Patent GB-525724-A (GB)
Title: Improvements in fluid-pressure servomotor systems for governing prime movers
IPC: G05D13/00
Filed: 1939-02-27
Abstract: 525,724. Fluid-pressure servomotor systems. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Feb. 27, 1939, No, 6411. Convention date, March 2, 1938. [Class 135] Fig. 3 shows a servomotor for adjusting the admission valve of a turbine in accordance with the speed, the valve being connected by a lever 19 to the servomotor piston 66 controlled by a relay valve 53 in accordance with a secondary pressure supplied by a pipe 44 to bellows 48, 48a, this pressure being maintained at a constant ratio to a primary.pressure which is proportional to the speed of the turbine, since it is supplied by the impeller 13 of the turbine rotor. The primary pressure is conveyed by a passage 15 to a bellows 23 connected to an abutment plate 25, which is acted on by an adjustable spring 26 and bears against the end 35 of a valve 38, 39. This valve is formed with an annular space 42 in which the secondary pressure is maintained at the desired ratio by the action of the valve in controlling admission of pressure to the space through a passage 40a and port 40, or exhaust therefrom through a port 41. To avoid static friction in the valve 38, 39, it is rotated by a turbine wheel 37. The secondary pressure built up in the space 42 then acts through the pipe 44 against an abutment plate 49 on the bellows 48, so as to adjust a valve 50, against the lower end of which the relay valve 53 is maintained by a spring 79. Pressure from the impeller 13 also acts, through an orifice 52 and chamber 51, upon the top of the relay valve 53, tending to press it away from the valve 50, so that the fluid can leak away through the bore 53a. The valve 53 thus follows up the valve 50 according as it is moved by the secondary pressure, and the piston 66 is thus operated to adjust the admission valve. A follow-up movement is imparted to the valve 50 from the piston 66 through a lever 68 pivoted.at 69 and connected to the spring 72. In the case of a bleeder turbine, the bleeder pressure may be supplied by a passage 81 to the bellows 48a. Fig. 6 indicates means for modifying the action of the servomotor, wherein accumulators 89, 99 are selectively brought into communication with the spaces 85, 42, 86 of the valve 38, 39, so as to delay the action of the pressure in these spaces. The connection or cutting-out of these accumulators is effected by means of adjustable valves 88, 91, 93, 95, 97 and 101 arranged in the system of passages shown. For standard or ordinary operation of the servomotor, both accumulators are cut out of action. For anticipating operation, i.e. for obtaining adjustment of the admission valve in advance of an expected large change of load, the accumulator 89 is connected to the space 85. For sluggish operation, the accumulator 89 is brought into communication with the supply pipe 44 and the space 42. For isochronous operation, maintaining the turbine speed constant for all loads, the accumulator 89 is cut out, and the accumulator 99 is connected to both chambers 85 and 86 by opening the valves 97 and 101. The degree of isochronous operation may be varied by connecting the chamber 86 more or less to a drain passage 100 through the valve 101. A hand adjustment of the spring 26 is provided for effecting changes of speed.