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Old 09-03-2016, 14:51   #1
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Alternative to rubber siphon break valve

I thought I would pass this along.

Our Forspar vent loop was not functioning properly with respect to breaking the siphon. It was not clogged and appeared to be physically ok. On inspection, the small rubber duckbill component just did not seem to be up to the task of being our antisiphon component for our head intake loop.

I removed the cap and the rubber bit and replaced it with a 1 inch long piece of 1/2 inch dia rubber hose and a hose clamp. On the open end of the section of hose, I inserted a 1/2 whale check valve. If you cut off the non-valve part of the check valve, it fits neatly into the hose.

Seem to work quite well so far. No leaks on flushing and no siphoning from the raw water intake hose.

Comments?
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Old 09-03-2016, 16:58   #2
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Re: Alternative to rubber siphon break valve

The little diaphragm in a siphon break (vented loop) air valve does wear out or become degraded by salt and sea water minerals, requiring replacement of the valve. If the valve isn't clogged or crusted, you're not likely to notice the pinhole(s) or miniscule tears in the diaphragm. The warmer the water, the higher the salt and mineral content, so periodic cleaning will help to extend the life of the rubber diaphragm. But eventually everything wears out and air valves aren't expensive.

Because air valves are typically sold separately from loops, a lot of boat owners don't even know they exist...the only solution they can think of that will put an end to water or waste squirting out the hole in the nipple on the top of the loop is to put a vent line on it.

BAD IDEA because the tube has to be so small--only 1/4" inner diameter--that it very quickly becomes clogged at the connection with salt and sea water minerals, turning the vented loop into an UNvented loop that no longer has any ability to break a siphon. Because the vent line has solved the pesky squirting problem, it's out of sight, out of mind, so it's never cleaned.
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Old 10-03-2016, 08:38   #3
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Re: Alternative to rubber siphon break valve

Hello Peggy:



Thanks for the input.



In the case of the whale valve, the line is 1/2 inch inner diameter versus something smaller say 1/4 inch, so the chances of the valve getting clogged are much less than the original Forspar design. The use of a vent line versus an anti-siphon valve would not be as elegant in this application.

The original Forspar design even when new and clean was not allowing enough air in to break the siphon. The 1/2 inch valve allows the loop to function as designed.


I have a vent line versus an anti-siphon valve on my main engine and generator, where they work great, but those are in enclosed spaces. The vent loop with the whale valve on the head intake line looks unobtrusive and can be visually detected in case it starts to malfunction.
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