780,422. Burner safety control systems. SCULLY SIGNAL CO. Nov. 24, 1953 [Dec. 12, 1952], No. 32556/53. Classes 75(1) and 75(3) In a system for producing and monitoring a flame at a burner 1, Fig. 9, comprising a first electric circuit connecting igniter electrode means with a voltage source 47 to produce an arc to ignite the fuel and a flame monitoring electrode 7 disposed outside the open end of the burner, a second electric circuit is supplied from the source 47 with a voltage of the same magnitude as that supplied to the first circuit and connects the flame monitoring electrode 7 to the first circuit to produce a monitoring current through the flame between the igniter electrode means and the monitoring electrode 7. The igniter electrode means comprises an electrode 5 disposed close to the open end of the burner, the first electric circuit connects the igniter electrode 5 and the burner to the terminals of the voltage source 47 so that an ignition spark passes between the ignition electrode. and the burner. The second electic circuit includes a monitor apparatus 48 and connects the monitoring electrode 7 either, as shown, to the burner or to the igniter electrode 5. In the burner control system shown in Fig., the transformer 47 supplying the voltages to the igniter electrode 5 and the monitoring electrode 7 is energized by a thermostat, aquastat or pressurestat 107 and the moniotring current through the flame of the burner develops a potential across a resistance 49 of one megohm in the grid circuit of a valve 59 in the monitor apparatus 48. This grid potential prevents the valve from conducting and consequently no potential is developed by the valve across a second resistance 69 connected both into the anode circuit of the valve and into the grid circuit of second valve 77. The second valve 77 therefore conducts and energizes a solenoid 81 to close a switch 85 to energize from the mains supply a further solenoid 91 which opens a valve 101 controlling the fuel supply to a main burner (not shown). The thermostat 107 also energizes a solenoid 117 which opens a valve 123 controlling the fuel supply to the pilot burner 1, and a solenoid 105 which closes a time switch 89 in the circuit of the solenoid 91 controlling the fuel valve 101 of main burner. The circuit shown in Fig. 7 provides controls additional to those provided by the circuit of Fig. 6 including provision for rendering the pilot burner flame monitoring circuit inoperative after the elapse of a period of time in which the main burner should have been ignited. Referring to Fig. 7 the solenoid 117 controlling the pilot gas valve 123 and the transformer 47 providing the ignition and monitoring voltages for the pilot burner are de-energized twenty seconds after closure of the thermostat 107 by a switch 115 operated by a solenoid 113, and in order to prevent the main fuel valve 101 from closing in consequence of the de-energization of solenoid 81 by the monitoring apparatus 48 the switch 85 actuated by the solenoid 81 and a safety switch 126 in series with switch 85 and operated by a solenoid 124 controlled by the twenty second delay switch 115 are bypassed by a switch 129 operated by a solenoid 130 energized by a relay circuit 131 actuated by a device such as a photocell 134 responsive to the flame of the main burner. A blower and burner motor starting relay 136 is connected in parallel with the solenoid 105 controlling the main fuel valve 101 and is controlled by a switch 133 actuated by a solenoid 132 energized initially through the series switches 85, 126 and later through the switch 129. The solenoids 105, 113 and 136 are energized at starting by a switch 127 opened by the solenoid 81 and by a switch 128 opened by the solenoid 130 and when the motor starting relay 136 is energized it closes a switch 160 shunting the two switches 127, 128. If the maim burner extinguishes solenoid 130 opens switch 129 and closes the main fuel valve 101 and after a short time for the removal of gases from the boiler the solenoid 132 opens the switch 133 to de-energize the burner motor starting relay 136. The photocell 134 may be replaced by a probe electrode in the flame of the main burner, in which case the probe electrode 7 for the pilot burner is located at the junction of the main and pilot burner flames to serve as the second electrode for a current in the main burner flame. An indicator lamp I lights up when the solenoid 117 for the pilot gas valve is energized. An indicator lamp II lights up when the solenoid 91 for the main gas valve is energized. An indicator lamp III lights up when the switch 85 and the switch 126 or the switch 129 are closed. The pilot burner, Fig. 1, comprises a steel tube 1 extending from a casting forming an inlet 3 for a gas/air mixture and mounted in a hole 28 in the boiler wall 30. The probe electrode 7 and the igniter electrode 5 are disposed within porcelain sleeves 21, 23 supported in a porcelain block 8 clamped to a plate 12 held by screws 27 against the rear wall 14 of the casting. The sleeves pass through openings 10, 18 in the rear wall of the casting and extend through the steel tube 1. The free end of the igniter electrode 5 is U- shaped and terminates just outside a circular opening 2 in an end plate 29 of the steel tube 1. The porcelain sleeve 21 of the probe electrode 7 fits closely within a circular opening 4 formed in the end plate 29 and joined thereto by a slot 6. The free end of the probe electrode 7 is bent downwardly into the flame from the opening 2 and slot 6. The electrode assembly can be withdrawn rearwardly from the tube 1, the downwardly bent part of the probe electrode passing through the slot 6 and through a further slot 24 joining the apertures 10, 18 in the rear wall 14. The gas flow into a mixing chamber 40 leading to the inlet 3 of the burner is adjusted by a valve 42 threaded into a sleeve 36 having an inturned rim 46 for closing gas channels 44 in the valve. The sleeve 36 is adjustably threaded into the inlet end 40<SP>1</SP> of the mixing chamber 40 to vary the flow of air through radial orifices therein (not shown). A nut 34 limits the degree of threading of the valve 42 into the sleeve 36 and a nut 38 limits the degree of threading of the sleeve 36 into the inlet end 40' of the mixing chamber.