GB677097A - Improvements in control gear for steam turbines - Google Patents

Abstract

677,097. Fluid-pressure servomotor-control systems. ENGLISH ELECTRIC CO., Ltd. Jan. 19, 1951 [Feb. 10, 1950], No. 3462/50. Class 135. In a speed control for a steam turbine, the movements of the speed governor sleeve are transmitted mechanically to a piston valve working in a movable, ported, follow-up sleeve to control the leakoff from a chamber which is connected with the ported sleeve and is supplied with pressure liquid, the chamber also communicating hydraulically with a power device actuating the main steam valves of the turbine, and the ported sleeve, which moves through the chamber wall, is provided with a flange connected to the chamber by a bellows so that the control pressure in the chamber can act on the flange in opposition to a resilient restoring force. The centrifugal governor 1 acts through a bell crank 3 and an adjustable link 6 on a lever 5 pivoted on a normally-fixed fulcrum 36, and the lever moves a piston valve 15 to vary the area of escape ports 16 for pressure fluid supplied to a cylinder 17 from a line 50, past a restriction 20. The ports 16 are provided in a movable sleeve 19 which has a bellows seal 29 with the cylinder and which is pressed upwards by an adjustable spring 18 ; and the modulated pressure produced in the cylinder by movement of valve 15 acts on a piston flange 39 on the sleeve 19 to neutralise the movement of the valve and so provide a follow-up pressure in the cylinder. This pressure is communicated to pistons 23, 123 which, through floating levers 24, 124, actuate valves 30, 130 controlling servomotors 25, 125 connected to the inlet valves 28, 128 of the turbines. The movements of the servomotor pistons are fed back to the valves 30, 130 through the floating levers 24, 124 so as to provide a further follow-up. The fulcrum 36 of lever 5 is carried on a piston 69 which is normally pressed upwards, against its spring loading, by an oil pressure produced by a control apparatus subject to the vacuum in a turbine. Should the vacuum fail, this oil pressure will fall and piston 69 will move lever 5 to a position such that the inlet valves of the turbines are shut down. There is a screw-and-nut connection between lever 5 and the stem of valve 15 so that the position of the valve can be adjusted to set the control speed of the governor by means of a hand-wheel 13 or a remotely-controlled motor 11.