Patent GB-371002-A (GB)
Title: Means for automatically controlling oil, gas or powdered fuel fired furnaces
IPC: F23N1/00
Filed: 1930-11-12
Abstract: 371,002. Electrically-actuated valves. SATCHWELL, L., Farnham Road, Slough, Buckinghamshire. Nov. 12, 1930, Nos. 34047/30 and 4123/31. [Class 135.] The increase in resistance due to the heat generated by the passage of an electric current through a resistance is utilized to afford definite time delay between the completion and breakage of the circuit to an electric motor 10 or, according to the Provisional Specifications, a valve supplying liquid, gaseous, or powdered fuel to a furnace should ignition not occur. In Fig. 1, a thermostat 17 on a fall in the room temperature completes the circuit through an electromagnet 16 and thereby closes a switch 13 against the resistance of a spring 14 to supply current to the electric motor 10 from the mains 11, 12. The operation of the switch 13 removes a catch 19 from the position in which it holds closed a switch 18 in the circuit of the electromagnet 16. The switch 18 is urged upwards by a spring 20 but immediately after the closing of the switch 13 is prevented from rising by the current passing through a relay coil 21 and a resistance 22. As the resistance 22 becomes heated its value increases and the current through the coil will become insufficient to overcome the action of the spring 20 unless ignition of the fuel occurs when the heat of the flame closes a thermal switch 26 to complete the circuit to a fixed resistance 25 in parallel with the resistance 22, thus causing additional current to pass through the coil 21. The opening of the switch 18 completes the circuit to an indicating device 27. The catch 19 is made in two pivoted parts so that the switch 18 may be reset without closing the switch 13 by pressing a button 28. In a modification the electromagnet 16, the switch 18, and the relay coils for operating the switch 18 are supplied with current from the step-down transformer, the primary coil of which is in series with the thermostat 17 across the mains 11, 12. In another modification a relay coil tending to open the switch 18 is substituted for the spring 20. In a further modification a relay coil tending to open the switch 18 and a resistance which is not appreciably affected by the passage of the current passing through it but is subjected to the heat of the furnace flame are arranged in parallel with a relay coil tending to hold the switch 18 closed and a resistance which will rise in value on the passage of the current. In Fig. 5 a resistance 52 varying in value on the passage of a current is arranged in series with an invariable resistance 53 across the mains 11, 12, a relay coil 40 tending to open the switch 18 being shunted across the resistance 52 and a relay coil 41 tending to hold the switch 18 closed being shunted in series with the thermal switch 26 subjected to the heat of the furnace flame across the resistance 53. The potential drop across the resistance 52 is initially insufficient to operate the switch 18 but it will become sufficient as the temperature of the resistance increases unless the circuit of the coil 41 is closed by the switch 26. In another modification the relay switch 18 is arranged in the main circuit before the switch 13. The circuit to the ignition coil may be closed by the main switch, a thermal switch arranged in the ignition circuit opening when heated by the resistance 22. Fig. 8 shows a modification of the circuit shown in Fig. 1 in which the operation of the main switch 13 on the closing of the room thermostat 17 actuates a rocking arm to close and then release a switch 71. The ignition coil 68 and a circuit including a relay coil 74 holding closed the switch 71, a relay coil 73 holding closed the switch 18, and a .resistance 75 similar to the resistance 22 are connected in parallel with the coil of the electromagnet 16. After a certain time the heating of the resistance 75 reduces the current flowing through the coils 74, 73 so that the switch 71 will be opened by its spring 78, and the switch 18 will also be opened by its spring 20 unless the burner has been ignited when the heat of the flame closes a thermal switch 26 to complete the circuit through a second holding coil 76.