Gas motor driven positioner

摘要

924,856. Fluid-pressure servomotor control systems; valves. GRINNELL CORPORATION. May 5, 1960 [Sept. 25, 1959], No. 15893/60. Class 135. In a gas-motor driven device for positioning fluid handling equipment, e.g. a pipe 10, Fig. 1, the pipe may move up or down due to thermal expansion but is supported with a substantially constant force by a support 12-18 positioned by the reversible motor 64. Thus, if the pipe tends to move upwards, the load is relieved on Bellville washers 68 so that screwed spindle 28 rises and through lever 74 actuates a piston valve 82 controlling the gas motor which, through reduction gearing 42 and pin-and-slot mechanism 36, rotates the screwed spindle 28 to lift the supports 12-18 and maintain the support load on the pipe. The increased load on the Bellville washers allows the spindle and lever 74 to recentre the piston valve. The whole device is enclosed in a gas-tight casing into which the gas motor exhausts and is provided with a vent or gas inlet inhibitor 86 or vents around those parts of the device passing through the casing. In another embodiment, a firm thrust bearing replaces the Bellville washers and the temperature of the pipe is detected by a feeler tube coiled around the pipe and connected to a bellows which moves a lever positioned between two lift valves loaded to open. Closure of one of these valves moves a piston valve against a spring to allow gas pressure to position piston valve 82 controlling the motor. The lift valves move in an inner casing in the main casing, and the inner casings may be reversed so that the lift valves are loaded to close. In the embodiment of Fig. 7, increase in the upward load of the pipe on support 290 tends to reduce the pressure of fluid 292 beneath a piston 288 connected to support 290. This pressure reduction is communicated to a Bourdon tube 306 which moves a valve 298 allowing pressure from 308 to act via 310 to position a piston valve 314 so that the pressure drives an irreversible gas-motor 296 driving a pump 294 whereby fluid is pumped beneath piston 288 to lift it and maintain the supporting load on the pipe constant. The increased pressure acts in the Bourdon tube to recentre valve 298. Should the pipe load increase downwardly, the increased pressure beneath piston 288 is relieved through a relief valve 330. Should the pressure beneath the piston decrease sharply due to a leak, a brake 336 is urged on to a wheel 334 having a threaded engagement with the piston, whereby the piston is prevented from dropping the pipe load. Specification 924,857 is referred to.