Patent GB-875335-A (GB)
Title: Pressure controlled positioner
IPC: F15B9/08
Filed: 1959-11-12
Abstract: 875,335. Fluid-pressure servomotor control systems; valves. FAIRCHILD ENGINE & AIRPLANE CORPORATION. Nov. 12, 1959 [Nov. 20, 1958; March 13, 1959], No. 38377/59. Class 135. A pressure-controlled positioner comprises a housing 1, Fig. 2, divided into a plurality of chambers 21, 22, 23, 24 by diaphragms 25, 26, 27, the chamber 21 being vented to atmosphere by outlets 28 and the chamber 22 receiving a control pressure fluid through an inlet 29. The diaphragms are connected to a movable valve control member 6 which adjusts the relative positions of the parts 4, 5 of a valve. A second valve member 15 is fixed to the rod 7 of valve member 4, the rod being secured to a diaphragm 8. A fluid pressure supply entering the housing at P acts on the diaphragm 8 to open the valves 15 and 4 and flows into a chamber 20, part of this fluid then passes through the valve 4 to a chamber 43 and hence through passages 44 to the vent chamber 1 and out through the outlet 28. The remainder of the fluid passes to the pipe E and acts on a diaphragm secured to the positioning means, thus the position of this means is controlled by the pressure in the pipe E. The pressure in the pipe E is varied in accordance with the control pressure in chamber 29. If this pressure is increased, the control member 6 is moved upwards, due to the different areas of the diaphragms 25, 26, to reduce the opening of the valve 4, 5 which reduces the bleed from the chamber 20 and increases the pressure in the pipe E. The upward movement of the member 6 increases the loading of a spring J but with subsequent movement of the positioning means a rod I connected to this means also adjusts the loading of the spring to provide a new position of equilibrium for the new control pressure. The chamber 23 may be the control chamber instead of the chamber 22, this provides a reverse direction of movement of the positioning means with increase in pressure. The arrangement of the valve members 4, 15 allows for small fluctuations in the supply pressure entering at P without having effect on the pressure in the pipe E. If this supply pressure increases, the valves move upwards, under movement of the diaphragm 8, and the valve 4 thus increases the opening of the bleed to maintain the pressure in pipe E constant. In a modification, Fig. 3, the fluid pressure supply enters at 115 and passes to chamber 117 where part of it bleeds, past a valve 112, into the vent chamber 122 while the remainder flows through the passage 152 to chamber 126 and acts on a diaphragm 132 to adjust the positioning means 161. The fluid supply pressure is also fed through passage 157 to chamber 124 and acts on diaphragm 130 to provide the loading for the valve control member 135. When the control pressure in chamber 123 varies and adjusts the valve 103 as above, the resulting change in pressure in chamber 126 adjusts the position of the means 161. Movement of the control member 135 varies the horizontal area of diaphragm 130, due to a tapered portion 148, and thus the loading is varied to provide a new equilibrium position. The valves 102, 105 are provided with notches 1141 to allow for a small flow of fluid when the valves are closed.