Patent GB-661924-A (GB)
Title: Improvements in or relating to means for controlling the operation of liquid fuel burners
Inventor: SHERLOCK JOHN EDWARD
IPC: F23N5/20
Filed: 1949-03-25
Abstract: 661,924. Thermal switches. BRITISH THERMOSTAT CO. Ltd. March 22, 1950. [March 25, 1949] No. 8227/49. Class 38 (v). [Also in Group XI] In an electrical control apparatus for a liquid fuel burner comprising an ignition device I, Fig. 1, and a fuel pump motor P controlled by electromagnetic relays IR and PR, respectively, thermal switching means H actuated by an electrical heating element He and operable after a predetermined delay period to disconnect the electric supply from the apparatus in the event of the burner failing to ignite, and a thermostatic switching device F responsive to the burner temperature, the closure of a master switch S energizes the thermal switch means H and the relay IR, which latter in turn energizes the relay PR, and the thermostatic switching device F is adapted, when the temperature at the burner rises upon ignition, to de-energize the heating element He and the relay IR whilst maintaining the pump motor relay PR energized. A circuit is established, on closure of the switch S, from electric supply terminals A through contacts Hb, Ha of the switch means H, the switch S, a contact Fa of the device F, the electric heating element He, and the operating coil of the relay IR. Energization of the relay IR closes contacts IRa, IRb to connect, respectively the ignition device I and the relay PR to the electric supply. The contacts PRa and PRb of the relay PR are then immediately closed to energize the fuel pump motor P and to connect the relay coil PR with the open contact Fb of the device F. Should the burner fail to ignite the thermal switching means H is operated after a delay period to move the contact Ha from a terminal Ha<SP>1</SP> into engagement with a terminal Ha<SP>2</SP> to de-energize the relays IR, PR and the element He and connect the electric supply to a visual and/or audible alarm device L. If the burner ignites before said delayed operation of the contact Ha can be effected the heat of the flame actuates the thermostatic switching device F to close the contact Fb and open the contact Fa. The opening of the contact Fa de-energizes. the element He and the ignition relay IR, but the pump motor relay PR remains energized through the main switch S, the contact Fb, and the contact PRb. The thermostatic switching - device F comprises a helical bimetallic element 2, Fig. 2, arranged in the burner flue, and anchored at one end to a tubular housing 3, the other end being secured to a rotatably mounted coaxial rod 4. The latter has fixed thereto a flanged disc 5 having a peripheral projecting peg 6, which when the burner flame is extinguished abuts an extension 7 of the switch contact Fa to close the latter. When the element 2 is heated by the burner flame the disc 5 rotates and the peg 6 occupies the position 6a, Fig. 3. In the event of flame failure the time taken for the peg 6 to move from the position 6a to close the contact Fa constitutes the delay or burner purge period which may be varied by adjusting the position of the extension 7 by rotating a cam 9 against which a pivotally mounted carrier 8 of the contact Fa is held by a spring 10. The contact Fb which has to be closed simultaneously with or before the opening of the contact Fa and opened as soon as flame failure occurs, i.e. as soon as the peg 6 begins to move from the position 6a, is operated by a peg 12 fixed on an inner disc 13 of easily magnetisable material freely rotatable on the rod 4. When the disc 5 rotates clockwise (as viewed in Fig. 3) a torque is imparted by a magnet 14 fixed thereon to the disc 13 causing the peg 12 to abut an extension 11 of the contact Fb to close the latter, lost motion taking place between the discs 5, 13 as soon as the closure is effected. If flame failure occurs the anti-clockwise movement of the magnet 14 will effect an immediate movement of the disc 13 to open the contact Fb, such movement continuing until the peg 12 abuts a fixed stop 15. The electric heating element He is mounted in a tubular housing 20, Fig. 4, and when energized heate a phial (not shown) of fluid which expands through a tube 21 into a chamber 22 to compress a bellows 23. The end plate of the bellows is secured to a rod member 25 which actuates a plunger 26 to move the snap-action contact Ha from the terminal Ha<SP>1</SP> into engagement with the terminal Ha<SP>2</SP>. A reset-button 27 is provided. In the event of leakage of fluid from the chamber 22, the rod 25 retracts and a flange 25a thereon disengages a holding member 28 from the contact Hb so that the latter opens and disconnects the electric supply.