Patent GB-638162-A (GB)
Title: Improvements in and relating to governing systems for prime movers
IPC: F01D17/26
Filed: 1947-04-21
Abstract: 638,162. Fluid-pressure servomotor-control systems. BRITISH THOMSON-HOUSTON CO., Ltd. April 21, 1947, No. 10593. Convention date, April 23, 1946. [Class 135] [Also in Group XXVI] A governing system for a prime mover, such as a steam turbine driving a generator 2 feeding a network 4 in parallel with similar turbo-generators comprises an inlet valve 7 for admitting driving fluid to the prime mover actuated by a power piston 11 under the control of a pilot valve 17 actuated by a governor 16 responsive to the speed of the prime mover, adjustable stop means for limiting the movement of the valve 7 in the opening direction to a preselected value and under-speed release means for rendering the adjustable stop means ineffective and restoring control of the valve 7 to the governor-operated valve 17 when the speed decreases to a predetermined value. Further adjustable stop means are also provided for limiting the lift of the main valve 7 to a second preselected value greater than the first and such means are automatically moved to the " no load " or valve-closed position when the speed exceeds a predetermined value. The valve 17 has lands 18, 19 controlling supply and drain ports 23, 26 in a moving sleeve 20 connected by a linkage 31, 34, 34a to the power piston 11. The sleeve 20 has a yoke 30 on which the floating lever 31 is pivoted. The lever 31 and hence the governed speed is adjusted by a screw 36 either manually or from a remote point by a synchronizing motor. The pilot valve is supplied through a passage 27 and the power cylinder 12 through a conduit 29. The spring-loaded power piston 11 carries a ported tubular extension co-operating with a second pilot valve 47 having lands 48, 49. Upward movement of the piston 11 under the control of the valve 17 is stopped when ports 46 are closed by the land 49 so that the passage 27 is cut off from a fluid pressure supply conduit 45. The pilot valve 47 is carried by a rod 53 having a stop member 52 held against one arm 51 of a bell-crank 51, 56 by a spring 55 abutting a flange 54. The position of the bell-crank and hence. the maximum opening movement of the valve 7 may be adjusted by a screw 57 operated by a hand wheel 60 having a bushing 59 splined to the screw 57. The screw 57 operates in a nut 62 urged to the right by a spring 68 and held in position by a latch 65 engaging a linkage 63, 64 connected to the nut. The latch is released by a spring pressed trip rod 66 when the latter is freed by a latch lever 73 operated by an emergency over-speed governor 72. The bell-crank arm 51 then moves to the " no load " position shown by the dot-dash line 70 and a collar 69 on the screw 57 engages a support housing 58. The latch 65 is re-set by the hand wheel 60, the nut 62 engaging a camshaped end 67 on the latch 65, The " full load " position of the arm 51 is shown by the dot-dash line 71. A secondary load limit between the " no load " position and the upper limit set by the screw 57 is set by a further bell-crank 78, 79 operated by a screw 80 having a nut 89 with latching mechanism 90, 91, 92 similar to that of the screw 57. The screw 80 is adjustable by a hand wheel 84 at the turbine or remotely by a motor 85 and gearing 87. A spring-pressed friction disc 86 enables the hand wheel 84 to be operated when the gear 87 is stationary. A collar 100 limits the movement of the screw 80 under a spring 99 when the latch 92 is released. The latch lever 92 is released when the speed falls below the predetermined value by a servomotor 95 acting against a spring 93a and controlled by a third pilot valve 103 unitary with the first pilot valve 17. The valve 7 is then controlled by the governor 16 within the upper limit set by the screw 57. The valve 103 has a land 104 and a shoulder 114 both cooperating with a bore 105 in a bushing. 106. The bushing is adjustable to determine the clearance between the shoulder 114 and the bore 105 when the valve 17 is in the neutral position and hence the speed drops below the governed speed necessary to release the latch 92. When adjusted, the bushing may be locked by a ring nut 107. The valve 103 has a supply conduit 111 continuously connected with the supply conduit 45. Instead of being positioned only by the hand wheel 60, the primary load limit stop 51 may be adjusted automatically by an operating condition of the power plant, e.g. boiler pressure.