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When to Use an Anti-Siphon Exhaust

If the mid-line of the unit is to be installed at or below the waterline of the vessel, a Siphon Break must be used. Either a "valve" or "tee" type can be used.

Siphon Break Valve
The valve must always be at least 10" above the waterline, regardless of the pitch and roll of the vessel. There is no maximum height. Commercially available anti-siphon valves are fairly reliable; however, they do get fouled and can stick in either the open or closed position. Regular maintenance is necessary.

Siphon Break Tee
The "tee" method is a more reliable type of siphon break. The tee is generally designed with 1/2" hose barbs on the input and output connections and a smaller connection on the branch. The branch hole should be restricted to 1/8" dia. Mount the tee a minimum of 10" above the vessel's waterline. The branch side of the tee is connected to an overboard thru hull, also mounted above the waterline. Or, the branch side of the tee can be tapped into the exhaust hose, after the Silencers. The hose from the branch should always flow in a continuous up or down direction. Never loop the hose up and down. If in doubt, call us for consultation. The thru hull should be mounted so it is always vented to atmosphere, never under water.


Connections for Anti-Siphon System

Remove the hose (16/12) that connects the Heat Exchanger to the Exhaust Elbow Inlet. Install a new 1/2" wire reinforced hose between the Heat Exchanger and the inlet of the anti-siphon device. Install a second 1/2" wire reinforced hose between the outlet of the siphon break and the exhaust water Inlet on the Exhaust Elbow.

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