Anti-syphon loop - how high?

[gabosifat]

Hi Everyone,

I'm doing the same project as Sean on my E35/3, namely re doing the whole sanitation system with new holding tank and lines. Question - how high should the anti-syphon loop be placed? Sean's was put high up under the sink on the plywood pad which looks as though it was designed for it originally. On my boat, the previous owner had brought the loop up into the back of the locker with sliding doors behind the toilet. The loop was way up just under the deck level. This destroyed the use of this locker as it had 3 sections of 1 1/2" lines plus the vent line. I guess my question is does heeling make a difference to how high the loop should be installed and am I safe to put the loop in the back of the sink locker?

Many thanks,
Steve Gabbott
E35/3 Silent Dancer
Vancouver

 

[Loren Beach]

By the time they built our boat in the fall of '88, they did not not use any loops or anti-syphon fittings.
When I rebuilt the whole system with all new hoses and new valves, etc, I did not put any "loops" in it.

As a general precaution we do close both head thru-hull valves when we are off the boat.
Additionally, while I have heard of failures on the intake check-valve side and sometimes seepage back from the output check-valve ("joker") I have never heard of a catastrophic failure of either of these.

I once found that the bowl was almost full, when performing a 3 am potty inspection, though... it only takes a little scrap of paper in the joker valve to let sea water trickle back in. Just another reason to always pump the head 10 times before setting it back to "dry bowl."


Loren

 

[PDX]

Loren

I'm not familiar with the layout of your boat at all, but if the toilet is above the water line then all those loops are supposed to be unnecessary. Our boat (1968) didn't have any either. We learned quickly to keep the (gate) valves closed unless we were flushing.

 

[Ray Rhode]

Steve,

On Journey the head discharge goes directly to the holding tank which is vented. There is no way that there can be any syphoning through the 1 1/2 inch line. Even if the overboard dischage thru hull is open the tank acts as an anti-syphon. For the intake line I believe that the sharing of the thru hull with the sink drain will prevent any syphoning. I do not have anti-syphon vents on any lines in the head and have not had any trouble for the 10 years we have had Journey.

Also there are no anti-syphon vents shown in the owners manual.


Ray Rhode
S/V Journey
E34-III, #189

 

[Frank Langer]

Ray,

From your description I understand that you would not get siphoning between the head and the holding tank, but would it not still be possible to get siphoning in the intake hose from the thru hull into the head if the seacock is left open?

Frank

 

[Emerald]

Heads flooding/sinking boats is not uncommon. The head is often very close to the water line (and even if above at the pier, it may be well below heeled over), and if the seacock for the intake of water for flushing is not closed after use, you are relying on the valve in the intake/pump mechanism of the head itself to keep the seawater out. So, to start, best practice would be to only open this seacock when actually flushing. With the realization that things don't always get closed, we have guests/children etc., it is indeed a very good idea to install a vented loop between the seacock and water intake to help prevent flooding. For the loop to be effective, it must be above the waterline, and this means at all times, so yes, heeling does make a difference. I am not familiar with your layout to comment on where the loop should be placed, but it sounds like the placement in the cabinet below decks may have been scoped out as the point of minimum height to cover heel angle and be out of sight. Generally, the closer to midships the better on installation of something like this, so the variation of height due to heel is minimized and therefore maximum height above the waterline is maintained.

Hope this helps with the placement.

 

[Glyn Judson]

To vent or not to vent.

Steve, Here's what I did with our head system, essentially starting from scratch aside from the framework for the holding tank, just what you're facing. I bought an exact replacement holding tank to the original from Ronco Plastics http://www.ronco-plastics.com/, the same outfit that made them for Ericson when our boats were new. You could build a platform for whatever tank you select but I'd suggest making it from 3/4" plywood if not well supported across the bottom. Mine's well supported and I still replaced the 1/2" plywood with 3/4". I used 1X2's glued and screwed into the edges of the plywood and have a wood strap anchored to the underside of the V-berth across the tank top to keep it in place. If/when you order a tank, consider asking to have a 3" threaded deck plate added to the top, you may never have to use it but it'll be there should you need to take a garden hose to the inside. Our head is situated such that it faces aft and it was no trick to route the discharge hose through the bulkhead separating the head from the V-berth to the Ronco tank. But more importantly the lip of our head is about 1/4" above the outside waterline, waay too close for my comfort. Fortunately due to the layout of the head compartment, I was able to route a reinforced vinyl raw water intake hose from the seacock under the sink, behind the toilet and up the bulkhead to about standing chest height where it attaches to a 3/4" bronze Groco vented loop, all of which is hidden in the corner of the compartment by a bath towel on a hook above it. A vinyl hose leads from the loop to the raw water barb on the toilet. The idea of placing the loop there was to get it higher than the waterline even on a significant heel. Additionally, it's almost on the centerline of the boat (over the keel), the best possible location. But by placing the loop in that part of the raw water circuit, the loop vent will never get pressed closed by water being pushed past it, quite the opposite, it's PULLED past the vent when the head pump handle is used. So the only way to get water past the loop is to seal off the vent hole with a finger tip while pumping. When finished pumping the bowl clean, the finger tip is removed and the intake hose allows the water raw water to return to the outside waterline level, well below the loop above. By routing the hose that way, there is virtually no way the toilet could ever syphon water and over time, sink the boat. A friends E31 with the same Groco K-H head as mine ended up with the bowl 1/4" below the water line and almost sank the boat in its slip twice in two weeks by forgetting to close the seacock as he thought he'd disciplined himself to do. I can't think of anything else to offer so I hope this helps, Glyn Judson, E31 hull #55, Marina del Rey, CA

 

[Glyn Judson]

Head plumbing.

Steve, One more thought. Do consider laying out your plumbing after the West Marine "Our Favorite Method" found in their West Advisor section near all the heads. Also consider replacing the Y-valve #8 with a simple T fitting as the Y-valve really serves no purpose and makes the use of the system much simpler. Go for it and send us photos as you go. Glyn

 

[Ray Rhode]

Steve,

I understand the concern expressed by you and the others but I have had this arrangement for 10 years and have been heeled to port pretty far and have never had a problem. I believe that the fact that the thru hull is shared with the sink drain is the explanation. When heeled the water finds less restance going up the sink drain than it does getting past the "check valve" formed by the head intake pump. As long as the head presents more resistance than the height of the water column in the sink drain there should be no syphoning.

I could be all wet (pun intended) but it has worked for me and as I pointed out in my first response I see no anti-syphon vent in the plumbing diagram in the owner's manual.

Ray

 

[Maine Sail]

I was able to route a reinforced vinyl raw water intake hose from the seacock under the sink, behind the toilet and up the bulkhead to about standing chest height where it attaches to a 3/4" bronze Groco vented loop, all of which is hidden in the corner of the compartment by a bath towel on a hook above it. A vinyl hose leads from the loop to the raw water barb on the toilet.

All good points but vented loops/siphon breaks, should generally be placed in the pressure side of a pump, not the intake side. This is why you need the finger tip method..

The vented loop should be placed between the head pump outlet and the bowl inlet by removing the small factory plastic hose that leads from the pump output around the back of the bowl and replacing it with the high point and vented loop. This is a very common mistake people make.

Vented loops/siphon breaks let air into a standing column of water, under the vacuum created by the weight of the standing water in the hoses, to break a siphon. They also allow air into the system while pumping thus reducing performance, or in your case requiring a finger, and why they are not intended to be used on any suction line. They seal on pressure break on vacuum/suction.

In answer to the OP, as high as possible is best. They can only break a siphon if they remain above the waterline on all points of sail..

 

[Glyn Judson]

Where should my vented loop be located?

Well gosh, what can I tell you? Years ago after coming up with the idea of using the 3/4" Groco loop backwards so to speak, I contacted Tim at Groco (wonder if he's still there?) who not only confirmed that my plan would work but that it's exactly the recommended method of installation he has folks do for that absolute safety measure against syphoning. I know the vent should be on the pressure side, that's the whole point of placing a finger over the vent hole when pumping in my installation, otherwise it would never work. Furthermore, not all heads have a convenient little plastic hose for one to pop off to add a loop to. Mine was not a common mistake, it was deliberate, the Groco model K-H and others such as the Wilcox Crittenden Skipper have no external hoses. Please see the link here: http://www.groco.net/SVC-MAN-07/Sec1/pdfs/K.pdf and you'll note that the inlet is a bronze plate and bronze barb, with no external plastic hoses to be found. My way is the ONLY way to use a vented loop in the circuit of a K-H and some other heads that is guaranteed to prevent syphoning as soon as the finger tip is taken away. Glyn Judson, E31 hull #55, Marina del Rey, CA

 

[Mark F]

I do not have a vented loop on my head plumbing. The head sink drain is connected to the raw water intake for the head. What I have found is that I can fill the sink before using the head then wash my hands in the sink and use that (fresh) water to flush the head. I never have to open any through hulls and I'm using fresh water for flushing.

 

[Maine Sail]

Well gosh, what can I tell you? Years ago after coming up with the idea of using the 3/4" Groco loop backwards so to speak, I contacted Tim at Groco (wonder if he's still there?) who not only confirmed that my plan would work but that it's exactly the recommended method of installation he has folks do for that absolute safety measure against syphoning. I know the vent should be on the pressure side, that's the whole point of placing a finger over the vent hole when pumping in my installation, otherwise it would never work. Furthermore, not all heads have a convenient little plastic hose for one to pop off to add a loop to. Mine was not a common mistake, it was deliberate, the Groco model K-H and others such as the Wilcox Crittenden Skipper have no external hoses. Please see the link here: http://www.groco.net/SVC-MAN-07/Sec1/pdfs/K.pdf and you'll note that the inlet is a bronze plate and bronze barb, with no external plastic hoses to be found. My way is the ONLY way to use a vented loop in the circuit of a K-H and some other heads that is guaranteed to prevent syphoning as soon as the finger tip is taken away. Glyn Judson, E31 hull #55, Marina del Rey, CA

Glyn,

With that head there are few choices. Another option I have seen used is a ball valve used under the Scot type siphon break. This way you don't need the finger tip. Personally I would prefer the finger tip as you can't forget to re-open the valve. A few folks I know with those heads have put an in-line valve right before the inlet but again you need to remember closing it.

I was not suggesting that the finger tip method does not work but rather pointing out the operation of a vented loop. You obviously already understood how they work but many boaters don't.

I have even seen boat yards install them on the suction side of a raw water pump. The pump can over come the air, and will move water, but often has dry periods and short impeller & pump life..

 

[Emerald]

Hi Mainsail,

good reminder on the placement of the vented loop and how it works. I know this, and have to kick myself for not being clearer. It's easy to forget (how often does the average person deal with this?), and as already shown by Groco's/Glyn's method, there are subtle variations that are used/necessary depending on the exact equipment in place.

Another good discussion

 

[gabosifat]

One of the other reasons I ask is that I have had a couple of other occasions when we were well heeled on a starboard tack. I went down below to get something and looked in the head to see the sink absolutely flooding over the counter and pouring in the lockers behind the head. And I mean it was an impressive amount of water! Needless to say I closed the sink drain.

Thanks for all who responded to my enquiry.

Cheers,
Steve Gabbott
E35/3 Silent Dancer
Vancouver

 

[Loren Beach]

A high loop indeed

No syphon, but I just did a delivery on a lovely custom Jason 35, where the exit hose from the head was led up the bulkhead to a high loop. High as in about 2 or 3 feet above the seat!
The owner said that he understood that the purpose was to give the effluent a good downhill glide into the holding tank (and prevent any back surges from said h.t.

This was one of those spendy older bronze Groco's with the tall pump handle. No clogs!

Anyhow, just another data point for this thread...