Marine Plumbing Anti-Siphon Vent

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Mar 26, 2012
3
Hunter 30 Edgecomb, Maine
I'm overhauling my first sailboat bought and sailed a bunch of times last summer. A 1981 Hunter 30, in good shape for the deal I got but needs some TLC.

I'm replacing the head, and all associated plumbing including the lever/hand pump. (I'm also replacing most wiring, fresh water plumbing (will be cold only), running rigging, ...more posts likely!)

My current head setup is the toilet pumps strait to the tank. Out of tank is a tee, one side up to deck connection, other to the hand-pump a few feet aft. After the handpump is a loop above the waterline with an anti-siphon vent, then down and ovbd thru an 1-1/2" hull valve.

I plan on replacing the tee with a wye valve, one side to deck conn, other thru a new macerator pump and then ovbd.

I read some about the possibility of siphoning seawater back into your tank, so I figure it was there for a reason and I'd replace the vent.

So I bought an 1-1/2 bronze vent and enough 1-1/2 sanitation hose to do the job, then realized the macerator pump outlet is 1", so I'm going to swap the vent with the right size if I need it. I was going to go from 1" hose to an adapter for the 1-1/2 hull valve (rather than going to 1-1/2 right after the pump), I figured it would pump better maintaining the flow velocity/pressure with the smaller 1" hose.

I was comparing notes with a buddy who has a Catalina 30. He says he doesn't have an anti-siphon vent and goes strait ovbd from the pump outlet. He showed me original catalina parts list with this arrangement. He says just close the hull valve right after pumping and that will prevent any siphoning...

I was curious on your thoughts about the need for this vent at all, or the loop above waterline, and if on the size exchange whether a plastic one (i.e. less $) is good enough.

Also, I'm new to the forum (new to sailing...) and saw in someone's comment that for some reason Shields sanitation hose was not as good as Trident. I just bought what I needed (Shields) from my local marine supply (in Maine). I hope it's good enough for me, what's your thoughts about that?

Thank you so much for anything you can provide.
 
Mar 29, 2012
11
Sabre 28 Chestertown, MD
I hope I am not committing a major faux pas by piggybacking here, but since my question is VERY similar to yours, I thought I would ask for clarification here, rather than have Peggy reiterate on a seperate post. I too am new to sailing (and to forums, hence not sure about proper Etiquette) I recently purchased a Sabre 28 in need of a head overhaul (currently an illegal overboard only sys.) and need clarification on anti-siphon venting. In addition to your question, Huntah Ownah, I would like clarification on the need for anti-siphon venting between intake through hull and head. In the drawings I have seen, there are TWO anti-siphon vents. One on the intake side and one on the pump out side of the system. I thought this info may be helpful to you as well. If not, I appologize for infringing on your post. Adding my thanks for any help or insight you may offer.
 
Mar 26, 2012
3
Hunter 30 Edgecomb, Maine
On closer inspection of my boat, I know the head was replaced in about 2001, and the inlet went straight to the head...which explains last year why my head was nearly overflowing at times...!

I think my buddies head must be just above the waterline.

The instructions with my new head show using a vent on both in and out. I am "doing it right" and replacing both...

good luck!
 
Mar 27, 2012
312
Seaward Fox Washougal WA
On closer inspection of my boat, I know the head was replaced in about 2001, and the inlet went straight to the head...which explains last year why my head was nearly overflowing at times...!

I think my buddies head must be just above the waterline.

The instructions with my new head show using a vent on both in and out. I am "doing it right" and replacing both...

good luck!
How did it work out? I am new owner of 1984 H27 and starting same project. My head works fine, but when I pump out tank, the head overflows with river water. I have the same set up you explained prior to your project.

Thanks,
JB
 
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