GB1216687A - Improvements in fuel flow control circuits - Google Patents

Abstract

1,216,687. Control circuit for burners. CONTROLS CO. OF AMERICA. 18 Nov., 1968 [28 Dec., 1967], No. 54532/68. Heading F4T. An ignition and fuel flow control circuit for burners comprises an igniter requiring a first operating voltage when no flame is present at the burner and a second, lower voltage in the presence of a flame, an electrically controlled fuel-flow valve arrangement requiring a first current to open it and a second, lower current to maintain it open, electrical control means such that the higher and lower voltages at the igniter produce, respectively, the higher and lower currents in the fuel-flow valve, and valve control means which reacts to the continued presence of the higher current in the valve by closing the valve, thereby interrupting fuel flow. As shown, the voltage pulses for arcing electrodes 10, 12 are supplied by a circuit containing capacitor 24, resistors 26, 28, silicon controlled rectifier 20 and primary 18 of transformer 16. Before ignition occurs, the higher voltage required to produce a spark results in a correspondingly high voltage at base 38 of transistor 34 and this base voltage, controllable by rheostat 44, allows sufficient current to flow through the transistor to open the fuel-flow valve which is operated by solenoid 32. In the presence of a flame at the burner, the required sparking voltage is lower, and the resulting lower current through the transistor is sufficient to maintain open the fuelflow valve. If the fuel fails to ignite, the continued higher current raises the temperature of heater 52, thereby causing thermally responsive switch 54 to open, and the resulting open circuit causes the fuel-flow valve to close. The lower current flowing when the burner is ignited is insufficient to open the circuit in this way. In another embodiment, solenoid 32 is replaced by a solenoid 56 (Fig. 2, not shown) wrapped around the closure element of a fuel valve. The valve is maintained open by the lower current, but in the event of ignition failure the resulting higher current increases the temperature in a heater (64) causing expansion of a bimetal which pushes the valve closure element back into its orifice, thereby shutting off the fuel flow. In a further embodiment, Fig. 3, thermal switch 72 is normally closed, so that as soon as the circuit is powered, the valve controlled by solenoid 68 is opened, whereas the valve controlled by solenoid 66, which is in series with valve 68, is only opened by the higher pre-ignition voltage. However, if ignition does not occur, the continued higher voltage causes a temperature rise in heater 70, resulting in the opening of thermal switch 72, thereby closing the valve operated by solenoid 68.