GB1269084A - Pneumatically-operated burner control system - Google Patents

Abstract

1,269,084. Controlling burners by pneumatic logic-circuits. ROBERTSHAW CONTROLS CO. 31 March, 1969 [1 April, 1968], No. 16786/69. Heading F4T. A system for controlling the flow of fuel to a burner 12 comprises a valve 36, 37 operated by a first pneumatic actuator 38 adapted to be connected to a vacuum pump 19 only after a further pneumatic actuator 52 has been connected to the pump 19 to bring an ignition coil 44 to an ignition-temperature . Clothes drying apparatus is described in which a motor 15 operates the pump 19 and is adapted to be connected to terminals L 1 , L 2 when a timer switch 34 and a door-switch 22, are closed, a further switch 20 in the motor-circuit being normally closed. The pump 19 is connected to a valve 68, 71 operated by a bimetal strip 67 responsive to the temperature generated by the burner 12, the valve 68, 71 being connected to a further valve 60, 63 operated by a bimetal strip 59 responsive to the temperature of the ignition coil 44. The further valve 60, 63 is operative to connect the pump 19 to the further pneumatic actuator 52 to close a switch 49 and thus connect the ignition coil 44 across the terminals L 1 , L 2 . A conduit 72 connects the valve 68, 71 to a logic memory unit 74, and to a logic not unit 77. The further valve 60- 63 is also connected to the memory unit 74 and the not unit 77. A logic and unit 105 is connected to the first pneumatic actuator 38 by a conduit 110, to the not unit 77 by a conduit 107, and to the memory unit 74 by a conduit 103. At the start of operation, the valves 68, 71 and 60, 63 are open and vacuum is thus applied to the memory unit 74 and to the not unit 77, actuation of these units causing the and unit 105 to connect the first actuator 38 to atmosphere via the conduit 107, the not unit 77, and a bleed 117 therefrom. At the same time the further actuator 52 operates the ignition coil 44 which, upon reaching an ignition temperature, causes the valve 60, 63 to close, a check valve 75 maintaining the vacuum in the memory unit 74. Closure of the valve 60, 63 also de-activates the not unit 77 which then connects the conduit 107 (and hence the actuator 38) via the conduit 72 to the pump 19 to open the fuel valve 36, 37. The coil 44 is deactivated on closure of the valve 60, 63 but then valve is maintained open by the heat of the ignited burner 12. An accumulator 94 is connected to the pump 19 each time the further actuator 52 is so connected, and is, after a number of ignition attempts, operative to open the switch 30 and deactivate the entire system. Details of the operation and structure of the memory unit 74, the not unit 77, and the and unit 105 are given (Fig. 2).