GB1032077A - Apparatus for controlling furnaces - Google Patents

Abstract

1,032,077. Safety control of burners. LANDIS & GYR A.G. Aug. 14, 1964 [Aug. 21, 1963], No. 33352/64. Heading F4T. [Also in Division G1] A flame safety control apparatus for a furnace burner comprising a photo-electric monitor 6, a thermal delay safety relay 7, a power switching relay 15 and a thermal relay 20 provides a scavenging period before fuel is supplied to the burner and an ignition period which extends for a time after the flame monitor has responded to the presence of a flame. In operation, when a thermostatic switch 11 closes, a burner motor 33 is energized and conveys air to the furnace, an ignition transformer 26 and the thermal relay 20 are energized and after 20 seconds the relay switches over the two-way contact 21 to energize the safety relay 7 and the power switching relay 15. The power switching relay 15 closes a contact 19 to open a by-pass fuel valve 31 which supplies a small flow of fuel to the burner. If ignition occurs, the flame monitor 6 opens contacts 23, but the ignition transformer continues to be energized through a parallel path including a contact 17 closed by the power switching relay 15 and a contact 29 closed by the thermal relay 20. The flame monitor also operates a two-way switch 22 to short-circuit the safety relay 7. A holding contact 16 keeps the power switching relay 15 energized. The thermal relay 20 opens its own energizing circuit at the two-way contact 21 and cools in twenty seconds and returns to its initial position de-energizing the ignition transformer and energizing a main fuel valve 37 through a two-way contact 18 of the power switching relay 15; the contact 18 also prevents re-energization of the thermal relay 20. The contacts 23 operated by the photo-cell to control the ignition transformer may be omitted and in consequence the ignition transformer is not energized until the by-pass fuel valve opens.