GB678132A - Improvements relating to push button electric switches - Google Patents

Abstract

678,132. Press-button retractive switches. DOWTY EQUIPMENT, Ltd., and SNELL, M. S. March 14, 1951. No. 6114/51. Class 38 (v). A switch, suitable for controlling the retraction of the undercarriage of an aircraft, may be locked for preventing normal operation and has means whereby it may be operated in an emergency despite the locking action. The push-button 11 comprises two parts 15, 16 carrying contacts 12 co-operating with fixed contacts 13, the inner face of the part 15 bearing on the upper end of a rod 22 having a cylindrical extension 23 slidable on a fixed pin 24. The switch is locked "off", as shown in Fig. 1, when a detent 26 engages a groove 25 in the pin 24 beneath the extension 23, downward movement of which is thus prevented. The switch is unlocked by energization of an electromagnet 27 which retracts the detent 26. In order to operate the switch in an emergency if the detent is operative, the part 15 is rotated through 90 degrees so that a bore 28 therein registers with the rod 22, it then being possible to depress the push-button to close the contacts. On return, of the push-button to its outer position by a spring or other means (not shown), frictional engagement between the bore 28 and rod 22 moves the latter out with the button to prevent return rotation of the button by a spring 18 until a pin is inserted in a hole 29 to push the rod 22 down again. A rubber diaphragm 30 prevents the entry of moisture or foreign matter.