Actuating apparatus for adjusting a movable element, particularly the

Abstract

The invention relates to a valve assembly. A closure member for the valve unit is controlled directly or indirectly by a movable wall of an expansible chamber filled with a refrigerant medium having vapor and liquid phases. The pressure exerted by the vapor phase of the medium provides a bias which is directly related to the temperature of the liquid phase. A heat transfer element such as a heating resistor in the liquid phase is heated or allowed to cool in a controlled manner by an external control unit. A temperature responsive sensor element in the liquid phase of the medium is part of a feedback system for the control unit which allows a selected temperature to be maintained in the chamber which results in a desired constant pressure to be maintained in the chamber. A pilot valve unit is disposed between the valve closure member and the movable wall. An expansible chamber behind the closure member houses a spring for biasing in a valve closing direction. A bypass throttle passage has a first section extending from the valve inlet to the expansible chamber and a second section extending from the expansible chamber to the valve outlet. The pilot valve unit includes a valve element operably connected to the movable wall for controlling fluid flow through the second bypass section and thus control the opening of the valve closure element.