GB628189A - Improvements in or relating to safety control systems for fuel burners - Google Patents

Abstract

628,189. Lighting burners. MAY, P. (Robertshaw Thermostat Co.). Jan. 28, 1947, No. 2701. [Classes 75(i) and 75(iii)] A safety control system for a fuel burner of the kind described in Specification 589,873, in which the variation in resistance of a flame sensitive resistor causes variation in the current to a solenoid valve and thus controls the supply of fuel to a burner responsive to the presence or absence of a burner flame, is modified in that the solenoid valve 18 is operated by a control relay 22 instead of being operated directly by a variation of the current therethrough. Current from the secondary of a transformer 30 energized by manual or thermostatic opening of a main fuel valve 14 is supplied to a bridge circuit comprising an arm CD including a resistor 50 located for heating by a pilot burner 24, an arm CB containing the operating coil 42 of a relay 22 adapted to be short-circuited by a switch 56, an arm AB containing a resistor 29, an ignition coil 27, and a switch 58, an arm AD containing a resistor 52, and a detector arm containing a cutout 54. On initial closing of the main switch of valve 14 the relay coil 42 is short circuited by the switch 56 for a short period, of say 5 seconds, during which the ignition coil 27 ignites the pilot burner 24. At the end of said period the switch 56 is opened by the relay coil 60, and the relay coil 42 retracts its core 40 from a spring pressed arm 44 to permit closing of contacts 46, 48 to energize the solenoid valve circuit through a resistor 64 provided with a pilot lamp 62. At the end of a longer period, say 18 seconds, the relay coil 60 opens the switch 58 to de-energise the igniter 27 so that the bridge circuit ceases to exist, and the thermal resistor 50 is connected in parallel with the cutout 54 and the relay coil 42. An alternative system is described in which the fuel supply to the pilot burner 24 is also controlled by the solenoid valve 18 and the latter is energised by the primary of the transformer 30. Specification 594,606 also is referred to.