GB647522A - Improvements in and relating to snap acting control devices applicable to electric switches, fluid control valves, and the like - Google Patents

Abstract

647,522. Thermal switches; snap-action switches; switches actuated by fluid pressure. HENRY, P. Nov. 21, 1945, No. 31372. Convention date, Jan. 15. [Class 38 (v)] [Also in Groups XIII, XXIX and XXXII] A snap-acting device actuated by a change in temperature, pressure or humidity or manually for controlling an electric switch comprises, when actuated by a change in temperature, three bimetallic elements 2, Fig. 7, equally spaced around and secured to a circular plate 6, and resiliently supporting and exerting a radial thrust on a shaft 1. Secured to the upper end of the shaft 1 is a control member 11 of insulating material carrying at its ends contacts 12, Fig. 3, connected by a conductor 13 and arranged to coact with contact members 14 mounted on a mica &c. plate 16 or with stop members 17 also mounted on the plate 16. The plates 6, 16 are arranged for angular adjustment relative to each other to vary the range of operating temperatures and are clamped around their peripheries between the casing parts 31, 32, Fig. 4. Openings in the base of the casing part 32 permit access of the gas whose temperature is being controlled. An increase in temperature of the gas causes the bimetallic elements to exert a tangential force on the shaft and rotate it with a snap-action in a clockwise direction, until arrested by the stops 17, to break contact between the contacts 12 and the members 14. Conversely, a decrease in the temperature of the gas causes anticlockwise rotation of the shaft and electric contact to be made between the conacts 12 and the members 14. When actuated by a change in pressure, the three bimetallic elements are replaced by three Bourdon tubes 52, Fig. 9, supplied with the pressure fluid whose pressure is being controlled through a nozzle 59 and mounted on a ring 56 which is secured to an insulating plate 57 by clamps 58 which permit relative adjustment between the ring and the plate. Otherwise the arrangement is similar to the temperature-actuated device. In another arrangement, the bimetallic elements are replaced by resilient leaf springs 72, Fig. 10, secured to a ring 73 having lugs 81 for attachment to an annular plate 78 of, e.g. melamine or silicone resin. An actuating member M arranged to coact with one of the springs exerts a tangential thrust on the shaft 71 to rotate it anticlockwise and break electric contact. On removal of the member M from contact with the spring, the resilience of the springs rotates the shaft clockwise to make electric contact. The member M may be actuated manually or in response to a change in pressure, temperature or humidity. In a modification, the control member 11 is provided with double contacts at either end and the stops 17 are replaced by contact members so that the switch may function as a double-throw switch.