The Type 57 Butterfly Valve incorporates four major design upgrades in thermoplastic valve technology. New design features include a flange stopper, which prevents the valve liner from over compression. A second feature is a molded body absorption channel. These two design innovations work together to eliminate seat compression from effective stem torque, resulting in higher cycle life. A spherical disc provides increased flow characteristics and is less intrusive to piping systems. Also, the Type 57 is produced with the first all-plastic gear operator: Plasgear.