from the holding tank to the pump-out deck plate, and from the head to the accumulator tank. The hose from the accumulator tank to the holding tank and from the holding tank to a discharge macerator doesn't technically need to be vacuum rated, but most good sanitation line is vacuum rated anyway.

The holding tank vent line and flush water intake line should also be sanitation hose. Even the cheapest flexible PVC #148, which is fine for use as a tank vent flush water intake line,is "vacuum rated" by the helix in it.

--Peggie

--Peggie

[Mirage35]

Thanks to all for the feedback. There are enough interesting leads on plumbing design to keep me amused over the winter should I decide to follow them, and enough specifics that relate to my system that I have confidence in my solution.

Now if someone can tell me how to grow longer arms so I can more easily get at the (*^% connector, that would also be helpful.

"Boat yoga" is what keeps us all young!