Do I need a vented loop?

Sy-Revolution

Sy-Revolution

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I'm installing a holding tank, the heads (electirc mascerator) is above WL and so is the bottom of the holding tank (just), at preset I have no vented loop fitted, just a pipe coming up to the bog and one going straight out both skin fittings below WL. All seems to work fine. I have bought a Jabsco pump to pump out the holding tank, on their literature they say that if the outlet skin fitting is below WL then one has to fit a vented loop at least 20cm above WL at all angles of heel/trim.


I'm going to find it hard to fit one in so is it nessesary and if so why, when without the holding tank my system works just fine?

Alternatively I could plumb in a skin fitting outlet above WL, has anyone done this? If so is there a staining problem on your gelcoat?

Cheers,

Crispin
 
If you do need a loop heres how you make one-using copper plumbing fittings-a T 15mm in and out(or whatever size suites your piping) with a reduced take off of bottom of T of 8mm/10mm(microbore central heating) Take the microbore pipe up above water line or fit some plastic pipe to it if easier to thread. To create enough of a vacuum for system to work but allow air in to stop syphoning all you do is crush the microbore pipe with a pair of strong pliers. Cost max £5 uk(say $10) in bits if you dont have them around.
Phil
 
In my present setup there's no syphoning because there's an air gap in the toilet bowl. There's going to be a breather on the top of the holding tank so there's a vent there. The mascerator is just at WL. Hence I can't see why there's a need for a vented loop......
 
That's right. In effect the tank is the loop and its vent will therefore be the loop vent.

My loop doesn't have a vent. The loop can only siphon if the joker valve fails or is wedged open. You would know that anyway as the toilet bowl wouldn't empty. I assume the macerator has some sort of check valve on its downstream side?
 
Surely if you don't have a vented loop and you shut off the seacock then the gases in the holding tank will expand and cause a problem somewhere, quite apart from the siphoning issues?

FWIW all our heads, galley sinks etc. discharge above the waterline. Not sure if being a cat makes it any different, but it seems inherently safer to me, and improves flow. There is slight staining, though not serious.
 
<<< Surely if you don't have a vented loop and you shut off the seacock then the gases in the holding tank will expand and cause a problem somewhere >>>

The holding tank has its own vent, normally taken to somewhere high up on the topsides. It wouldn't work otherwise, as pumping into it with the seacock closed could burst the tank and create a nasty mess in the boat! So no need for another vent in the loop.

Discharges above the waterline tend to fill the dinghy! I don't fancy having mine full of heads discharge, but if that's your pleasure.....
 
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Discharges above the waterline tend to fill the dinghy! I don't fancy having mine full of heads discharge, but if that's your pleasure.....

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Good point - I must add this to my lengthening list of catamaran advantages; all our discharges are of course discreetly arrayed on the inner side of the hulls!
 
I seem to remember part of the reason for the anti-siphon loop is to stop the water in the bog siphoning in to the holding tank and leaving the bowl completely dry and possibly allowing smells back through, could be wrong.
I'm looking into fitting a tank myself this year.
 
Leomagill - if you do fit a tank, don't have the system we have, whereby the waste always goes into the tank, then out again by gravity. It blocks occasionally when the system is 'open' and blocks more often when it's opened after being closed.

I've fitted a Y valve for direct discharge most of the time which helps. The only problem is the only 1.5" Y valves I can find are Jabsco's with rather weak handles - you have to operate them regularly to prevent seizure.

If I was doing it from scratch I'd have 2 thru-hulls - one for direct discharge and one for the holding tank discharge, and I'd have a pump for emptying the tank. And I'd use good strong valves even if it meant not using Y valves.

I think a tank full indicator is helpful too - it's horrible when the vents get full of poo. I was looking for them the other day and see leesan.com do a couple of types.
 
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Exactly the system I'm installing. Y valve marked Pee & Poo /forums/images/graemlins/smile.gif

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Good! Have you been able to find decent Y Valves? I have another head to convert and am still on the search.
 
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