Patent GB-531301-A (GB)
Title: Improvements in and relating to furnace control
IPC: F23N5/04
Filed: 1939-07-18
Abstract: 531,301. Fluid-pressure servomotors. BRITISH THOMSON-HOUSTON CO., Ltd. July 18, 1939, No. 20796. Convention date, July 20, 1938. [Class 135] A gas furnace is fitted with valve devices for supplying gas at a constant pressure to burners 15, and the flow of gas may be cut off under abnormal conditions such as excess boiler pressure, or low water level, excess furnace or atmospheric temperature, or failure of the pilot burner 16. The control of gas from the inlet pipe 20 to outlet pipe 26 is effected by a valve 30 which is connected to a flexible diaphragm 35 secured by plates 38, 39 and a nut 40 to the valve stem 41 which passes with clearance through a baffle plate 42, so that gas can pass to a chamber 47 below the diaphragm 35 and through the valve stem and aperture 45 to a chamber 46 above the diaphragm. When the pressure in the chambers 46, 47 is equal the valve closes under the action of gravity. The pressure in chamber 46 is controlled by the opening or closing of a valve 50 against its seat 51, the valve being suspended from a pressure responsive diaphragm 57 which is acted on by gas supplied from the outlet chamber 28 via a valve 124 which is open when the water in the boiler is at a sufficiently high level. The gas enters via a clearance in a baffle plate 52 through which the stem of the valve 50 passes, and variations in the pressure of the gas in the outlet chamber 28 cause the valve 50 to assume different positions and thus control the opening of valve 30 and hence the supply of gas is kept at a practically constant pressure. The valve 50 is also under the control of devices which act to stop the gas supply under certain abnormal conditions. The valve is connected to plates 55, 56 by means of a clevis 54 screwed to the valve spindle and an adjustable spring 65 controls the response of the diaphragm 57 to the gas pressure on it. To cut off the gas when the steam pressure is high a diaphragm 70<SP>1</SP> in a chamber 70 connected to the boiler actuates a rod 72 and moves a lever 68 clockwise. This lever actuates a lever 83 with a forked end which engages a washer 85 on the valve rod 86 and closes the valve. The lever 83 is held in raised positition by a magnet 92, and the lever 68 by a spring-pressed arm 88 which acts as a toggle. The parts are returned by a spring 76 but the arm 83 is held by the magnet 92 until the toggle arm snaps into the reversed position when the combined action of the toggle spring and spring 76 overcome the attraction of the magnet and the lever 83 releases the valve rod 86. The rod 86 may also be actuated by a lever 105 upon de-energization of an electromagnet 100 by a thermostat 98 when the room temperature is excessive, or by a pilot flame safety switch 102 which operates when a bimetallic conductor 111 is cooled owing to failure of the pilot jet 16 and permits a spring 112 to open the switch. If the water boiler becomes low a float in chamber 12 operates a valve to stop flow of gas from chamber 61 into the outlet chamber 28. This causes the pressure in chamber 46 to build up and the valve 30 to close. The lever 105 may be operated by a hand lever 130 in emergency upon failure of the electric power for thermostat 98. This lever returns under spring action to normal position when the magnet 100 is energized. The low water float may act direct upon the rod 86. The invention may be applied to controlling a hot water boiler or a warm air furnace. The diaphragm 70<SP>1</SP> is then replaced by a temperature responsive expansible bellows having a temperature responsive bulb in the hot water boiler furnace, or in the air heating chamber of the hot air furnace.