Patent GB-624359-A (GB)
Title: Improvements in or relating to control and ignition systems for fluid fuel burners
IPC: F23N5/10
Filed: 1946-02-13
Abstract: 624,359. Fluid fuel burners. ELLIS, L. S. E. (Robertshaw Thermostat Co.). Feb. 13, 1946, No. 4496. [Classes 75(i) and 75(iii)] [Also in Group XXXV] The Fig. shows an electric control system for a fluid fuel burner, wherein the flow to burner 10 is controlled by stopcock 14 and by a manual-set automatic-reset electromagnetic valve 16 of known type biased normally to closed position. A pilot burner 22 is fed from the fuel line intermediately between cock 14 and valve 16, which is operated by armature 25 attracted by coil 24, which is energised with A.C. from mains 80 through transformer 82, contacts 38 and 52, and a known device 62 sensitive to a condition (for example temperature) dependent on operation of the main burner. A bimetallic spiral thermostat 64 exposed to temperature of a space heated by burner 10 carries contacts 70, 68 successively engaging contacts 74, 72 on a drop in temperature and disengaging them on a rise. A heater coil 76 for the thermostat is connected in series therewith and with contact 102 engaged by the armature 25 of the electromagnetic valve, and is short circuited on closure of contacts 68, 72. An electromagnetic switch 26 has an armature 30 movable, by a reciprocable stem 32, having lost motion connection therewith, between attracted and released positions relative to a magnet 28 whose winding 60 is energised by a thermocouple 54 exposed to the pilot burner heat. The stem is biased upwards by spring 34 tending to open contacts 38, 40 while head 36 is depressible by a movement of pivoted lever 50 (which simultaneously opens contacts 52) as a result of the magnetic attraction of plunger 44, (to which the lever is linked), by the primary of transformer 106 supplying the pilot burner ignition coil 128. This transformer is supplied from the mains through normally closed thermally operated snap switch 108, which is opened by heating coil 122 energised through contact 40. When the system is turned on, fuel flows to the pilot burner 22, and the primary of transformer 106 is energised from the mains through thermal switch 108, attracting plunger 44, and heating the coil 128 to ignite the fuel at the pilot burner. Lever 50 opens contacts 52 and presses down stem 32 to close contacts 38, 40 and bring armature 30 into engagement with the magnet poles against the spring bias. Heater 122 is energised and after a predetermined time opens switch 108, de-energising coil 128 and releasing plunger 44 so that contacts 52 close and stem 32 tends to press armature 30 away from the magnet poles. Thermocouple 54 is now hot, and energises winding 60 sufficiently to hold armature 30 to the magnet poles, and coil 24 is energised, provided that the space thermostat 64 has closed contacts 68, 72, 70, 74. Valve 16 opens and fuel is supplied to burner 10. When a required space temperature has been reached contacts 68, 72 first open and the heat developed in heater coil 76 accelerates the opening of contacts 68, 72 to de-energise coil 24 and close valve 16. If the pilot burner is extinguished, thermocouple 54 cools, so that the attraction of the magnet becomes insufficient to hold armature 30 against spring 34, so that contacts 38, 40 open to cut off fuel from the main burner and to de-energise the heater coil 122 of switch 108. After a time interval for cooling the switch closes and the burner may be restarted as described above. On a power failure, valve 16 may be operated manually until on resumption of power supply it is automatically reset to operate under thermostatic control without interruption of fuel flow. Specification 601,739 is referred to.