Patent GB-800825-A (GB)
Title: Improvements in or relating to fluid pressure apparatus for measuring, recording and/or controlling the magnitude of a physical quantity
Inventor: WOODLEY HAROLD JOHN
IPC: B01D3/42
Filed: 1955-11-01
Abstract: 800,825. Fluid-pressure servomotor control systems. SHELL RESEARCH, Ltd. Oct. 31, 1956 [Nov. 1, 1955], No. 31181/55. Class 135. The operating pressure at the top of a fractionating column 1 is maintained at a given absolute pressure by adjusting a throttle valve 2 in a conduit conveying vapour from the top of the column 1, the adjustment being effected by apparatus consisting of a primary monometer 3 having one arm 3a, which incorporates a reservoir 5 connected to the top of the column 1 whilst a tube 6 enters the other arm 3b to a depth which is adjustable to set the lower limit of the range of variation of column pressure. The other end of the tube 6 is connected to a conduit 8 through which compressed air under the control of a manual throttle valve 9 passes to one column of a secondary monometer 10 having its other column open to atmosphere, the air being at a greater pressure than the vapour in the column 1. At the commencement of operation the lower end of the tube 6 is open to atmosphere so that both of the secondary monometer columns are of equal height; as soon as the lower end of the tube 6 is covered, the air pressure in the latter rises and causes inequality in the heights of the secondary monometer columns, which through a float mechanism 11 on top of the atmospheric column may produce deflection of a pointer that indicates pressure variations in the fractionating column 1. The pointer will indicate absolute pressures if barometric-pressure compensating means, not shown, are provided. The secondary monometer may be replaced by a diaphragm device, not shown. The float mechanism 11 actuates a transmitter 12 which determines the air pressure in a two-part conduit 13 having a range of variation six times that in a conduit 8, the conduit 13 communicating with a receiver 14 via a barometric-pressure compensator 15. The receiver 14 includes a pen recorder whilst a controlling apparatus, such as a pneumatic servomotor, not shown, is coupled to the valve 2 by a conduit 16 to adjust the valve and reduce any deviation of the fractionating-column pressure from the given valve. The barometric pressure-compensator 15, which subtracts pressure from those in the upper part of conduit 13 representative of variations in atmospheric pressure consists of a pivoted beam 20 subjected at its ends to upward thrust by bellows 20a, 20b, the latter being connected to the upper part of conduit 13 and the former carrying air pressure from a known transmitter 22 in the same pressure range as that existing in the conduit 13, the transmitter being responsive to atmospheric pressure. The beam 20 actuates a further transmitter 23 which is connected to the receiver 14 via the lower part of conduit 13. If gauge pressure only is to be controlled the compensator 15 may be omitted. The apparatus may control temperature or fluid flow by converting the variations in physical characteristic into pressures. In the case of a temperature control the conduit 16 is dispensed with and a converter 25 is connected between the column 1 and arm 3a, and a conduit 26 from the receiver 14 is connected to a temperature-controlling device, not shown. The apparatus may be used for any combination of the three functions of measuring, recording and controlling.