Anti-syphon valve in engine cooling loop

[dougln]

I have to replace the anti-syphon valve on the raw water cooling loop for my Volvo 2002. I have been looking for suitable devices and have found that Vetus do a couple of alternatives - a type V and a type H. The type H comes with a skin fitting and hose to enable the 'breather' port to be connected out through the hull, whereas the type V is what I consider the normal type with a simple open breather port.

Can someone explain why I would need to vent through the hull? I thought that this valve just provided a suction break and therefore the breather port allowed air in and a check valve prevented water being vented through the same.

Any clarification would be appreciated. Are there any alternatives to Vetus that anyone could recommend?

Finally, does anyone know of a suitable flow meter (with remote display) that I can put in the cooling water loop to provide positive indication that the impellor is working.

Thanks in advance.

 

[Ships_Cat]

The anti siphon valves (the ones that relieve air but close when water is present) have a tendency to leak. In my experience leakage is most likely to occur if they are exposed to the exhaust pulsations back through the raw water from the point where it is injected into the exhaust (putting aside poor maintenance).

A common way around this is to do away with the valve itself in the antisiphon fitting and just run a drain from this overboard so that when the engine is running water is continually pumped out through it. That is the alternative that you refer to.

On our own boat we have 2 loops on the engine, both with valves - one in the main raw water system and another in the take off downstream of the raw water pump that supplies water to the stern gland. The one in the main raw water system is never a problem but the one for the gland take off occasionally is - it is more exposed to the exhaust pulsations back through the raw water.

Some types (not, I think, Vetus though) use a small rubber ducksbill valve (eg Forespar) leakage of this type can usually be stopped by a very thin smear of petroleum jelly on the sealing surfaces of the ducksbill (but not enough to gum it up). Whatever, it is a good idea in my opinion to install the antisiphon valves in a position where leakage will be direct into the bilge or somewhere where it can be seen if it occurs and without harming other equipment.

John

 

[jfkal]

Unless you maintain it well it will start to leak and if stuck open (salt deposits) you spray your engine with salt water. Not a good idea. You can vent it anywhere in the boat where it does no harm. But the common way is to give it its own small through hull.

 

[dougln]

Thanks for the replies. Any idea of a water flow rate so that I can try and source a flow meter?

 

[hairbox]

Hi all How do you service anti siphon valves is it a case of just removing and rinsing out with fresh water ?
cheers all

 

[philip_stevens]

If it is the type with the valve in it, and not venting overside, yes, just remove it and wash it in warm soapy water to remove any salt deposits. The salt deposits are what others have referred to when getting a small leak.

The overside type is better as it allows you to see that water is pumping through the engine.

There are many low flow switches available, but have a look here for a start http://rswww.com/cgi-bin/bv/rswww/subRangeAction.do?cacheID=uknetscape

 

[VicS]

Can also be vented so that the water goes into a cockpit drain. More visible than overboard but not every one will be happy with a constant flow of water in sight.

 

[boatmike]

Hi John,
hope you enjoyed your nice warm Christmas.
I have a thing about these little monsters and now avoid the ones with any form of valve in completely. I agree they can leak, and do, but this is a minor problem and only means a little bit of water in the bilge. More dangerous entirely is that they can seize up closed and not work. This is particularly prevalent if the boat is laid up over winter. If they don't work and the water then syphons back when the engine stops, which is what they are designed to prevent, the result can be a catastrophic engine failure. So why fit a valve at all? The obvious solution is a small pipe to a little skin fitting adjacent to the main exhaust outlet. When the engine is running you can easily see the water flowing showing it ain't blocked and it can't fail.. The stupid valves not only can fail but do fail, and when they fail shut its disasterous. No contest then in my book. NEVER fit the ones with valves in as it introduces an unnecessary risk of possibly very serious failure. There are enough things to go wrong on a boat without introducing more, especially when it's so easily avoidable. As a bonus, with the valveless sort you will NEVER get leaks into your bilges....

 

[snowleopard]

The big danger with the valve type is that it can get clogged with salt crystals and no longer admit air so you get a syphon, fill the exhaust and break your engine with a hydraulic lock. They must be dismantled and rinsed out at least once a year.

The free-flow type with through-hull don't clog and give a constant indication that the cooling water is flowing. Some people fit them so they flow into the cockpit drains so you can always see the flow. The down side is that a constant flow can cause staining of topsides or whatever.

 

[Ships_Cat]

Hi Mike

Yes, Christmas in the warm was very nice thanks. Even better after seeing all the snowy photos others have posted /forums/images/graemlins/smile.gif.

I agree with your valve comments, especially the jambing closed case. The rubber duck bill ones are, I think, more reliable in that regard and have not personally had a problem with them not venting on our own boat. Reason they were used is that a problem that can occur when using a valveless arrangement is when the engine is surrounded by open space accomodation, as then it can be awkward (but not impossible) running the vent to the topsides or transom in such a way that it will drain down properly to vent the loop when the engine is stopped.

Perhaps another case for catamarans, as they usually have topsides both sides of the engine compartment /forums/images/graemlins/smile.gif.

John

 

[philip_stevens]

/forums/images/graemlins/blush.gif Sorry my link didn't work, but if you go to http://rswww.com and type in "flow switch" in the search box, quite a few are found.