GB589873A - Improvements in or relating to safety controls for fuel burners - Google Patents

Abstract

589,873. Burners, controlling. MAY, P. (Robertshaw Thermostat Co.). Nov. 16, 1944, No. 22733. [Classes 75 (i) and 75 (iii)] [Also in Group XXIX] In an electrically controlled burner in which a solenoid valve controlling the fuel supply is controlled by an electric resistance element heated by the main or pilot burner means are provided for closing the valve if the resistance element circuit fails. In the burner shown the manual or thermostatic opening of a ;gas valve 14 completes the secondary circuit of a mains energized transformer 24 to a bridge having in one arm a series resistor 38, a pilot burner igniting coil 40, and a delayed action switch 42, in the second arm an electromagnetically operated valve 16 arranged between the valve 14 and the main burner 10, in the third and fourth arms respectively resistors '58, 66, having normally low resistances and . positive temperature coefficients of resistance, and in the detector arm a cut-out 70, preferably of the thermal type, having a time lag in operation. The secondary circuit also includes a coil 92 which opens the switch 42 and a switch 76 initially short circuiting the valve 16 with time delays of say 18 and 13 seconds respectively. When the valve 14 is opened gas can pass to the pilot burner 18 but is prevented from passing to the main burner 10 by the valve 16. A large current initially passing. through the out-out 70 decreases as the resistors 58, 66 become heated, the resistors 58 by the flame from the pilot burner and the resistor 66 by the current passing through it, and the current is further diminished on the opening of the switches 42, 76 when the valve 16 opens and the burner 10 is ignited. The current through the cut-out 70 is then insufficient to cause its operation unless the resistor 58 is fractured. Should the pilot burner become extinguished the resistor 58 cools and the current through the valve 16 is insufficient to retain it in the open position. A manually operated switch 82 is provided to allow the pilot burner to be ignited by a match if the ignition coil 40 fails. Specification 572,130 is referred to.