Gravity flow system valve The Schenck Process manually and air-operated 2-way �A� Valves are used in gravity flow systems and come equipped with square, flanged inlet and outlet ports. The �A� Valve is designed to divert product flow from one source into two destinations. The angle of both legs is 30° off vertical centerline. The �A� Valve is available with either a urethane flapper with shaft, bearings and bearing seal or a white, food grade neoprene flapper secured by a metal blade