GB619803A - Improvements in thermal electric switches - Google Patents

Abstract

619,803. Thermal switches. WILCOLATOR CO. Dec. 24, 1946, No. 37904. Convention date, Aug. 20, 1943. [Class 38 (v)] A thermal switch is actuated by a snap-action spring 26, 28 when permitted by the contraction of a bellows 8, and re-set manually by a plunger 36. The spring 26, 28 is E-shaped, the ends of the outer limbs 26 being secured by screws 27 and the bowed centre limb 28 having a knife-edge engaging a stud 29 on a switch arm 6. The limb 28 always tends to turn the arm 6 anti-clockwise on a knife-edge about a stud 7, a stop 34a limiting this movement. A bracket 30 attached to the common limb of the E-spring 26, 28 extends through an opening in the arm 6 and loosely carries a contact block 31 having contacts 33 co-operating with fixed contacts 34. The bellows 8, actuated by liquid in a chamber 9 contains a plug 13 adjustably screwed to a rod 16 freely passing through the arm 6 and engaging it by a flange 19. The rod 16 has lugs 20 slidable in grooves in a spindle 22, rotatable through one revolution by an adjusting knob 23 to vary the distance between the flange 19 and the plug 13 and hence the operating temperature. A rise in temperature causes the bellows to contract, compressing a spring 17, and moving the flange 19 to the right, thereby permitting the arm 6 to be rotated counterclockwise by the spring 26, 28. The limb 28 moves between the limbs 26 through a deadcentre position whereby the bracket 30 snaps to the left and opens the contacts 33, 34; the block 31 being arrested by stops 38. If now the temperature falls, the spring 17 is insufficient to return the spring 26, 28 and reclose the circuit, this being effected by pressing the plunger 36; the plunger can also be pulled to open the circuit. Specification 508,926 is referred to.