How to stop siphoning?

[cmedsailor]

I have this “fear” that my engine’s vented loop valve may get stuck leading to siphon backflow with all resulting negative results. Yes, I do clean it every year with fresh water, it’s a good quality product (vetus) and my boat has a muffler. Small possibility of failure but you never know!
Anyway, the best method of course to stop siphoning, thus avoiding any siphon backflow is to simply close the engine seacock when the engine is off and keep it closed.
What if I close the seacock for a few seconds and then open it so I don’t need to go up and down the cockpit twice (or forget it closed and start the engine)? Sea water flow will stop but what about the pressure? Probably an easy question for anybody with basic knowledge of physics but not for me!!
Thanks

 

[noelex]

If you have a clear hose you can confirm the water has drained out when the engine stops. The other option is to do away with valve and have a "piddling" tube, this is less likely to clog and you can confirm water is getting out.
The more common cause of water in an engine is poor instalation or internally corroded exhaust elbow.

 

[trapezeartist]

It really is safest to close the seacock when the boat is unattended. To ensure you don't attempt to start the engine with it closed, hang the starter key on the handle of the seacock.

 

[pvb]

I have this “fear” that my engine’s vented loop valve may get stuck leading to siphon backflow with all resulting negative results. Yes, I do clean it every year with fresh water, it’s a good quality product (vetus) and my boat has a muffler. Small possibility of failure but you never know!

I reckon your fear is irrational and unnecessary. But, if you're that worried, why not simply install a second vented loop in series with the existing one? And maybe a third vented loop as well?

 

[cmedsailor]

I reckon your fear is irrational and unnecessary. But, if you're that worried, why not simply install a second vented loop in series with the existing one? And maybe a third vented loop as well?

Irrational and unnecessary? Most probably yes you are right. I feel quite comfortable with the wind and the sails (I have been windsurfing for more than 20 years) but when it comes to engine matters, that's my really weak point. Probably worry too much.
However, I didn't know that you could add more than one vented loop and that's a very easy thing to do.

 

[kieronriley]

Sea cock

I have a sea cock fitted to my exhaust on a petter mini twin for the same reason as you describe,I did once forget to open it and tried to start the engine,it simply would not start despite a few attempts then my brain woke,I opened the sea cock and the engine started ok.that was about two years ago so I must not have caused any damage.Kieron