Patent GB-819532-A (GB)
Title: Improvements in or relating to pneumatic actuator
IPC: F16K31/00
Filed: 1956-07-27
Abstract: 819,532. Fluid-pressure servomotor control systems. GARRETT CORPORATION. July 27, 1956 [Sept. 2, 1955], No. 23263/56. Class 135. A pneumatic actuator for use in an aeroplane comprises a first movable wall means cooperatively coupled with the actuated device and forming one side of a first chamber, means introducing pneumatic pressure to the first chamber, valve means for regulating the pressure in the first chamber, and a second movable wall means forming one side of a second chamber and co-operatively coupled with said valve means, pressure control means provided for regulating the pressure in one of said chambers to actuate the device, and coupling means provided between the first movable wall means and the valve means, for causing the valve means to operate in a follow-up manner upon response of the first movable wall means to pressure changes occasioned by adjustment of the pressure control means. In one form, a pressure inlet pipe 25, Fig. 1, supplies compressed air through a restricted orifice 26 to a cylinder 23 containing a motor diaphragm 21. A remotely positioned bleed-off regulator valve 27 is connected by a pipe 24 to the cylinder 23. Hand operation of a knob 31 co-operating with a graduated scale adjusts the compression of a spring 29, biasing a disc having a central hole 33 engaging a ball 32, to control the pressure in the pipe 24 required to act on a diaphragm 28 and move the disc away from the ball. The air thus released bleeds off through the hole 33 and a hole 35. The motor diaphragm 21 is biased against the pressure of the compressed air in the cylinder 23 by a spring 22 and engages a two-part negative feedback valve 36. Compressed air from the inlet is fed through a branch pipe 38 and a reduced bore 39 to a passage 40 adjustably closed by one element 20 of the feedback valve 36. Opening the passage 40 supplies compressed air to a chamber 16 containing a motor diaphragm piston 15 connected by links 13, 14 to a controlled valve 11. The negative feedback valve 36 is connected by a tension spring 19 to the diaphragm piston 15. Downward movement in the Figure of the diaphragm 15, as pressure builds up in the chamber 16. against the bias of a spring 18, causes the spring 19 to act upon the negative feedback valve 36 to partially close the passage 40, and simultaneously to move a neck 42 of the feedback valve into a.passage 37 open to the atmosphere. Pressure in the chamber 16 accordingly finally stabilizes at a position determined by the setting of the remotely positioned regulator valve 27 controlling the motor diaphragm 21. The controlled valve 11 is situated in a pipe 10 through which hot fluid is passed in the direction shown by the arrows. Variation in the position of the butterfly valve 11 due to aerodynamic or other effects reacts through the diaphragm piston 15 on the negative feedback valve 36, which automatically adjusts the pressure in the chamber 16 to restore the original position. A pipe 56 supplies cold fluid to the pipe 10 where it is mixed with the hot fluid. The resulting mixture passes the heat-sensitive elements 54, 55 of a thermally operated valve 44 which modulates the pressure in the chamber 16, and accordingly the position of the diaphragm 15, butterfly valve 11, &c., in response to variations in mixture liquid temperature. A pipe 42a connects the chamber 16 to a chamber in the thermally operated valve 44 containing a diaphragm 45. A bleed hole 50 connects the two opposite sides of the diaphragm 45. The heat-sensitive elements 54, 55 of the valve operate through a stem-mounted valve ball 52 to vent the lower side of the diaphragm 45 to the atmosphere through a passage 58. The diaphragm 45 controls a stem-mounted ball 46 closing a passage 47 through which the chamber 16 and pipe 42a can be connected to the atmosphere. When the temperature of the heat-sensitive elements 54, 55 increases above a predetermined point, the lower side of the diaphragm 45 is vented to the atmosphere, the stem-mounted ball 46 opens the hole 47, pressure in the chamber 16 is reduced, and the position of the butterfly valve 11 correspondingly adjusted. In a modification, Fig. 2, a compressed air supply pipe 71 feeds through a restricted orifice 79 to a<SP> </SP>pipe 61 connected to a chamber 62 on one side of a diaphragm piston 63. The pressure in the pipe 61 &c. is adjusted by a remotely positioned manually controlled bleed-off regulator valve 60 similar to the valve 27. The diaphragm piston 63 acts upon one end of,a negative feedback valve 66 in the compressed air supply pipe 71. An extension 72 of this pipe conducts compressed air to a chamber 73 containing a diaphragm piston 74 connected by a rod 75 to the controlled mechanism. A spring 77 biases the diaphragm piston 74 against the pressure of the compressed air in the chamber 73, and a compressed spring 67 connects the diaphragm pistons 63, 74. A bleed-off hole 76 allows compressed air to escape continually to the surrounding atmosphere. Adjustment of the control valve 60 varies the position of the diaphragm 63, the negative feedback valve 66, the diaphragm 74 and the rod 75. Reaction back from the controlled mechanism upon the control rod 75 automatically adjusts the position of the negative feedback valve 66 to vary the pressure in the chamber,73, and accordingly restore the original position. In another modification, pressure inlet pipe 90, Fig. 3, supplies compressed air to a casing in which is mounted for axial movement a rod 87 formed with conduits 92, 88 leading to a negative feedback valve 94 .. 97. A bleed-off hole 93 in the rod 87 leads compressed air to a chamber 82 containing a motor diaphragm piston 83 fast with the rod 87 and biased downwardly by a spring 86a. The pressure in the chamber 82 is adjusted by a remotely positioned manually controlled bleedoff regulator valve 81, similar to the valve 27. The negative feedback valve comprises a ball 95 and stem 103 in the rod 87, biased to the closed position by a spring 96 and open when the stem 103 engages one side of a motor diaphragm piston 99. Compressed air then passes from the conduit 88 across the ball 95 to an outlet 97 and into a chamber 98 in which is mounted the diaphragm piston 99. A pipe 89a connects the chamber 98 to the upper end of the housing part supporting the rod 87. A bleed-off hole 100 allows the continual escape of compressed air from the chamber 98. A rod 104 connects the diaphragm piston 99 to the controlled mechanism. The position of the rod 104 and the controlled mechanism is adjusted by the manually operated regulator valve 81 controlling the pressure in the chamber 82. This adjusts the position of the diaphragm piston 83 and the rod 87, and thus the point at which the negative feedback valve 94 ... 97 is opened by the diaphragm piston 99. Reaction back on the rod 104 and diaphragm piston 99 from the controlled mechanism automatically operates the negative feedback valve in such a way as to adjust the pressure in the chamber 98 and restore the original position. In a final modification, a pressure inlet pipe 120, Fig. 4, supplies compressed air through a pipe 123 and two small holes 124, 125 to the upper and lower sides of a piston 127 in a cylinder 126. The piston 127 is mounted for limited axial movement relatively to its connecting rod 128, and is held locked in position within its cylinder 126 by a number of radially extending fingers 132, 133. Radial springs 134, 135 connect the fingers 132, 133 to the piston 127, the inner ends of the fingers engaging grooves 143, 144 in the connecting rod 128. On movement of the piston 127, the outer periphery 136 or 137 of the piston engages the appropriate fingers 132, or 133 to disengage them from the inner wall of the cylinder 126. Further movement of the piston 127 relatively to the rod 128 then engages the inner piston hub 130 with the inner end of the appropriate fingers, and moves the connecting rod 128 and the controlled mechanism associated therewith. Differences in pressure above and below the piston 127 are obtanied by the setting of a negative feedback valve 149 which alternatively opens one or other of a pair of passages 146, 148 at the end of conduits 145, 147 in the connecting rod 128. The conduits 145, 147 lead to the upper and lower sides of the piston 127, respectively, and when open are connected through a port 161 in the valve 149 to the surrounding atmosphere. The negative feedback valve 149 is connected to a diaphragm piston 150 in a chamber 160 to which compressed air is supplied from the inlet pipe 120 via a thermally actuated pressure valve 119. Heat-responsive elements ] 08, 109 of the thermally responsive valve are situated in a fluid flow line and control the closure of a vent aperture 113 by a valve ball 112. A diaphragm piston 116 in the thermally actuated valve is formed with a central bleed hole 117. Compressed air from the downstream side of the supply line 120 enters the upper chamber 118 containing the diaphragm 116, bleeds through the hole 117 to the lower chamber 114 and then escapes or not to the atmosphere through the hole 113 and a hole 115. The setting of the pressure supply valve 119 and the position of the negative feedback valve 149 accordingly varies with the temperature of the heat-responsive elements 108, 109, which therefore also determines the position of the connecting rod 128 and the controlled mechanism associated therewith.