GB638887A - Improvements in or relating to operating systems for aircraft under-carriages - Google Patents

Abstract

638,887. Fluid-actuated valves. DUNLOP RUBBER CO., Ltd., and TREVASKIS, H. W. Aug. 22, 1947, No. 23256. [Class 135] [Also in Group XXXIII] A fluid pressure control valve unit comprises a chamber 3 connected to a source of fluid pressure, a chamber 3a connected to fluid - pressure operated mechanism, a spring- loaded plunger 16 in the pressure chamber, coaxial inlet and outlet valves 9, 10 on a common stem 11 and a tubular seating element 12 for the inlet valve coupled to the plunger 16 so that when the pressure in the chamber 3 exceeds a predetermined value the seating element 12 is lifted to close the inlet valve and open the exhaust valve. The chamber 3a is connected to the fluidpressure operated mechanism by a passage 5 and to exhaust by passages 7, 8 whilst the chamber 3 is connected to the pressure source by a passage 4 leading into a through passage 6. The seating element 12 has a lip 14 and is supported by a ported flanged member 15 screwed to the plunger 16. A spring 19 normally maintains the exhaust valve 10 on its seating 13. The plunger 16 has a perforated rib 17 to facilitate access of fluid to its base, and a cylindrical extension 20 which houses a flanged guide 21, a guide tube 24 and a spring 22 adjusted by a screw 25 in a cover 26. Fig. 2 shows at 42 the control valve of Fig. 1 applied to a fluid-pressure system including a doubleacting jack 30 for operating an aircraft undercarriage 32 held in the retracted position by a catch 46 released by a piston and cylinder device 47. Normally the undercarriage is operated through the transmissions lines 34, 40 or 33, 39 selectively connected to a source of fluid pressure at 41 by a valve 48 controlled by the pilot. If this main operating system fails, the pilot opens a valve 44 to bring in an emergency supply which is connected to the pipes 39, 40 through shuttle valves 37, 38. pipes 35, 36 and 43, and the valve 42 which has an exhaust connection 45 corresponding to the passage 8 and a pipe connection 36 corresponding to the passage 5. Thus, pressure is applied immediately to the lowering end of the jack and to release the catch 46, but the exhaust through pipes 40, 36 is gradual as the valve 10 is not opened until a predetermined pressure has built up in the chamber 3. The Provisional Specification describes a modification in which both the seat and the valve member of the exhaust valve are movable, the valve member thereof being connected to a piston through a lever.