Volvo vacuum valve

[Quandary]

I suspect this may have come up before, if so apologies.
My nearly new Volvo D1-30 has a 'vacuum valve' mounted above it, an inverted loop of open narrow tube, which likes to drip cooling water over the engine from time to time. The valve has been dismantled and it and the little rubber diaphragm is clean. But it still spits and while the quantity is small, I don't like the idea of sea water showering down on top of the electrics etc.
I had a similar problem on a 2003 which I eventually dealt with by putting in a piece of very loose fitting stiff tube leading into a plastic bottle, I collected less than 1/2 litre per year.
I am tempted to do the same again, any reason why not?
What is the purpose of this gadget, is it to stop water sucking back from the exhaust in some circumstance and why does it drip when clean, the manual is a bit vague (though it advises that it must be kept clear of salt and dirt), the exhaust loops up high under the transom and across the stern and discharges well above water level though the outlet possibly could be immersed if motor sailing to windward but I am unlikely to be doing this when there is enough wind to heel the boat this much.

 

[Bilgediver]

It is a vacuum breaker and when you stop the engine it breaks the syphon in the adjacent loop

So long as the container is mounted adjacent to the valve , is open topped and the tube goes to the top of the container it will work.

Long tubes to low level must be avoided as they defeat the purpose of the loop especially if dipping into liquid.

 

[mustntgrumble]

This is an insignificant but vital bit of kit - the little rubber job really does need to be kept clean of salt crystals to ensure it breaks the siphon when engine is off so coolant seawater doesn't run into the exhaust & back up into the engine via open exhaust valves.

I learnt about this the hard way - the job was on my "to do" list but was put off in the rush for the first sail of 2009..... the replacement engine is going in this week.

Anyone interested in ancillary bits off a lightly used Volvo 2003T? All in g.w.o. except for damp innards

 

[VicS]

It's an antisyphon valve. If the cooling water injection point into the exhaust is not above the waterline then when not running water can flow slowly through the system filling the exhaust and eventually flooding into the engine.

Problem solved by taking the pipework into a loop well above the w/l and fitting a device at the top of the loop that will open and allow air to enter to break the syphon.

Normal I think for the Volvo ones to leak!

Maybe a Vetus one would do better. Alternatively Vetus do a version without the troublesome valve but with a small vent pipe that discharges continuously overboard or into a cockpit drain while the engine is running.

 

[Quandary]

Thanks so far, if it leaks water I presume it also works in breaking the vacuum, am I right?
The ID of the extension tube to the bottle will be about twice the OD of the valve outlet in order to break the seal at the discharge point so even if the bottle fills it will not seal.
These valves seem very simple but are they generally reliable or is mine typical?
Is there still a risk if the exhaust pipe is open and discharges above the water.

 

[mustntgrumble]

After recent expensive experience I won't rely on it again - I'm going for the vent that continuously piddles into a cockpit drain, then I can see the system working.

I'm told the open exhaust pipe should be ok as long as you have a loop in the pipe that goes well above the worst case waterline, tho can't say I like the look of it much

 

[VicS]

[ QUOTE ]
Is there still a risk if the exhaust pipe is open and discharges above the water

[/ QUOTE ] Yes probably.
Normally the exhaust rises before discharge and would trap water piddling into it.
Some useful info in the Vetus catalogue on pages 168 and 177 with all the bits and pieces on the pages in between.

 

[Quandary]

Vic, Thank you for the info.
Am I right in concluding that a leaking valve is safe if inconvenient, my last boat had this problem for many years and other than emptying the container occasionally I had no problems but then I did not have this forum to enlighten me then..