Vented loop

[stu9000]

I have fitted a force 4 electric head
Force 4 Electric Sea Toilet 12V | Force 4 Chandlery
It replaces the standard push pull jabasco pump which was pretty old and very calcified in the bottom section.

It certainly isn't silent flush but isn't particularly intrusive. And the previous manual banging as the manual pump hit the end of its travel certainly was intrusive. I'm hoping that a button press will ensure a thorough flushing by users.

The existing set up has a vented loop on both the water in loop and the wider black water outlet hose.
I understand the value of avoiding having seawater siphon into the boat but is it required on the water in side?

The bowl is cited slightly below sea level but doesn't the electric pump prevent siphoning?
I would leave well alone but the pump has to run for several seconds to pull water over the venting loop. Not having a vent would meant the pump would prime more quickly.

This website seems to suggest a vent is not required on the water in side.
Y-Valves / Vented Loops / Check Valves -etc. - Vented Loop Q&A - Marine Sanitation & Supply

I'm also curious about the nut at the top of the loop. It seems to twist open and closed but air vents regardless.

Thoughts?

S

 

[Catalina36]

"The bowl is cited slightly below sea level but doesn't the electric pump prevent siphoning? "

No it won't. This much I know for a fact. Do not remove the vented loop on the intake.

 

[jiris]

The pump will prevent water from entering - for a while. But as the impeller gets worn a bit (and it won't take long), you will get a slow leak thru the intake. The loop is essential.

 

[LittleSister]

I would leave well alone but the pump has to run for several seconds to pull water over the venting loop. Not having a vent would meant the pump would prime more quickly.

This website seems to suggest a vent is not required on the water in side.
Y-Valves / Vented Loops / Check Valves -etc. - Vented Loop Q&A - Marine Sanitation & Supply

I'm also curious about the nut at the top of the loop. It seems to twist open and closed but air vents regardless.

I think -
1) you need a vented loop in the water supply to your toilet to be safe (or a conscious decision you are going to take the risk);

2) your pump should not be 'pulling water over the vented loop' (unless it is a Lavac, which anyway has a different sort of vent and pump), it should be pushing water past it. The vented loop should not be between the water inlet seacock and the pump, but between the pump and the toilet. It is when it is water is being pumped past it closes. It opens when the water pressure subsides below the air pressure outside, letting air in, the water level fall, and leaving an air gap at the top of the line thus preventing syphoning.

3) you have misread the website you link to (though to be fair that website is really badly written, and self-contradictory in parts - much better guidance is available elsewhere).
If you look at the diagram on that page, it correctly shows a vented loop on the water inlet side, between the pump and the toilet pan (and another on the waste outlet side, between the pump and outlet seacock).
The website text says 'If your toilet is below water line you would install the Vented Loop in the line between the toilet pump and the bowl. It would NOT go in the intake line.)'
Note that the whole of this quoted section of text addresses only the water inlet side of the system, not the waste outlet side (though it doesn't make this explicit). So when it says 'It would NOT go in the intake line.' it doesn't mean that you don't have to have one on the water supply side of the system, but instead that the vented loop on the water supply side of the system goes in the water outlet line from the pump to the bowl, not the water intake line to the pump from the seacock to the pump.
You can tell that this section is only about the water supply side vented loop, because the waste side vented loop would not go between 'the toilet pump and the bowl, but instead between the toilet pump and the outlet seacock (see the diagram).

4) the 'nut' at the top of the vented loop is (almost certainly) the non-return valve. There's probably a rubber disc or flap underneath. It is removable both for ease of manufacture and so that you can rinse out the valve from time to time to ensure it is not being prevented from closing by salt crystal or other debris. I expect the nut should be fully screwed down. If there were no pipes connected underneath the vented loop and you put your mouth (or a dinghy pump) over the valve you should be able to blow into it, but not suck out of it. (You can try that when you change the pipes around to put the vented loop in the correct bit of the water supply line! )

 

[Catalina36]

An alternative is to use fresh-water flushing and disconnect the seawater flush entirely.

 

[stu9000]

I think -
1) you need a vented loop in the water supply to your toilet to be safe (or a conscious decision you are going to take the risk);

2) your pump should not be 'pulling water over the vented loop' (unless it is a Lavac, which anyway has a different sort of vent and pump), it should be pushing water past it. The vented loop should not be between the water inlet seacock and the pump, but between the pump and the toilet. It is when it is water is being pumped past it closes. It opens when the water pressure subsides below the air pressure outside, letting air in, the water level fall, and leaving an air gap at the top of the line thus preventing syphoning.

3) you have misread the website you link to (though to be fair that website is really badly written, and self-contradictory in parts - much better guidance is available elsewhere).
If you look at the diagram on that page, it correctly shows a vented loop on the water inlet side, between the pump and the toilet pan (and another on the waste outlet side, between the pump and outlet seacock).
The website text says 'If your toilet is below water line you would install the Vented Loop in the line between the toilet pump and the bowl. It would NOT go in the intake line.)'
Note that the whole of this quoted section of text addresses only the water inlet side of the system, not the waste outlet side (though it doesn't make this explicit). So when it says 'It would NOT go in the intake line.' it doesn't mean that you don't have to have one on the water supply side of the system, but instead that the vented loop on the water supply side of the system goes in the water outlet line from the pump to the bowl, not the water intake line to the pump from the seacock to the pump.
You can tell that this section is only about the water supply side vented loop, because the waste side vented loop would not go between 'the toilet pump and the bowl, but instead between the toilet pump and the outlet seacock (see the diagram).

4) the 'nut' at the top of the vented loop is (almost certainly) the non-return valve. There's probably a rubber disc or flap underneath. It is removable both for ease of manufacture and so that you can rinse out the valve from time to time to ensure it is not being prevented from closing by salt crystal or other debris. I expect the nut should be fully screwed down. If there were no pipes connected underneath the vented loop and you put your mouth (or a dinghy pump) over the valve you should be able to blow into it, but not suck out of it. (You can try that when you change the pipes around to put the vented loop in the correct bit of the water supply line! )

Thanks. If I have this right I need to change how the head is plumbed.
Water In seacock to the pump then from pump over a loop to where it squirts into the bowl.
This isn't how it came out of the box but should be easy enough.

I won't be putting my mouth over any non return valve though.

Cheers

 

[stu9000]

The pump will prevent water from entering - for a while. But as the impeller gets worn a bit (and it won't take long), you will get a slow leak thru the intake. The loop is essential.

Thanks. I have read this elsewhere too.

 

[LittleSister]

Thanks. If I have this right I need to change how the head is plumbed.
Water In seacock to the pump then from pump over a loop to where it squirts into the bowl.
This isn't how it came out of the box but should be easy enough.

I won't be putting my mouth over any non return valve though.

Cheers

Yes. You need to change how the head is plumbed exactly as you describe.

The Jabsco and similar toilets are supplied with a short hose (about 1/2" or 3/4" dia IIRC) fitted between the pump and the top of the toilet bowl (where the water squirts in, as you say).

That is fine if your toilet is mounted wholly above the waterline. Otherwise (i.e. for most of us), you need to disconnect that short hose and plumb in a vented loop between the pump and where the water is squirted into the toilet. That vented loop should be mounted above the waterline (including the waterline when the boat is heeled, which may be easier near the centre of the boat), so you will need some extra hose to do that.

Apart from anything else, this will do away with the problem you mentioned previously of the pump struggling to suck water up the pipe when the vented loop you had fitted incorrectly before the pump (i.e. between it and the seacock) was allowing it to suck air instead.

Fitted after the the pump, the water pressure when pumping will close the vent, and it will only open when you stop pumping, allowing a little air in to break the potential syphon.

Hope you can now get sorted.