How to manufacture a butterfly valve?

Single Mono Flange Butterfly Valve 2 Piece Split Body Butterfly Valve PTFE Lined Cheap Stainless Steel Butterfly Valve EN593 Butterfly Valve Lever Type Concentric Butterfly Valve Electric Motorized Actuator Hard Seat Wafer Butterfly Valve Gear Box Butterfly Valve PTFE Seat CW Penumatic Actuator Stainless Steel Butterfly Valve Handle Lever Type Cartridge Seat Wafer Butterfly Valve Gear Operated Resilient Seat Wafer Butterfly Valve with Penumatic Actuator Wafer-style Butterfly Valve Replaceable Seat Dovetail Seat Butterfly Valve Wafer Type