GB723537A - Improvements relating to fluid-operated automatic regulating or control apparatus - Google Patents

Abstract

723,537. Fluid-pressure servomotor-control systems. ELECTROFLO METERS CO., Ltd., and ENGEL, F. V. A. E. Dec. 11, 1952 [Sept. 11, 1951], No. 21385/51. Class 135. In a fluid-operated automatic control apparatus of the kind in which variations in the value of a measured quantity such as temperature, pressure, ion concentration, &c., cause variations in the flow through one or more nozzles which in turn cause variations in the static pressure in one or more control chambers, the static or control pressure, which is utilized to actuate a regulating unit such as a valve, is controlled by two buoyantly suspended or substantially freely movable co-operating members arranged adjacently to one another, both of the members being nozzles, or one a nozzle and the other a baffle body. Both members are buoyantly suspended in coaxial relation by one or more diaphragms or bellows. In Fig. 1, the lower buoyantly suspended member which is formed as a nozzle 8 supplied with compressed air through a duct 7<SP>1</SP> is utilized to introduce a derivative action such as rate of change action or control. A nozzle 2 buoyantly suspended by three diaphragms so as to form two chambers 3, 4 co-operates with the nozzle 8 and a stationary nozzle 1. The nozzles 1 and 8 may be supplied at equal or unequal rates through adjustable valves or like throttling devices. The stationary nozzle 1 may be axially adjustable. A reference pressure corresponding to the datum value of the variable is applied to the chamber 3 through a pipe 5. A pressure directly related to the variable quantity is applied to the chamber 4 through a pipe 6. If the pressures are not in balance the nozzle is moved to cause variation of pressure in a chamber 9 and this variation is applied through a pipe 10 to the regulating device directly or through a servomotor. The chamber 9 has an adjustable bleed 14. A chamber 15 above the diaphragms may be connected to atmosphere directly at 14<SP>1</SP> or through an adjustable bleed. The nozzle 8 is buoyantly suspended by diaphragms forming a chamber 7 which separates the chamber 9 from a lower chamber 11 connected to the chamber 9 by a pipe 12 having an adjustable or a fixed throttle device 13 or both. Pressure changes in the chamber 11 slowly follow those in the chamber 9. Any disparity in the pressures results in a movement of the nozzle 8 which thus introduces a rate of change component into the regulation. In a modification, the nozzle 2 is replaced by a solid body the ends of which co-operate with the nozzles 1, 8. In Fig. 3, the nozzles 1 and 8 are dispensed with and the movable nozzle 2 cooperates with a fixed baffle 19 and a movable baffle plate 18 resiliently supported by a diaphragm 17. The only supply of compressed air is through a pipe 1. In a further modification the nozzle 2 is supported by opposite pairs of concentric bellows. The buoyantly suspended control elements such as the nozzle 2 may be operated electrically instead of pneumatically in which ease they are of soft Swedish iron and operate in the field of a solenoid, the current in which represents or itself constitutes the variable quantity to be regulated. The arrangements described are adaptable to a simple proportional control or to integral control or to a combination of both.