NOVELTY -. The valve for use in a central heating system has an inlet [Z] and outlet [A]. Screwed into the valve body is a plug [VK] that has a turbine [T] which rotates at a speed proportional to the flow rate. The output spindle is coupled to a generator [GE] and this provides an input to a controller [St]. The controller applies an input to a throttle [SG] to regulate the flow. ADVANTAGE - Provides accurate control of flow.