Fuel supply and ignition control system employing flame sensing via spark electrodes

In a fuel supply and ignition system including a pilot valve operable to supply fuel to a pilot outlet for ignition;

• spark generating means including electrode means located in the proximity of the pilot outlet defining a spark gap, and means for activating the electrodes to generate sparks for igniting the pilot fuel to provide a pilot flame which bridges the spark gap;
• and a main valve operable to supply fuel to a main burner for ignition by the pilot flame;
• a control circuit comprising:
• activate means for energizing said pilot valve;
• first switching means operable when enabled to energize said main valve;
• second switching means having first and second control inputs and an output coupled to said first switching means;
• first circuit means for providing a reference signal at said first control input of said second switching means for preventing the enabling of said second switching means in the absence of a pilot flame;
• second circuit means including a capacitor which provides a signal at said second control input of said second switching means;
• a flame sensing network connected in circuit with said spark electrode means for providing a flame signal whenever a pilot flame bridges the spark gap;
• and a charge control circuit means including a controllable switching device for controlling the charging of the capacitor, said controllable switching device being operable in the absence of said flame signal to limit the charging of said capacitor whereby said second switching means is maintained disabled in the absence of a flame, and said controllable switching device being responsive to said flame signal to permit said capacitor to charge to a value which provides a signal at said second control input which enables said second switching means to provide a signal at its output which enables said first switching means.

In a fuel supply and ignition system including a pilot valve actuated by a pilot valve solenoid to supply fuel to a pilot outlet for ignition;

• spark generating means including spark electrode means located in the proximity of the pilot outlet defining a spark gap, and means for activating said spark electrode means to generate sparks for igniting the pilot fuel to provide a pilot flame which bridges the spark gap;
• and a main valve actuated by a main valve solenoid to supply fuel to a main burner for ignition by the pilot flame;
• a control circuit comprising:
• enabling means operable in the absence of a flame at said pilot outlet to generate enabling signals;
• switching means for controlling the energization of said pilot and main valve solenoids;
• activate means for enabling said switching means to respond to said enabling signals to operate and provide an energizing path for said pilot valve solenoid to operate said pilot valve;
• a flame sensing network connected in circuit with said spark electrode means for providing an inhibit signal when a flame bridges the spark gap, and means for coupling said inhibit signal to said enabling means to inhibit the generation of further enabling signals, causing said switching means to be disabled, and said energizing path for said pilot valve solenoid being interrupted when said switching means is disabled, permitting said main valve solenoid to actuate said main valve, said pilot valve solenoid being maintained energized over a holding circuit path including said main valve solenoid after said switching means is disabled.