Siphon Break question

[Irie308]

I'm trying to educate myself on how the siphon break works on the onan 9.5kw. We just returned from a 2 week trip (much of which saw the use of the gen). The siphon break is installed in the transom and i noticed that the air movement through it would get louder as the sea strainers filled with sea grass or jelly fish so I made sure i checked and cleaned them often. However I wanted to make sure the the siphon break was performing as it should. I noticed that the cap that goes over the air vent is missing. I'm inclined to just replace it. I've also read that now and then it needs to be cleaned to ensure its letting air in? I'm also not clear where the lines go. Are they on the intake side or on the exhaust side i can't really tell from the diagram. Would hate to ruin my gen by ingesting water due to a $16 part.

 

[my3sons]

The siphon break is a one-way valve that closes when it is under pressure (generator running) and opens to allow air into the raw water system between the heat exchanger and the exhaust manifold so that water won't siphon into the Generator and flood the motor when it's not running. Siphon breaks are used when a gen or other engine is installed below or within a certain distance of the waterline.
I'm not sure what you meant by air movement getting louder as the strainer filled with grass. When your gen is running the valve is closed, and if it was open, there would be water being sprayed out of it, or at least dripping.
Mine is located in the engine room, right next to the gen set. I remove the valve every spring or twice a year or so to clean it. I just swish it around in some water and blow through it to make sure it's working as it is supposed to.
A while back I noticed a little water on top of my generator starting battery and figured a piece of grit or something got under the diaphragm in the valve and it leaked a little water.
I took it off and cleaned it and no problem since. You're in a salt water environment, keep tabs on that if it leaking would be a problem where it is mounted.
Pic below shows where mine is located. Although it can't be seen in this photo, you can see the hoses and clamps that form the loop where it is located, mounted to that gray board.

 

[Irie308]

Ok, so mine is definitely leaking, not much but there is water coming out when the gen is running. Think i'll just replace as the cap seems to be missing as well

 

[my3sons]

I’m on the boat so here is a better picture. Does yours look like this?

If it does, that rubber cap on top just keeps debris out of the valve.
It’s not air tight and shouldn’t be. You could find something to put over the top of it if you want to take it off and try to clean it while you order another. Maybe keep the old one as a spare.

 

[Irie308]

Yes looks like that but nothing attached above the threads. just a white clear plastic nipple which i assume is the valve that needs to be cleaned. Will give that a shot. Thanks.

 

[PlayDate]

It should look like this:

Not sure why you have an extension on yours but given the mounting location ....the goal is to get the air vent as high in the bilge as possible.

 

[my3sons]

Yep, the extension gets it right up to the ceiling of the e/r.
I’ve known guys that have run them above deck to get them away from an area that they don’t want water dripping