| 摘要 |
In a gas burner control system a normally closed, electromagnetically opened first valve has primary control of gas flow to pilot and main burners and the application of gas pressure to cause a normally closed, diaphragm-operated second valve controlling gas flow to a main burner to open; the first valve opens and a spark igniter becomes operative to ignite the pilot upon closure of a space thermostat. A thermostatically operated switch heated by pilot flame has a cold position through which a circuit to open the first valve is completed and a hot position through which a circuit causing the diaphragm-operated second valve to open is completed. A holding circuit paralleling the switch is effective to hold the first valve open when the switch moves to its hot position, but is ineffective to open it, so that upon failure of the electrical power supply, the first primary control valve will not open until the switch has cooled to its cold position.
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