594,605. Safety controls for fuel burners. MAY, P. (Robertshaw Thermostat Co.). May 17, 1945. No. 12427. [Classes 75 (i) and 75 (iii)] [Also in Group XXIX] A safety control device for fuel burners comprises a bridge circuit in one arm of which is an igniter 40 and a delayed opening switch 42, in another arm a fuel control valve 16, and in the other two arms ballast resistors 58, 66, the current supplied to maintain the valve 16 open being insufficient after the switch 42 has opened unless the ballast resistor 58 is heated. Opening of the main fuel valve closes a switch 14 to allow current to pass from a transformer secondary 24 to the electromagnetic valve 16 to open this valve to allow fuel to pass to the burner component, and to allow current to pass to an igniter 40 to light a pilot burner if there is one, or to light the main burner directly. When the delayed opening switch 42 opens, the igniter 40 is disconnected, and the current flowing through valve 16 and cut-out 70 is not sufficient to maintain the valve in its open position unless the resistance of the shunt 58 has been increased sufficiently due to its being heated by the pilot burner or main burner. The cut-out 70 is adapted to operate on an increase of current due to a failure in the resistor 58. Specifications 572,130 and 589,873, and U.S.A. Specifications 1,778,439 and 2,224,873 are referred to.