Intake vented loop

[Maine Sail]

Peggy,

What are your thoughts on intake vented loops for the Groco Model K or WC heads with no way to plumb between the pump & bowl?

 

[Peggie Hall HeadMistress]

Not designed to need one

And installing a vented loop in the intake line will prevent the pump from priming, so don't.

However, it's just about become a non-issue, 'cuz the Groco Model K Groco Model K instructions is the only one of this design still in production in the US...the Groco EB and the W-C Skipper, Imperial were discontinued long ago. You can't even get parts for most of 'em any more except for rebuild kits...and even those are being gradually phased out.

The only manual toilets left are the entry-level compacts (Jabsco, Thetford "Comfort Mate," and Groco HF), the highe quality Lavac and the Raritan PH II, PHC...everything else today is electric now. You can even put a motor on the Model K and the PH II, but I don't recommend it.

However, that doesn't mean that electric toilets don't need intake vented loops...most do if the toilet is installed below waterline. If the loop can't be installed between the pump and the bowl, an electric solenoid valve replaces the passive air valve.

 

[Stu Jackson]

Peggy,

What are your thoughts on intake vented loops for the Groco Model K or WC heads with no way to plumb between the pump & bowl?

Is having it visual in plain sight not an option?

 

[Peggie Hall HeadMistress]

Nope...

And I can't see how being able to see it would make any difference in whether it's needed or not.

If you'll look at the drawing in the link I posted for the Groco model K, you'll see that those toilets don't work the same way the typical piston cylinder pump does...the intake is separate from the discharge pump, spring loaded and operated by a foot pedal. You want flush water, step on the pedal to open a real valve, not just a flimsy little cam. You want "dry bowl," take your foot off the pedal and the intake valve closes completely, so there's no siphon going. No siphon, no vented loop needed.

 

[gettinthere]

I added a vented loop to my PHII.
But I'm curious, it hasn't had one since 1985. Why has this sailboat done OK for so long?

What are the conditions that would lead to problems of flooding?

 

[Peggie Hall HeadMistress]

I added a vented loop to my PHII.
But I'm curious, it hasn't had one since 1985. Why has this sailboat done OK for so long?

Luck...and/or a skipper who's religious about closing thru-hulls when he leaves the boat.

What are the conditions that would lead to problems of floodinANg?

Bringing flush water into most manual toilets requires pumping to PULL water into the bowl...that starts a siphon. Cloising the wet/dry valve blocks it but doesn't break the siphon...that's what a vented loop does. In the absence of a siphon breaker (vented loop), if the wet/dry valve is left in the wet mode and the intake thru-hull is also open, the siphon started by priming the pump will continue pulling water in till it sinks the boat unless you happen to be aboard to notice that your feet are getting wet.

The vented loop actually serves TWO functions...it's a siphon break AND it puts an arch in the line that's far enough above the waterline to keep water out of the bowl--and therefore the boat too--if the toilet is left in the wet mode when the thru-hull is open.

 

[gettinthere]

Cloising the wet/dry valve blocks it but doesn't break the siphon...that's what a vented loop does. In the absence of a siphon breaker (vented loop), if the wet/dry valve is left in the wet mode and the intake thru-hull is also open, the siphon started by priming the pump will continue pulling water in till it sinks the boat unless you happen to be aboard to notice that your feet are getting wet.

Peggy

I had the boat 2 years before installing the vented loop. I suspect the wet/dry valve was left open at some point in the 2 years, at least for a short time and the intake valve was almost always left open. Yet I saw no flooding. Is this a very slow process?
I assume the bowl would only fill up to the waterline? Perhaps the bowl sits higher than I think and therefore I wouldn't get flooding?

 

[Peggie Hall HeadMistress]

Waterline relative to bowl definitely matters...

Or a "hump" in the intake line could prevent it...UNLESS you'd been unfortunate enough for wind conditions to create a "following sea" while the boat was sitting in the slip with no one aboard...Iow, wind pushing water up a line through an open thru-hull. I've seen that sink more than one boat, not necessarily via the head intake thru-hull. It was wind that sank a friend's boat in its slip when he forgot to close the generator water pump seacock when he went home. He was in the middle of doing some work on it and had the hoses off when he had to leave on a Sunday. Monday night the wind came up from the "wrong" direction and blew most of the night....Tuesday morning he got a call from the YC telling him the bad news. Had the wind blown from any other direction it wouldn't have happened. Luck often makes the difference. You installed the loop before yours ran out.

 

[Ron20324]

I sometimes wonder why they call for a vented loop between the pump and the bowl... it seems as likely that the pump itself could crack and flood the boat.

 

[Head Master18695]

Not nearly as likely, although it is still possible. If the pump leaks, you may get some water in, but generally not nearly enough to sink the boat. The reason you are instructed to put the vented loop between the pump and the bowl, is that if you put it between the through-hull and the pump, you will draw in air when you pump the head, and won't bring in any water - the pump won't prime. With the vented loop on the output side of the pump, it won't affect the pump's ability to prime, but will still offer you a good deal of safety.

Sure, if the pump were to crack,or a hose come off, or a seal in the pump fail, you could still get unwanted water into the boat but again, USUALLY not enough to sink the boat, unless it is left unattended for weeks at a time. In that case, simply turn off the seacock at the supply water through-hull before leaving the boat (that's why it's there), and you're as safe as you can possibly be.