GB595718A - Automatic temperature or pressure control apparatus for operating electric switches - Google Patents

Abstract

595,718. Thermal switches. ROBERTSHAW THERMOSTAT CO. Oct. 20, 1944, No. 20385. Convention date, Nov. 2, 1943. [Class 38(v)] ,In a snap acting thermostat for controlling temperature or pressure automatically, an expansible liquid is stored in a bulb 42 connected by a capillary 40 to a capsule 38, which upon expansion causes the button 44 to swing the U-shaped lever 48 about the knife-edge bearing 52. The lever 48 is joined to the bottom of spring 56, the top of which is hooked over the centre arm of the R-shaped control lever 60, which is borne at is lower extremities by knife edge bearings 65, and supports rearwardly an inverted V-shaped take up arm 74 which carries a contact bridge on. each arm and insulated from it, co-operating with fixed contacts, one of which is 96. When the lever 48 is pushed across a line joining points 52 and 65, the contacts snap open, and conversely when the capsule contracts. A pointer 28 in conjunction with a calibrated scale 26 sets the device to operate at a predetermined temperature by means of the screw 30 which extends through the cover 14 to make contact with the capsule 38. A safety device to open the circuit if the main contacts should stick, comprises a secondary lever 116 carrying a contact bridge 110 insulated from it, co-operating with series contacts 102 and 104, which are opened at a fixed temperature difference above the pre-set operating temperature by the spring 120 when the lever 48 is sufficiently forced over to the right in the Figure to cause the lower end of lever 116 to be disengaged from the frame 10. A manually operated button 138 enables the lever 116 to be returned to its normal latched position in which contacts 102, 104 are closed.