Abstract: A control system for a valve actuator which is subject to oppositely directed displacement due to thermal expansion and spring forces has sensor switches which detect successively greater amounts of compression of a spring which compresses to accommodate thermal expansion of the valve, its stem and seat when the valve is seated in closed position. A position servomechanism which is responsive to the position of the stem and a control signal operates a motor for advancing and retracting the stem.

Abstract: Disclosed is a slide valve in which the valve internals, the valve seat, guides and slide valve are maintained in position by a clamping action of an abutment in the valve body and on the valve liner secured in the body by a quick make-up connection. The slide valve is suited for all sizes of valves, both large and small and no screws or other fasteners are needed to maintain the valve internals in position. Advantageously, the guides and slides of the slide valve are maintained out of the flow path, and the valve internals including the orifice assembly with its valve seat and guides, and slide valve with its slides are readily removable through the bonnet area.