GB875126A - Improvements relating to hydraulic control systems - Google Patents

Abstract

875,126. Valves. FAIREY CO. Ltd. Dec. 10, 1957 [Sept. 10, 1956]. No. 27678/56. Class 135. An hydraulic control system for controlling the supply of emergency pressure liquid from an inlet pipe 11 to a jack 1 operating aircraft control surfaces, undercarriage &c. which is normally supplied with liquid from a pipeline 5 controlled by a valve 2 operated by the pilot's control member 4, comprises a control valve assembly consisting of tandem valves 16, 18 of which the former, loaded by a spring 28, is normally closed while the latter is normally open, and a hand lever 40, operation of which through a cam 41 and ball follower 42, first closes valve 18 and then opens valve 16. As shown, valve 16 is connected to jack 1 by a pipeline 15 incorporating a shuttle valve including a free piston 13 normally urged to the left of its cylinder 12 by pressure in pipeline 7. Any leakage of liquid past piston 13 escapes via pipeline 15 and a passage 30 in plunger 22 to the main return line 10, so preventing any pressure build-up in line 15. Upon failure of the main pressure supply operation of handle 40 first closes valve 18 to isolate line 15 from return line 10, and then opens valve 16 against spring 28 to allow the emergency power liquid to pass from line 11 to line 15, move shuttle piston 13 to the right and thus operate jack 1. The end of valve 16 forms a piston 43 working in a cylinder 44 connected by a line 47 to return line 10, so that any pressure build-up in the latter tends to maintain valve 16 closed. This arrangement only permits one-way emergency operation of jack 1, e.g. for operating landing flaps, but in a modification, Fig. 2 (not shown), two-way operation is permitted by omitting the shuttle valve and connecting line 15 directly to control valve 2.