The Watts PB34 3/4" PumpBuddy Plastic Dual Level Tank Valve is an outlet control device that allows variable minimum and maximum water level settings within a water tank when filling from a pump. For rainwater harvesting applications, it works as a backup water supply control valve, in the event demand exceeds rainfall. It has a large flow rate. It utilizes a differential dual weight system that reduces pump wear and saves electricity. This valve is diaphragm activated and has a steel pin that runs inside the pilot center which acts as a self cleaning mechanism which is unique to Apex valves.