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post #11 of 14 Old 09-04-2012
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Re: Vented Loop Design?

Question on the vented loop:
The vented loop on the water line to my engines water injection elbow has the vent line exiting through the hull of the boat at the stern. It has worked this way for 30 years. The vent line is somthing like 1/4 inch plastic tube. The through hull fitting has no seacock.

I am thinking of fitting a seacock but does the vented loop need to run out the hull? At some points of sail and sea state, seems the through hull could be under water.
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post #12 of 14 Old 09-04-2012
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Re: Vented Loop Design?

Quote:
Originally Posted by Maine Sail View Post
Just be sure your "exit" hose does not have any dips in it that can collect and hold water. With a bad impeller even a small "trap" can cause a siphon.

For engine vacuum breakers I prefer the ones made by the Scot Pump Co. as I find they are far more trouble free than a duck bill....

You can buy just the vacuum breaker:

Or the whole thing:

I tend to just make custom ones:



This was Ericson's idea for a siphon break and it sprayed salt water all over the engine when the brazed copper tube failed. It was also mounted under the cockpit:


A few dollars and 30 minutes later a new one that is significantly more robust replaced it.
Main Sail,
In the last (bottom pic) where does the vent hose go?
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post #13 of 14 Old 09-04-2012
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Re: Vented Loop Design?

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Originally Posted by casey1999 View Post
Main Sail,
In the last (bottom pic) where does the vent hose go?

Out the transom. Gives a nice "tell tale" spit....

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post #14 of 14 Old 09-04-2012
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Re: Vented Loop Design?

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Originally Posted by bvander66 View Post
Dont recommend marelon vented loops in the exhaust water, should be metal. Exception is Vetus makes an exhaust quality plastic/grp one.

Vented loops/siphon breaks/vacuum breakers are inserted into the raw water intake side of the system not generally into the "exhaust" system.. The water is still cool before it enters the RW exhaust injection elbow. There are literally thousands upon thousands of vessels out there with Marelon siphon breaks to protect the RW circuit from a siphoning event. While I am not a huge fan of the "duck bill", and generally prefer the Scot break, they work fine for an engine siphon break and are specifically sold for that as one of the intended uses...

Beyond that Marelon is the only plastic I know of to pass the stringent USCG fuel valve burn test. A Marelon valve sustained temps to 1275 degrees with the majority of the burn test time being between 850f & 980F. The valve did not leak any gasoline and passed the tests. If you hit anywhere close to these temps in a wet exhaust system, especially on the RW injection side, you have much bigger problems to worry about..

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Last edited by Maine Sail; 09-04-2012 at 07:24 PM.
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