GB702545A - Improvements in or relating to liquid-liquid interface position controllers or indicators - Google Patents

Abstract

702,545. Automatic liquid level control systems. NATIONAL RESEARCH DEVELOPMENT CORPORATION. March 24, 1952 [March 19, 1951], No. 6499/51. Class 38 (4) Control or indication of the position of an interface between liquids of different densities involves the derivation of three pressure differences from four conduits, two terminating in the denser liquid and two in the less dense liquid. In a liquid-liquid extraction column 1, Fig. 1, the denser liquid enters at 37 and leaves at 19a, while the lighter liquid enters at 38 and leaves at 39. To maintain constant the level of the interface 6 a valve 19 controlling the outflow of denser liquid is automatically adjusted in response to change of level as detected by pressure differences between conduits a, b, c, d, the upper ends of which are supplied from a compressed air source through a reducing valve 7 and the lower ends of which are open and equally spaced in a vertical direction. A transducer A comprising a differential bellows with an inductive type pick-off. Fig. 2 (not shown), is associated with conduits a and b to produce a voltage output 33, 34 dependent on the density of the lighter liquid. A similar transducer C associated with conduits and d produces a voltage output 33, 34 dependent on the density of the heavier liquid. A third transducer B associated with conduits band c produces a voltage output 33, 34 dependent on both densities and on the level of the interface. The voltages from transducers A and C are applied in opposition to a potentiometer D2 the resultant voltage from the slider of which is applied in opposition to the voltage from transducer B to a current responsive device. 16, which drives the potentiometer slider until balance is obtained. The slider position is then representative of the level of the interface regardless of the liquid densities. Device 16 controls valve 19 either through a pneumatic valve 18 or polarized relays controlling a motor. In a modification differential bellows are associated with the three conduit pairs and the movements of two bellows are compounded to move a contact relative to a pair of opposed contacts moved by the third bellows. The contacts control a reversible electric motor operating valve 19. An air nozzle, palette and air reaction bellows may replace the two-way switch if valve 19 is airoperated.