Patent GB-1401795-A (GB)
Title: Fuel combustion control devices
IPC: F23N5/02
Filed: 1972-07-13
Abstract: 1401795 Automatic control of temperature MATSUSHITA ELECTRIC INDSUTRIAL CO Ltd 13 July 1972 [6 Oct 1971 (2)] 32759/72 Heading G3R [Also in Divisions F2 and F4] A device for controlling fuel flow to a burner for heating a medium has an electromagnetically operable valve 8, Fig. 2, for supplying fuel to the burner at a continuously variable flow-rate dependent upon the degree of energization of the valve, temperature sensing control means X, Fig. 8, responsive to the temperature of said medium to control valve energization in a sense to maintain the medium at a set predetermined temperature, and second control means 1 responsive to the degree of valve energization falling below a predetermined value to change the setting of the temperature sensing control means in a sense to reduce the set predetermined temperature whereby to temporarily cut off fuel supply to the burner, thereby preventing lighting back at low flow-rates. The control device is applicable to gas or other fuels and to gas furnaces. As applied to a hot water heater, Fig. 1 (not shown), a thermistor 30, Fig. 8, is located in a hot water pipe (1), through which water is pushed by a pump (4) to a radiator, said water being heated by a heat-exchanger (3), and the valve 8 controlling fuel gas flow into a burner assembly (2) heating the heat exchanger (3). An output transistor 55 of a bridge circuit X is operative to affect the conduction of a transistor 56 supplying current to solenoid 9 of the valve 8 and an output transistor 63 of a circuit Y affects the bridge balance and thereby acts on transistor 56. On first switching on valve 8 is fully opened and maximum fuel flow occurs until the water heats thermistor 30 to begin closing the valve until the water reaches the set predetermined temperature and the valve is opened to an extent dependent on the heat load. The set predetermined temperature can be adjusted by a potentiometer 52. If the heat load subsequently decreases the current to solenoid 9 is also decreased until it reaches said predetermined value whereat the valve 8 is abruptly closed. The water temperature therefore drops and the valve 8 is subsequently opened, such opening being initially gradual to slowly increase the gas flow-rate while re-ignition occurs but thereafter being abrupt so that maximum gas flow occurs whereafter the valve opening is dependent on the heat load or above. THE SOLENOID VALVE 8, Fig. 2 comprises an operating coil 9 on a bobbin 10 and a plunger 14 carrying a valve member 27 engageable against a valve seat 26. The plunger is supported clear of contact with bobbin 10 by pivot pins 14a, 14b supported by the ends of the legs of U-shaped leaf-springs 17, 17a. An alternative suspension giving rise to no lateral movement of plunger 14 relative to bobbin 10 comprises rectangular frameshaped leaf-springs fixed at one end with the plunger extending through the central aperture, the other end of each such spring being attached to the base of a respective U-shaped spring, the plunger being supported by the legs of said U- shaped springs, Fig. 6, 7 (not shown).