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Old 31-10-2015, 14:58   #1
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Anti-Siphon Loop for Raw Water Exhaust

I have a necessary anti-siphon valve on a loop that rises above the waterline carrying raw water from my exhaust manifold and back to the mixing elbow for my Yanmar 4JH3E. The top of my loop has galvanized pipe fittings with a nylon anti-siphon valve....


I discovered a patch of crusty salt where water had leaked from this failed valve. There is a plastic washer inside that a disc with an off-center hole for air passage is meant to be seated. I tried to cut a replacement piece, but the parts are too delicate for my skill. I've temporarily placed a toothpick in the top and covered it with the finger of a glove while running my engine.....


Of course, I remove the toothpick when I stop my engine to let air in.

My internet searches have only led me to the antisiphon valves with the little rubber "duck bill" valves such as those for heads and I'm not confident that they will stand up to the heat of my raw water exhaust. Other valves I've found are for faucets and sprinkler systems.

I have not seen them in my marine catalogs. Can someone tell me who has these simple anti-siphon valves for hot water exhaust?
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Old 31-10-2015, 15:03   #2
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Re: Anti-Siphon Loop for Raw Water Exhaust

This is what's on my 4JH3E. $65 from Defender.
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Old 31-10-2015, 16:44   #3
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Re: Anti-Siphon Loop for Raw Water Exhaust

Thanks Rick, I would rather have this than the galvanized pipe fitting too. This is likely my best choice.
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Old 31-10-2015, 17:24   #4
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Re: Anti-Siphon Loop for Raw Water Exhaust

Brass home plumbing vacuum break valves work OK too.

Sample : N36 Water Service Vacuum Relief Valves, Vacuum Relief Valves, Water Safety & Flow Control - Watts Canada
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Old 31-10-2015, 17:32   #5
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Re: Anti-Siphon Loop for Raw Water Exhaust

Why have a valve at all. Just take a small diameter tube from the high point of the loop and run it vertical for a couple of feet.

There is no real pressure in the raw water loop, the water will be pushed many a foot into the tube when running but will provide the siphon break when at rest.

There is the exhaust pressure to contend with but I have found that the tube can usually be taken high enough to cope.

Of course, YMMV.
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Old 31-10-2015, 17:48   #6
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Re: Anti-Siphon Loop for Raw Water Exhaust

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Originally Posted by Wotname View Post
Why have a valve at all. Just take a small diameter tube from the high point of the loop and run it vertical for a couple of feet. .......................
Excellent idea for ditching my toothpick, latex glove finger and rubber band! I'm still more than a week from remaining in a port for some time to decide on a fix. I have some Tygon tubing that will fit on the hose barb at this failed valve. This will save me from crawling in some tight hot spaces every time I want to stop my engine and I can judge whether I'd want to keep the plan.
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Old 31-10-2015, 17:59   #7
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Re: Anti-Siphon Loop for Raw Water Exhaust

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Originally Posted by Wotname View Post
Why have a valve at all. Just take a small diameter tube from the high point of the loop and run it vertical for a couple of feet.
Of course, YMMV.
Go even further and plumb that little line from the top of the loop somewhere. Some take it into the cockpit. I have 1/4" hose going to a small through hull high up on the side of the boat that I can touch sitting in the cockpit. As bonus not to be scoffed at, you can feel the water temp of your engine with your fingers. You can also tell more about the water flow from the pump by how much water coming out of the hose . It's not really that much water on our boat with a Perkins, more like a big dribble of warm water.
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Old 31-10-2015, 18:11   #8
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Re: Anti-Siphon Loop for Raw Water Exhaust

SCOT vacuum breakers, made from Delrin, would fit the bill:
http://www.scotpumpmarine.com/sn/SN-890-913.pdf
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Old 31-10-2015, 18:15   #9
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Re: Anti-Siphon Loop for Raw Water Exhaust

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Originally Posted by Vasco View Post
This is what's on my 4JH3E. $65 from Defender.


That is what is on my JH4E also.


S/V B'Shert
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Old 31-10-2015, 18:30   #10
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Re: Anti-Siphon Loop for Raw Water Exhaust

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Originally Posted by Vasco View Post
This is what's on my 4JH3E. $65 from Defender.


Mine are 15 years old. I recently replaced all the raw water hoses on both engines (volvos, in my case) and planned to replace these, too. However, they are n excellent condition and the little rubber bellows valves are in good working order. So I kept them. I was very impressed.


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Old 31-10-2015, 19:36   #11
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Re: Anti-Siphon Loop for Raw Water Exhaust

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Originally Posted by Guy View Post
Go even further and plumb that little line from the top of the loop somewhere. Some take it into the cockpit. I have 1/4" hose going to a small through hull high up on the side of the boat that I can touch sitting in the cockpit. As bonus not to be scoffed at, you can feel the water temp of your engine with your fingers. You can also tell more about the water flow from the pump by how much water coming out of the hose . It's not really that much water on our boat with a Perkins, more like a big dribble of warm water.
+1, One of my boats was setup this way, & it's a KISS way of knowing that your engine's getting what it needs in terms of cooling water, especially if you have, say, a center cockpit. Or the noise from wind & waves blocks out your ability to hear your engine's exhaust, & the raw water in it.
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Old 31-10-2015, 19:37   #12
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Re: Anti-Siphon Loop for Raw Water Exhaust

Aren't these valves meant tofu ction when the engine is off? If there is water coming out of the valve the the spring I the valve probably needs replacing
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Old 31-10-2015, 19:38   #13
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Re: Anti-Siphon Loop for Raw Water Exhaust

Good news for me! In the two hours since Wotname's post recommending the tube extension I've eaten supper, cleared things away, washed the dishes and added a 2.5 foot tube to my failed anti-siphon vent that leads to the top of my starboard cockpit locker. At this point I can observe that the head pressure will prevent the water from rising to this level or easily cap the tube without crawling into the far reach of my engine room after running.

Regardless of my final solution (and thanks for all the other ideas) I'm good for the next two weeks until I get a new part or decide to keep the extension tube.
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Old 31-10-2015, 19:48   #14
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Re: Anti-Siphon Loop for Raw Water Exhaust

Quote:
Originally Posted by neilsty View Post
Aren't these valves meant tofu ction when the engine is off? If there is water coming out of the valve the the spring I the valve probably needs replacing
Yes you're right,- the valve is designed to allow air to enter when the engine is off and thus preventing water from siphoning back into the engine cylinders; however, many don't have springs. Mine had a disc with an air hole off center that would allow air back into the system when the pressure of the running exhaust water was not pressing the disc up and sealing the hole.
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Old 31-10-2015, 21:04   #15
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Re: Anti-Siphon Loop for Raw Water Exhaust

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Originally Posted by LeaseOnLife View Post
SCOT vacuum breakers, made from Delrin, would fit the bill:
http://www.scotpumpmarine.com/sn/SN-890-913.pdf
I've had this vacuum break recommended by several sources.
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