Patent GB-599433-A (GB)
Title: Improvements in or relating to speed control systems for prime movers
IPC: F01D17/26
Filed: 1944-09-14
Abstract: 599,433. Fluid-pressure servomotor-control systems. WESTINGHOUSE ELECTRIC INTERNATIONAL CO. Sept. 14, 1944, No. 17594. Convention date, Sept. 15, 1943. [Class 135] [Also in Group XXVI] A hydraulically operating governor mechanism for controlling the admission of motive fluid to a prime mover in response to pressure changes in a control space or conduit comprises a leak-off valve which controls the pressure in said space and is subject to a force depending on the control pressure, to a force depending on the speed of the prime mover and to a further force due to the pressure in a further space or conduit, the latter pressure being governed by a further leak-off valve carried by a rotatable inertia member and subject to the pressure in the latter space or conduit, to the force of a spring and to forces due to inertia when the speed of the prime mover changes. Figs. 1 and 2 show a system to which the invention can be applied. In Fig. 1, the admission valve-V of a steam turbine P is actuated by a servomotor S under the control of a centrifugal governor G driven through gearing 108, 109 from the turbine shaft 102. A device A responsive to acceleration of the turbine is arranged between the governor G and the servomotor S. The latter comprises a double-acting piston 152 under the control of a piston valve 154 actuated against the pressure of a spring 164 by the pressure within an annular bellows 166, a follow-up spring 169 acting inside the bellows being connected to the valve stem 107 by a lever 171 having a fixed pivot 172. The governor shaft 134 drives a gear pump 113 supplying the hydraulic system through the outlet 114 and carries at its upper end a drum 133 on which the ends of a leaf spring 130 bearing two fly weights 131, 132 are mounted. The central part of the spring 130 engages the stem of a cup-shaped valve 127 slidably mounted in a member 123 mounted in the top of the governor casing 122. The valve 127 seats against the end of a tubular plug 124 adjustable from outside the casing 122 by an eccentric and worm gearing 125, 126. Pressure liquid is supplied to the space 143 above the plug 124 past a metering orifice 142 from a duct 141. The space 143 is connected to the acceleration responsive device A by a duct 144 and a pipe 145. Liquid passing the valve 127 escapes by a duct 135. The device A comprises a cylinder 200 in which a piston 211 with one or more orifices 213 in its end face is movable against a spring 214. Pipes 145, 146 connect the device to the governor and the bellows 166 of the servomotor respectively. An adjustable leak orifice is provided in the base 202 of the cylinder comprising a plug 215 co-operating with a conical member 216 the projecting threaded stem 219 of which is protected by a removable cover 220. Escaping liquid passes to the sump by a pipe 221. Under steady speed conditions the piston 211 remains balanced in one position with a definite leak of liquid through the pipe 221. On the occurrence of speed changes the piston 211 moves to take up a new position of equilibrium following the pressure changes brought about by the governor and produces a transient flow into or out of the bellows 166 the pressure in which depends on turbine acceleration as well as on speed. In the governor mechanism according to the invention which is shown in Fig. 3 the acceleration responsive device is in the form of an inertia governor mounted within the drum 333 of the main governor. The drum 333, the leaf spring 330, the fly weights 331, 332 and the cup valve 327 are substantially as already described. The inertia governor comprises a member 380 fixed inside the drum 333 and supporting on ball bearings 385, a flywheel 386 which has a limited movement with respect to the member 380 defined by a hollow stud 381 a lateral aperture 392 in which is more or less obturated by a cup-shaped valve (not shown) carried by a stud fixed to the flywheel 386. Under constant speed conditions, the parts are maintained in a position in which the pressure within the stud 381 acting to open the cup valve is balanced by a spring 395 anchored to the drum and to the flywheel. An adjustable plug 324 has ducts 341, 344 and a space 343 corresponding to the ducts 141, 144 and the space 143 already described. The metering orifice 142 however is replaced by an annular clearance 342 between a part of the plug and a tubular member 388 connected with the aperture 392 by a bellows 387 and ducts 390, 391. Acceleration of the governor shaft 334 causes the flywheel to lag behind the drum 333 so that the cup valve closes more or less and the pressure backs up in the bellows 387 which moves the valve 327 towards the closed position and thus gives a further impulse to the servomotor. The acceleration responsive device A, Fig. 1, can be omitted from the system if desired. Specification 599,432 is referred to. The Specification as open to inspection under Sect. 91 comprises also a hydraulic governor, Fig. 5 (Cancelled), in which the acceleration responsive device takes the form of an inertia governor 586 of the flywheel type shown in Fig. 3 carrying a leak-off valve on a stud 594, the flywheel in this case being mounted for relative rotary movement on an extension of the shaft 580 of a hydraulic governor pump 511 of the centrifugal type mounted on the turbine shaft. This subject-matter does not appear in the Specification as accepted.