GB482611A - Improvements in control systems - Google Patents

Abstract

482,611. Electric control systems. BAILEY METER CO. Nov. 27, 1936, No. 32513. Convention date, Dec. 18, 1935. [Class 40 (i)] [Also in Groups XXIX, XI, and XXXV] A vapour generator of the drumless forced-flow type in which liquid under pressure is received at one end and superheated vapour only is delivered at the other end, excess liquid being extracted at an intermediate point, is controlled by, measuring the vapour outflow and utilizing such measurement to vary the supply of liquid under pressure to maintain it a predetermined amount in excess of the vapour outflow. Fig. 3 shows the arrangement when air pressure servomotors are used in the control system, but these may be replaced by electrical devices associated with oil servomotors. The pump 289 delivering the feed water, the fuel oil pump 290 and the air blower 288 are driven by a common auxiliary turbine 287 supplied with low and high pressure steam under the control of a valve device 39. This device is actuated by air pressure acting on a diaphragm 40 under the control of an auxiliary valve 41 subject to the pressure across a throttle valve 17 in the water inlet pipe. This valve is actuated by a diaphragm subject to the control of an aggregate relay 47 itself under the control of devices responsive to the flow in the vapour outlet and the level in the separator interposed between the generating and superheate sections. The flow responsive device comprises a liquid sealed bell coupled to an auxiliary valve 43 and actuated by the pressure differential across a restriction 79. The level responsive device comprises an auxiliary valve 48 coupled to a float working in one arm of a mercury U-tube 29 connected by pipes to the top and bottom of the separator 232. This separator has a normal discharge 2 and a supplementary passage controlled by a valve 3 opened by air pressure under the control of the float-actuated auxiliary valve when the level in the separator rises unduly. A byepass valve 18 across the water pump and a damper in the intake to the blower are operated by power devices controlled by an auxiliary valve 69 operated by a Bourdon tube subject to vapour outlet pressure. The arrangement is such that a sudden and material drop of pressure, consequent on an increased demand, causes both valve 18 and damper 15 to open, the opening of the valve 18 causing the auxiliary turbine to speed up so that the fuel and air supplies are increased without an immediate increase in the liquid supply. Flow meters 14 and 16 comprising liquid sealed bells subject to the pressure differentials across conduit restrictions measure the air and fuel oil flow respectively. The indicating levers of these meters are coupled by links to a floating lever 71 coupled to an auxiliary valve 73 controlling a relay valve 74 itself controlling the supply of compressed air to a diaphragm operating a throttle valve 13 in the oil fuel line. In the modified arrangement in which the air actuated apparatus is replaced by electrical apparatus, the auxiliary valves are replaced by electron-discharge devices having a variable area electrode, actuated by diaphragms, bellows or Bourdon tubes. These devices are electrically connected through relay panels to operating units including a unidirectional electric motor. The lay-out of one of the relay panels is shown in Fig. 9 and comprises an electron-discharge device 109 adapted to control the flow of a pulsating direct-current for the speed control of a motor 110. The control of such current is affected by regulating the percentage of time during which the device 109 is allowed to conduct, this being done by impressing upon the grid of the device 109 the sum of an A.C. and a D.C. voltage. Through the action of a phase shifting bridge 106, 107, 108, the A.C. lags with respect to the plate voltage, so that the point in the cycle at which the grid voltage reaches the threshold valve and allows the device to conduct may be varied by varying the D.C. voltage. Such variation is produced by varying the effective area of the anode of the electron-discharge device 92 by mechanically moving the arm 103. The motor 110 drives a rotary pump housed in a spring- loaded piston coupled to the valve or damper to be operated.