Vented Loops

PowerSlapper

PowerSlapper

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I am having a new head installed and the installer is insisting on fitting vented loops in both the inlet and discharge lines even though the original installation does not have them (and never had a problem with bowl flooding even though the bowl is below water level) I have heard some horror stories of the vents leaking resulting in poo and/or seawater dribbling into the heads compartment and the associated pong.
HWMO is not in favour of wasting money (~£100 on top) for something that is "liable to leak and is of dubious benefit" so what is collective experience of the "brethren" ? To fit or not to fit? I can see the benefit of breaking the possible siphon but I am worried about possible leakage from the vents.

Confused and worried at sea
 
Our boat didn't have a vented loop and there were no problems and our bowl was underwater too. If the fitter insists on a vented system get him to fit the loo but fit the pipe yourself, if he refuses find another fitter and tell him what you want.
 
A professional installer would be remiss not to put a vented loop in the outlet. They'd be daft to put them in the inlet if by "inlet" you mean between seacock and pump. For installations below the waterline the "inlet" loop should go between pump and bowl which often requires drilling more holes as mass-produced boats invariably have a short pipe between pump and bowl. Look at an upmarket swedish boat (e.g. Nauticat/Najad) and they always have it done "properly".

Some years ago I asked jabsco if the loop between pump and bowl was necessary. They said yes. Will you sink if you have a short pipe? Probably not, but can't blame the installer for insisting on it.

I've never had any problem with my vented loops. Make sure the clips are done up properly :-)
 
laika said:
A professional installer would be remiss not to put a vented loop in the outlet.
Click to expand...

And the inlet, between pump and bowl, if its jabsco or similar.

In many respects the inlet vent may be more important that the outlet. At least the outlet probably has a Joker valve and if its a Jabsco a "twist and lock" pump. There is no check valve on the inlet, just the little weighted valve in the pump head, to stop it syphoning if the seacock is left open

You dont have to worry if the kids or a visitor fails to shut the seacocks if the vented loops are fitted.

£100 sounds a bit excessive but even that is nothing compared to the trouble you'll have if you wake up one morning and find the water almost up to the bunk tops. .... It happened to someone I know when one of his children did not shut the seacocks.
 
I fitted both 'cos the Jabsco installation instructions said so. The real risk is if the bog level is below the waterline I think.
 
Thanks all, it is the latest Jabsco "twist and lock", the bog is well below water level and the FM does say fit in BOTH lines so I guess we might go along with the manual and other erudite opinions. If the vents leak and pong I can always seal them up with a dab or two of sikaflex.
 
PowerSlapper said:
Thanks all, it is the latest Jabsco "twist and lock", the bog is well below water level and the FM does say fit in BOTH lines so I guess we might go along with the manual and other erudite opinions. If the vents leak and pong I can always seal them up with a dab or two of sikaflex.
Click to expand...

But note the inlet loop replaces the short hose normally supplied between the pump and the bowl. If you fit it between seacock and pump you'll just suck in air instead of flush water.
 
Thanks Vic, I just read the other thread and then I RTFM and note the location of the inlet vent.
As a point of interest what stops salt water and poo water spraying out off the vent when pumping the bowl out?
I thought there was some sort of valve preventing water out but allowing air in to break the siphon effect but it seems it is just a small hole
 
PowerSlapper said:
Thanks Vic, I just read the other thread and then I RTFM and note the location of the inlet vent.
As a point of interest what stops salt water and poo water spraying out off the vent when pumping the bowl out?
I thought there was some sort of valve preventing water out but allowing air in to break the siphon effect but it seems it is just a small hole
Click to expand...

They should have a valve.

Example: http://www.force4.co.uk/force-4-1-1-2-vented-loop.html?sqr=vented loop&
 
Got it. Commercial ones have a proper valve, Bodger ones are simply a small hole either in the pipe or in the end of a bic type pen which is pushed into a larger hole in the pipe
 
PowerSlapper said:
Thanks Vic, I just read the other thread and then I RTFM and note the location of the inlet vent.
As a point of interest what stops salt water and poo water spraying out off the vent when pumping the bowl out?
I thought there was some sort of valve preventing water out but allowing air in to break the siphon effect but it seems it is just a small hole
Click to expand...

The Jabsco ones should have valves fitted, although replacement valves are also available ( in packs of 2).

The only non-valved antisyphon loop which comes to mind is the non- valved version of the Vetus ones which are commonly used as antisyphon devices in engine cooling water systems,

lpdsn's link shows the Jabsco type c/w valve. They come in three sizes 19mm (¾"), 25mm (1") and 38mm (1½")
 
PowerSlapper said:
Got it. Commercial ones have a proper valve, Bodger ones are simply a small hole either in the pipe or in the end of a bic type pen which is pushed into a larger hole in the pipe
Click to expand...

The "end bit of a Bic pen" type are the vents for the inlet pipe on Lavac toilets.
 
Last edited:
VicS said:
It happened to someone I know when one of his children did not shut the seacocks.
Click to expand...

Any toilet installation where you have to routinely open and close seacocks to prevent flooding is defective in my opinion. Yes, I know there are quite a few of them about.

Mine stay open year round with complete confidence, except for occasional exercising to prevent them seizing up.

Pete
 
prv said:
Mine stay open year round with complete confidence, except for occasional exercising to prevent them seizing up.

Pete
Click to expand...
That's what I like; confidence. We're much the same, though I have been known to close the outlet. I have to take half the aft cabin apart to get at the inlet, to which I fitted a vented loop.
 
prv said:
Any toilet installation where you have to routinely open and close seacocks to prevent flooding is defective in my opinion. Yes, I know there are quite a few of them about.

Mine stay open year round with complete confidence, except for occasional exercising to prevent them seizing up.

Pete
Click to expand...

Same as ours. We haven't sunk yet. (Or ever had a siphon)
 
KellysEye said:
>Our boat didn't have a vented loop and there were no problems and our bowl was underwater too.

To make it clear there was a very long loop about 5 feet high way above the waterline.
Click to expand...
That's not enough to prevent syphoning; it would have to be something like 30ft I think.
 
johnalison said:
That's not enough to prevent syphoning; it would have to be something like 30ft I think.
Click to expand...

Indeed.
It's easier in metric: around 10m, obviously depending on atmospheric pressure.
KellysEye's loop would be fine if he could find a partial vacuum to sail around in, although his sails wouldn't work very well. Couldn't make a decent cuppa, either ;)
 
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