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Old 08-07-2011, 12:07   #1
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Onan (?) Anti-Syphon Valve

I have an Onan generotor and there is an anti-syphon loop + valve. I ought to clean the valve. Any tips on this. Do I remove the whole thing from the two pipes and simply dismantle? I am a bit confused by the yellow widget

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TS

Here's a photo.
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Old 08-07-2011, 12:21   #2
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Re: Onan (?) anti-syphon valve

It looks odd to me. Can you actually see the siphon hole? I had a marine mechanic tell me that when they begin to fail they leak a bit and people often plug them in one way or another not understanding the function. If you have any doubt about it I'd replace the valve. It can really "suck" when they fail The wierd thing is they can be non-functional for years and then one day all the conditions are just right and you have water in the cylinders.
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Old 08-07-2011, 14:50   #3
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Re: Onan (?) anti-syphon valve

It looks like someone put a heat shrink "sock" over the siphon break/breather valve, totally disabling it. Not good, especially if the genny engine is below the waterline.

See also ➥ Waterline vs Raw-Water Strainer

And ➥ http://www.northern-lights.com/PDFs/...t_drown_me.pdf
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Old 08-07-2011, 15:08   #4
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Onan anti-syphon valve aka siphon break

Quote:
Originally Posted by GordMay View Post
It looks like someone put a heat shrink "sock" over the siphon break/breather valve, totally disabling it. Not good, especially if the genny engine is below the waterline.

See also ➥ Waterline vs Raw-Water Strainer

And ➥ http://www.northern-lights.com/PDFs/...t_drown_me.pdf
I have done some further research and found that this is how Onan shows it in their brochure here at page 36 and they call it a siphon break..
I think that what I am now missing is the "Instruction sheet G-567"

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Old 11-07-2011, 14:14   #5
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Re: Onan (?) Anti-Syphon Valve

take it off and flush it with a hose and see if the anti siphon valve actually works. Should provide an air break when water flow shuts off to break a siphon, but not leak when water pressure is in the tube.
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Old 11-07-2011, 14:52   #6
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Re: Onan (?) Anti-Syphon Valve

I also have Onan gensets, and you got me looking at the manuals because I have no siphon breaker installed on them. The installation book for the MDKAD 21.5KW unit calls for a siphon breaker IF the "exhaust manifold injection-port is at or below the load-waterline". Mine is about 18" above it.

It is interesting that they do not specify any particular type of siphon breaker, and none is listed in the Onan parts catalog.
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Old 11-07-2011, 16:53   #7
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Re: Onan (?) Anti-Syphon Valve

Make your life easier and run a nice 1/4"-1/2" hose straight from the top of that loop to a skin fitting in the cockpit or topsides. Any more or less vertical surface will do. I have had a little spring and piston valve fail and 10 kerosene flushes of the diesel later, I swore "never again". A straight hose length can be screened, removed and cleaned with water. A little spring fails or piston sticks and your genset is trying to burn cooling water.

Bah.
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