Freshwater I, II & III 1/4″ ozone check valve. Over time the ozonator check valve can begin to breakdown under the harsh conditions of ozone. The check valves have a special diaphragm (Viton) that enables them to last longer than rubber. Rubber diaphragms last about a month before the rubber becomes hard. The purpose of this check valve is to prevent water from draining out of your spa through the ozonator in the event that your spa looses power. A power loss will stop the Silentflo 5000 from operating and therefore stop the suction (Venturi effect) at the injector. Since the ozonator is installed below the surface of the water, the only thing stopping the back flow of spa water through the ozonator is this check valve. In addition to this check valve it is also recommended to loop the 1/4″ ozone tubing high (just under the spas bar top) to help keep water from constant contact with the check valve during a power failure. If your ozone bubbles have stopped bubbling up through the drain of your Hot Spring or Tiger River spa, then the check valve may have failed. A failed check valve in the closed position will prevent the ozone injector from drawing ozone from the Freshwater unit. Note: If you’re replacing the discontinued 3/16″ check valve on your Freshwater II Ozonator then you’ll need to replace the existing 3/16″ tubing from your Freshwater II to the injector with 1/4″ tubing. Installation Note: The embossed arrow on the check valve points away from the ozonator which is towards the injector.