Patent GB-1058587-A (GB)
Title: Thermostatic control device for a fuel burner
IPC: F23N5/02
Filed: 1963-10-28
Abstract: 1,058,587. Fluid-pressure servomotor systems. ROBERTSHAW CONTROLS CO. Oct. 28, 1963 [Jan. 18, 1963], No.42477/63. Heading G3P. In a thermostatic control device for a gaseous fuel burner a diaphragm 38 controlling the gas flow from an inlet 18 to an outlet 20 is actuated by variations of pressure in a chamber 40 controlled by valves 136, 170, 174. To light the burner a rotary valve 28 is turned by a knob 30 to a position for supplying a pilot burner through a passage 56, filter cavity 58, passage 60, pilot valve 66 and passage 62. The pilot valve is normally closed but opens in response to depression of the knob 30 which, through a knob 104, pivots a lever 92 about a fulcrum 98 to allow a spring 150 to open the pilot valve. When the pilot burner has been ignited a thermocouple energizes an electromagnet 74 to hold the left-hand end of the lever 92 so that the knob 30 can be released to allow the right-hand end of the lever 92 to move upwardly and permit further opening of the pilot valve and opening of the valve 136. If the rotary valve 28 is now turned to the full-on position gas can pass to a chamber 42 and through a passage 158, filter cavity 160 and passages 162, 166 to a chamber 40 behind the diaphragm 38 to hold the main gas valve 50 closed. The valve 50 opens on reduction of pressure in the chamber 40 due to opening of the valve 170 which allows gas to escape from the passage 166 through a passage 154, valve 136, passage 156, valve 174 and passage 176. The valve 170 is opened through snap-acting mechanism 276 and a lever 200 pivoted at 210 when the temperature sensed by a bulb situated in the space to be heated, e.g. a room or a water tank, and connected to a bellows 186, is below the value set by a knob 34. Alternatively, the valve 170 may be electromagnetically operated by a thermostatic switch. The degree of opening of the main gas valve is then determined by the valve 174 which is opened by pressure of a spring 226, adjusted by the bellows 186 and lever 200, in opposition to the pressure in the passage 176 acting on a diaphragm assembly 220, 222. The effective area of the diaphragm assembly is adjusted for high pressure petroleum gas or low pressure natural gas by a plunger valve 252. Excessive temperature, causing snap closure of the valve 170, or extinguishing of the pilot flame, causing closure of the valve 136, results in closure of the main valve. The valve 170 can be overridden manually in the opening sense by the lifting of a plunger 302. In a modification, a water tank heated by the main burner has in its upper and lower parts temperature responsive valves connected in series with other and with an additional, intermittent pilot burner arranged to heat a mercury filled bulb communicating with a bellows for actuating the valve 170. The snap-acting mechanism is dispensed with, and the valve 170 is opened rapidly by vaporization of the mercury in response to flame at the intermittent pilot burner, which is ignited by the continuous pilot burner when both temperature responsive valves are open, indicating a demand for heat. In a further modification the electromagnet 74 is omitted, the valves 64, 136 are actuated by a mercury filled bellows connected with a bulb heated by the pilot burner, the loading spring of the valve 174 is subject to manual instead of thermal adjustment, and in place of the valve 170 a pair of valves in series and responsive to temperatures in the upper and lower parts of a water tank heated by the main burner are provided. Alternatively, an electromagnetically operated, temperature responsive valve may be used instead of the pair of valves in series.