Abstract: A driving device for opening and closing a valve comprises a cylindrical body, an actuating cylinder, a spindle, a piston member, a transparent plate and a stop means for controlling the rotation of the spindle. Said stop means comprises a ring gear, a spring and a stop bar having a wedge-shaped head, said wedge head having a pair of surfaces forming an included angle which is bisected by the axis of the stop bar such that rotation of the spindle by fluid pressure on the valve is prevented but manual rotation of the spindle in either direction is permitted.

Abstract: A butterfly valve comprises a valve body, a valve seat, a valve stem, a valve member and sealing assemblies. The valve seat has three layers such as a first, a second and a third layers which are formed from hard synthetic resin, resilient material and fluororesin respectively. An effective seal can be achieved by providing an inwardly convex contour on the inner peripheral surface of the valve seat.

Abstract: A butterfly valve comprises a valve body, a valve seat, a valve stem, a valve member and sealing assemblies in which the central portion of a seat face of the valve seat is raised higher than both of its side portions and the diameter of the valve seat at the central raised portion is smaller than that of the valve member whereby a perfect seal can be achieved.