GB698532A - Fluid-pressure actuated control system - Google Patents

Abstract

698,532. Fluid-pressure servomotor-control systems. GASAIR CORPORATION. Oct. 22, 1951 [Jan. 11, 1951], No. 24629/51. Class 135 A fluid-pressure control system comprises a pressure-responsive member e.g. diaphragm 34, Fig. 3, in which is mounted a pilot valve comprising a casing 40 with an inlet below, and an outlet above, the diaphragm, the inlet and outlet being controlled by spaced closure members 65, 64, respectively, and when the controlling pressure applied to the diaphragm through a conduit 26 reaches a pre-determined minimum, inlet closure 65 is opened and the pressure fluid flows to the control chamber 81 of a further pressure-responsive member e.g. diaphragm 80, the chamber 81 being vented past the now opened closure 64 when the pressure acting on diaphragm 34 attains a predetermined maximum. Closures 65, 64 are urged to the closed position by a common spring 66, and each closure carries a tappet 67, 68 which opens the appropriate closure by abutting against a fixed part of the device as the diaphragm 34 moves. The point at which closure 64 opens can be varied by adjusting the position of a block 72 forming the abutment for tappet 67, the block being carried on a stem 73 adjustable by a screw 76. Rotation of a handwheel 49 rotates a screw 46 to move a nut 45 up or down and so vary the loading effect of a spring 43 on the diaphragm 34. To prevent nut 45 from rotating, it is made hexagonal in shape and fits closely in an hexagonal casing. Diaphragm 80 actuates a spring-loaded valve 91 through a tappet 87, this valve serving to control the supply of pressure fluid from a line 23 to a line 24. The above system is shown applied to the control of the pressure in a main 20, Fig. 1, which receives combustible vapour from a supply 10, this supply passing a cut-off valve 13, an aspirator 16 which draws in air past a check valve 18, and a venturi 19 which reduces the pressure somewhat. The high pressure vapour is also supplied past a pressure reducer 22 to the line 23, and line 24 leads an actuating pressure to a regulator 12 controlling the valve 13. The space under diaphragm 80 is kept at the outlet pressure above diaphragm 34 by means of a passage 83, and the gas vented by the pilot valve is led off through a pipe 102 to a burner 100. The nature of the flame at this burner gives an indication of any fault that might develop in the control system.