Patent GB-816515-A (GB)
Title: Improvements in or relating to relief valve
IPC: B64D13/02
Filed: 1956-08-08
Abstract: 816,515. Fluid-pressure servomotor-control systems. GARRETT CORPORATION. Aug. 8, 1956 [Sept. 1, 1955], No. 24275/56. Class 135. A pressurized enclosure 10, such as the cabin of an aeroplane, is provided with a relief valve having a closure member 33 opened by cabin &c. pressure when the difference between cabin and atmospheric pressure exceeds a predetermined amount, a control chamber 41 behind the closure member normally being maintained at cabin pressure through a restricted connection 57 but allowed to fall to atmospheric pressure when a pilot valve 42 opens. The valve closure member 33 is cup-shaped, is biased to the closed position by a light spring 60 and is connected to the valve casing by an annular diaphragm 28. The pilot valve 42 is formed with a body connected to its casing by two annular diaphragms 43, 44. The chamber 48 behind the diaphragm 43 is in communication with cabin pressure through a conduit 53, and the chamber 47 between the diaphragms 43, 44 is in communication with the pressure in the control chamber 41 (normally also cabin pressure) through a conduit 52. The chamber 46 beyond the diaphragm 44 is connected to the atmosphere through a pipe 50. When the surrounding atmospheric pressure falls sufficiently to allow the cabin pressure in the chambers 41, 47, 48 to move the body of the pilot valve 42 against the bias of a spring 58, the pilot valve engages a screw 59 which causes it to open, so that the chambers 41, 47 communicate through the pilot valve with the pipe 50 and the atmosphere. The consequential reduction of pressure within the.control chamber 41 enables the pressure in the cabin 10 to blow the valve closure member 33 off its seat against the bias of the spring 60. The position of the screw 59, and hence the pressure differential necessary to open the pilot valve 42, may be adjusted. When the pressure in the cabin 10 has fallen sufficiently, the spring 58 returns the pilot valve 42 to the closed position and cabin pressure forces air through the restricted passage 57 into the control chamber 41 &c. To allow the aeroplane pilot to reduce the pressure within the cabin to that of the surrounding atmosphere at any time, a hand-operated cock (not shown) in a pipe 70 between a controlled pressure release valve 72 and the atmosphere is opened. The pressure relief valve 72 comprises a check ball valve 80 in series with a diaphragm piston 86 formed with a central bleed hole 87 and larger surrounding holes 88. As soon as the handoperated cock is opened, the pressure in the pipe 70 falls to that of the atmosphere, the check ball valve 80 opens and cabin pressure in the control chamber 41 moves the diaphragm piston 86 against the bias of a spring 85 to a position where air can escape only through the bleed hole 87. When the control chamber pressure is sufficiently reduced, the spring 85 moves the diaphragm piston 86 to its open position where air can also escape through the holes 88 to the pipe 70 &c. The control chamber pressure thus continues to fall, but more quickly, and the cabin pressure again blows the valve closure member 33 off its seat. If at any time the pressure in the atmosphere exceeds the pressure in the cabin 10, atmospheric pressure acts on the underside of the annular diaphragm 28 to move the valve closure member 33 to its open position against the bias of the spring 60, where it is retained until the pressures have equalized.