The siphon breaker plays a crucial role in a marine exhaust system, preventing the cooling water backing up into the engine when this is low in the hull. The Halyard unit is cast from bronze, and incorporates a tapping point for some cooling water to be drawn off to feed the stern tube bearings

The 'U' bend on the top of the unit will emit water very occasionally, and this can be drained into the bilge or overboard. It must not be drained into an enclosed container due to the risk of water siphoning back.
 

Items shown with shaded background are stock sizes

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