Abstract: A butterfly valve includes a valve housing having a fluid conduit, a seal plate assembly including a seal plate, and a closure assembly. The closure assembly includes a main shaft mounted in the valve housing and rotatable about a longitudinal axis between an open position and an intermediate position, a crank shaft rotatable about the longitudinal axis between the open position and a closed position, a hub affixed to the main shaft and movably coupled to the seal plate assembly to permit translation of the seal plate assembly with respect to the hub, a roller engaging the seal plate assembly and mounted to the crank shaft for eccentric rotation about the longitudinal axis, and one or more springs coupled between the seal plate assembly and the hub for biasing the seal plate toward the intermediate position. The valve may include a valve actuator which rotates the crank shaft about the longitudinal axis between the open position and the closed position.