The 1" vented loop acts as an anti siphon valve for engine cooling systems. Installed in the raw water circuit between the exit from the heat exchanger and the inlet to the exhaust riser.
Its purpose is to introduce air at the high point of the raw water cooling circuit when the engine is shut down. This breaks any siphon that might cause sea water to flow into an open engine exhaust port, into the cylinder, and ruin the engine.
1) An anti siphon valve introduces a small amount of air into the hose whenever a small suction is detected. This breaks the siphon and prevents flooding your boat. There is a tiny rubber "duck bill" valve that is critical to its proper function. If the rubber gets old and stiff it may not function properly putting your boat at risk. Test your anti siphon valves yearly to ensure that they are working properly.
• Plug one end of the "U" and blow into the other side. No air should exit the top of the "U" at the duck bill fitting.
• With one end still plugged, suck on the other end and air should enter the "U" through the duck bill fitting at the top of the "U".
If either of the above tests fail, you should replace your anti siphon valve as it is not functioning properly and can result in a flooded engine or boat.
Order the replacement part below under "May we also suggest".
2) Always measure the i.d. of the hose before ordering. Although we believe the boat categories this part is listed are accurate, there is no guarantee that your boat was built exactly as expected.