Exhaust anti siphon

Don S/V ILLusion · Jan 22, 2012

It may not be essential but it is a good idea. I wouldn't use the plastic valve though; Vetus et.al. make brass valves which won't deteriorate with heat and are arguably easier to clean.

Maine Sail · Jan 22, 2012

CYQK said:
Ready to install a new exhaust and raw water tubes. The PO never installed an anti syphon valve on the raw water intake or the exhaust hose aft to the exit fitting.
The engine appears to be at least ,or more than one foot above the water line

Still need an anti-syphon valve on the intake?

Looking at some of the Vetus exhaust fittings right now the exhaust hose just is routed over a structural beam and llooped back down to the exit

Worth it to buy the Vetus plastic stacks to loop the exhaust hose? Need anti-syphon on the exhaust?
Thanks
Gary

It is always a good idea to have a siphon break on a wet exhaust sailboat. The siphon break does not go on the "intake" it installed on the "pressure side" between the heat exchanger RW outlet and the and the exhaust water injection elbow. Try to keep it as high as you can and as close to the center-line as possible. As long as there is a good "high loop" in the exhaust hose leaving the water lift muffler there is less need there for a siphon break in that hose.

I have found the siphon breaks from the Scot Pump Company to be among the most reliable and trouble free of any I have used or worked on.

mitiempo · Jan 22, 2012

Here is a diagram from Yanmar that makes it easy to understand.

Don12364 · Jan 22, 2012

As previous posters have hinted, the valves on anti siphons are not without their troubles. They either seal up or leak. Mostly they need attention at least once a year.

Being a Beneteau, presumably your boat was built professionally and I doubt if a previous owner would have removed the anti-siphon if there was one installed by the builders.
So; if you can confirm the injection point for raw cooling water into the exhaust is, as you suspect, more than, say, 10 inches above water level, and no previous owner has suffered from water filling the exhaust and feeding back through the exhaust manifold and into the engine - then I would be strongly tempted to leave well alone.

mitiempo · Jan 22, 2012

You don't need a valve. Often a small hose is connected to the top of the anti siphon and exits in the cockpit footwell (over a drain) as a telltale that water is flowing. Alternatively it could exit the transom.

WayneH · Jan 22, 2012

mitiempo said:
You don't need a valve. Often a small hose is connected to the top of the anti siphon and exits in the cockpit footwell (over a drain) as a telltale that water is flowing. Alternatively it could exit the transom.

OK OK I'm having a stupid moment here. I've got the little hose but on my boat it goes into the bilge which I hate. (Something else to fix, later) But if you want to know if water is flowing, why not just look out the back at the exhaust. Any water you have in the exhaust has to go out the tailpipe.

So why do I need to see water from the vacuum breaker?

mitiempo · Jan 22, 2012

You don't need to see it. But if you want an anti siphon break on the raw water inlet on the exhaust elbow, and don't want to ever deal with a clogged valve, it is a good solution. It is also not as easy to see the exhaust on some boats where it exits under the counter.

FastOlson · Jan 22, 2012

mitiempo said:
You don't need a valve. Often a small hose is connected to the top of the anti siphon and exits in the cockpit footwell (over a drain) as a telltale that water is flowing. Alternatively it could exit the transom.

The small thruhull on the transom is normal for Universal diesel installations on a ton of boats in the 80's. Ours has one -- it "pees" a little stream all the time the engine is running.

L

Stu Jackson · Jan 23, 2012

http://www.goodoldboat.com/reader_services/articles/Marine_exhaust.php

Exhaust anti siphon

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