vetus syphon vent for engine

[alahol2]

I'll have a go...
When the engine runs, water is drawn through the pump, through the anti-syphon loop, through the engine/heat exchanger and into the exhaust pipe at the exhaust mixer elbow, it is then 'blown' through the exhaust pipe and out of the transom fitting. If the exhaust mixer elbow is below water level, when the engine is stopped you have a situation where water can continue to syphon through the engine into the exhaust pipe. The exhaust pipe will fill with water (the transom exhaust exit is above the exhaust mixer elbow) and back up into the engine exhaust port, valves, cylinders!
The syphon break allows air into the top of the water column and prevents syphoning.
Incidentally, the syphon break is more commonly fitted between the cooling water outlet from the engine and the exhaust mixer elbow.
Also your exhaust pipe should have a water trap capable of holding all the water in the exhaust system (plus a bit for failed start attempts).
Hope that makes sense.

 

[VicS]

I'll go along with that explanation.

Equally effective in the pump outlet as in the pipe betwixt engine and exhaust injection point. Personally I think is silly throwing some of the cooling water overboard before its had a chance to cool the engine but there you go.

Vetus recommend that a syphon break be fitted if the exhaust injection point is less than 15cm above the water line. They also recommend that the device itself should be 40cm above the waterline.

Vetus offer two types. One as already mentioned with a constantly peeing discharge which can be overboard or into a cockpit drain where it is more visible ( and inclined to send the crew to the heads regularly ) The other with a valve that opens to allow air to enter when the engine is stopped. The Volvo type have a valve.

 

[LeonF]

Thanks Vic and Alahol. My device is definitely between the impeller pump and the heat exchanger. I don't think it drips water. I shall have to check and see which one it is, it's a sort of beige plastic, but an old one so nothing in the current catalogues to compare it with. I guess I might need to try and service it.

 

[LeonF]

It's the kind with a valve, not a water output. Situated high up in the cockpit locker above the calorifier. Hasn't been looked at for at least 6 years, since I bought the boat , possibly longer. Would I need spares to service it ? Thanks.

 

[Severnman]

V simple. Just ensure the spring plunger is operating correctly once you have unscrewed cap. Wash in fresh water if you find evidence of salt crystals. Annual job.

 

[VicS]

This what the Vetus ones looked like a couple of years or so ago. As far back as
1994 they looked the same but the colour has changed.

I have no idea if there are spares or an overhaul kit for them.

 

[Scomber]

hi VicS and all
any observations greatly received !
old engine - antisyphon (as shown on your above vetus information ) which i fitted a couple of seasons ago would pee water all the time (bukh20)
new beta 25-no water out at all -
i unscrewed top-no centre valve it seems clear-blew through pipe to hull exit -i tried restricting flow to new shaft seal to see if more flow would push some out-
fixing instructions do say exit pipe should fall slightly towards hull exit-i missed that so it does have a slight incline-but that never seemed to matter before !
am i missing something here ?
thanks for any advice

 

[VicS]

am i missing something here

Me too I think!