GB649194A - Improvements in or relating to snap-action electric switch devices - Google Patents

Abstract

649,194. Thermal switches; actuation of switches. ROBERTSHAW-FULTON CONTROLS CO. Feb. 24, 1948, No. 5528. Convention date, March 14, 1947. [Class 38(v)] A switch is tripped by a temperature or pressure sensitive means which increases the compression of a spring before unlatching an operating member, so that the switch contacts are opened with a snap action. The switch comprises three pivoted levers; the first, a lever 28, is pivoted at 32 and has an insulating strip 26 carrying a loosely mounted contact member 24; the second, a lever 40, is also pivoted at 32 and has an extension 44 forming a latch member; and the third, a lever 48 is pivoted at 52 and has a latch 60 engaging the member 44. The contacts 20, 24 are held closed by a spring 56 mounted between the levers 28, 40, when the member 44 on the lever 40 is retained by the latch 60, so as to hold the lever 40 against the pressure of a spring 54 mounted between the levers 40, 48. A distortable capsule 62, which is connected by tube 66 to a fluid containing temperature sensitive bulb or to a source of pressure, has a button 68 engaging an adjusting screw 70 on the lever 48. Thus, as the pressure in the capsule 62 increases, the spring 54 is at first compressed to a greater extent, so that when a predetermined temperature or pressure is reached and the latch 60 is disengaged from the member 44, the lever 40 is moved rapidly by the spring 54 and its end 47 strikes the lever 28 to open the contacts with a snap-action. The contacts 20, 24 remain open until the levers are restored to their original positions by means of a re-set button 72, which when depressed manually, moves the lever 40 to a position where it is relatched if the pressure in the capsule has fallen sufficiently. The button 72 is carried by the switch cover 12 which has an insulating lining 22 surrounding the contact members.