air breaks on engine coolant

[rob2]

If I remember rightly, there are two types of syphon break used just before injection into the exhaust system. One uses a valve to allow air in when there is no pressure in the pipe, the other has just a small aperture to promote a tell-tale flow out through the breather pipe. When I stripped mine for maintenance, it was blocked with salt deposits. After soaking it clear I found a rubber diaphragm with an offset hole against a cupped seat with a central hole. Now clear, it allows a small leak of air under no flow conditions. However, if I remove the diaphragm to convert to a tell-tale, what size aperture would give a suitable flow rate? I don't want to get a hot shower everytime I start the engine!

 

[captainslarty]

lol,
on our 42 hp OM636 the break is just after the raw water pump. There is no valve at all, just a raised (above heeled water line) loop with a small take of pipe going out the port side. the size of the small take off pipe is around the size of car brake pipe, and probably IS car brake pipe !.. works well.. thats all it needs on my boat. Dont see any need to go larger at all. It does what it is supposed to do.. Normal start check is listen for water from the exhaust, dont need to look on mine, you can hear it easilly, and then a peak over the port side to see a small trickle from the vent (anti syphon) outlet.
Hope that helps..

DONT do as someone here who shall remain nameless did, and fit a half inch pipe as a vent.. he DID get a great shower as it also "vented" in the cockpit, in a vertical direction.... ooooooops.

 

[boatmike]

You can buy a skin fitting (plastic but OK as it's above WL with a hole no more than about 1/8 inch in it. Suitable pipe to fit is OK. Obviously the bigger it is the less likely to be blocked. The hole in the skin fitting will regulate flow. DONT fit it where it will pee over the legs of peeps on the pontoon when tied alongside though. They tend to object.....

 

[rob2]

Thanks, guys.
Actually, I was planning on venting into the cockpit and aiming it at the drains...
If I take the diaphragm out of the fitting, it leaves a hole of around 1mm - it sounds like that'll do!

 

[Billjratt]

Just be aware that the water can be dirty sometimes so don't let it pee black marks everywhere.