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  #1  
Old 10-16-2008
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Anti-siphon in head supply hose?

I'm re-doing the hoses for the head (fun job). The boats I am familiar with have not had a vented anti-siphon in the supply hose to the head, it just runs straight from the seacock to the head. After checking Nigel C's book, it looks like there should one. My question is how would that work? If you have a vented anti-siphon (air in the hose at the loop) how are you going to develop any vacuum at the pump in the head (PHII) to draw any water in, seems to defy the laws of physics? What am I missing here? Do your systems have a/s before the pump on the supply? Thanks, I only want to do this once .

John
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Old 10-16-2008
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I've never seen an anti-siphon on a supply; only the discharge loop.
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Old 10-16-2008
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John,
I agree with you that an anti-siphon doesn't make much sense. My head has a check valve in the supply line which is supposed to prevent a loss of prime not encourage it. Perhaps that is what Nigel's book is refering to. I also have a Lectrosan with a salt tank. There's a small line from the check valve to the salt tank, but it's not open to the air.
Bill
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Old 10-16-2008
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You don't put the anti-siphon on the supply line—which is why you've never seen it before.

The one exception to this that I can think of is the Lavac heads...which have something that resembles a vacuum break on their supply line.
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Old 10-16-2008
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I have a anti-siphon valve on the salt vater intake on my toilet, as recomended by the manufacturere. The mounting instruction states that if the top of the bowl is below the waterline a anti-siphon valve is recomended.

the hose between the pump and the bowl is lead above the waterline with a 180 degree bend having at anti-siphon valve.

In practical use there is no water leaking from the valve, problems with suction is solved since the valve is placed after the pump.

I almost had a bot sink for me because there was no anti-siphon valve and we forgot to close the water intake when leaving thye boat.
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Old 10-16-2008
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Quote:
Originally Posted by sailingdog View Post

The one exception to this that I can think of is the Lavac heads...which have something that resembles a vacuum break on their supply line.
Yes! I have a Lavac head and an anti-siphon on the supply hose is necessary. On any other head, though, wouldn't you want an anti-siphon on the supply hose as well? Even if it is redundant it would be a nice security back-up. The hose fills with water from the thru-hull to the head so the possibility of siphoning water directly to your head exists.

As far as pumping water to the head past an anti-siphon it is no problem. The hole is not big enough for water to pass through, just big enough to bleed in some air to break the siphon lock created during pumping.
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I guess it depends on whether the top of the head bowl is below the waterline or not. If it is, an anti-siphon device would be a good idea, but on many boat's it isn't that low. On my boat, the head itself is mostly above the waterline...but that's probably because it's a multihull with a 15" draft board up.
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Old 10-16-2008
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It is simple!!

The anti-siphon valve goes between the outlet from the pump to the bowl.

You simply remove the little white factory hose that runs from the pump around the back of the toilet to feed and fill the bowl. Run your new hose from the pump to a nice high anti-siphon breaker and then back to the inlet to the bowl..

It does not go on the intake to the pump but rather the outlet of the pump and then you can't siphon water but can still prime your pump...


Here is the exact wording from the Raritan PH-II manual pg. 5:

WARNING: Below waterline installations
require vented loops. Top of the loop must
be above waterline at greatest angle of heel.

Intake vented loops must be installed
between pump and back of the bowl.
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Last edited by Maine Sail; 10-16-2008 at 02:41 PM.
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That makes sense... On my boat it could never siphon... the head is mounted about six inches above the cabin sole, and the top of the head is about 10" above the waterline...and I don't heel enough for that to matter.
Quote:
Originally Posted by Maine Sail View Post
The anti-siphon valve goes between the outlet from the pump to the bowl.

You simply remove the little white factory hose that runs from the pump around the back of the toilet to feed and fill the bowl. Run your new hose from the pump to a nice high anti-siphon breaker and then back to the inlet to the bowl..

It does not go on the intake to the pump but rather the outlet of the pump and then you can't siphon water but can still prime your pump...
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You know what the first rule of sailing is? ...Love. You can learn all the math in the 'verse, but you take
a boat to the sea you don't love, she'll shake you off just as sure as the turning of the worlds. Love keeps
her going when she oughta fall down, tells you she's hurting 'fore she keens. Makes her a home.

—Cpt. Mal Reynolds, Serenity (edited)

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Old 10-16-2008
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Just in case my post was confusing my anti-siphon also is between the pump and the head intake, just as Maine Sail explained.
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