Patent GB-942650-A (GB)
Title: Control device for fuel-burning apparatus
IPC: F23N1/00
Filed: 1962-07-19
Abstract: 942,650. Valves. ROBERTSHAW-FULTON CONTROLS CO. July 19, 1962 [July 19, 1961], No. 27860/62. Heading F2V. [Also in Division F4] A control device for a gas burning apparatus, for instance a cooking oven, 30, Fig. 1, comprises a pilot burner 54 fed with gas by two passages, one of which includes a valve 76, Fig. 7, actuated by a thermostat 56 responsive to the oven temperature, and a main burner 36 supplied with gas through a valve 58 opened by a thermostat 57 responsive to an enlarged flame of the pilot burner. When the temperature of the oven reaches a value set by the manipulator 42 of a thermostat unit 40, the pilot valve 76 closes and the pilot burner is supplied through one passage only to provide a small flame which is unable to heat the thermostat 57 for the main valve 58, and consequently the main burner 36 goes out. The combined supply of gas to the pilot burner is also controlled by an electromagnetic safety valve 59 held in open position against the action of a spring by the current developed in a thermocouple 60 heated by the small flame of the pilot burner. At starting the safety valve 59 is held open by means of a push-button 65 until the thermocouple becomes heated. The thermostat unit 40 includes a filter for the pilot gas and two adjusting pins for regulating the flows of gas through the two pilot passages. The oven thermostat 56 contains a gas or a liquid and is connected by a tube 66 to a diaphragm or bellows 68, Fig. 7, adapted to rock an arm 70 about a fulcrum point 72 on the end of a fulcrum pin 182 axially adjusted by means of the manipulator 42. The arm pushes against a plunger 74 to open the pilot valve 76 against the action of a spring 78. The manipulator 42 is slidably keyed to a threaded sleeve 170 screwed into the body of the thermostat unit and a calibrating screw 180 is screwed into the threaded sleeve 170 to abut the lower end of the fulcrum pin 182. The latter is held down against the calibrating screw 180 by a spring 232. The fulcrum pin is coupled to the threaded sleeve 170, so as to be turned therewith, by pins 188 on the fulcrum pin engaging longitudinal slots in the sleeve 170, and a rounded lip 192 on the fulcrum pin is adapted to engage a lifting cam on the body of the thermostat unit as the manipulator 42 is being turned toward the off position. In consequence the fulcrum is quickly raised and finally slides over a hump on the cam into a locking groove. The fulcrum pin can also be raised by the action of an electric heater 116 adapted to be energized by a timer 86, Fig. 1, at the end of a timed cooling period whereby the oven is then maintained at a lower temperature than that which was maintained during the cooking period. The heater 116 heats a double walled diaphragm 218 containing water and the upper web of the diaphragm is welded to a ball which engages a lever 118 having a forked end 232 straddling the fulcrum pin 182. The upward movement of the lever 118 is limited by an adjustable pin 124 threaded into a sleeve 228 threaded into the body of the unit. The height of the pin is adjusted by turning the sleeve 228 with a screw driver, the external threads of the sleeve being of greater pitch than its internal threads. Rotation of the pin is prevented by making it rectangular at 124A. The height of the diaphragm can be adjusted by a screw 224. A spring 236 holds the lever 118 down. A multiple pole switch 240 is operated by an extension of the fulcrum pin 182 so that when the manipulator 42 is at an on-position contacts 246 and 248, Fig. 1, are closed and contact 250 is open and when the manipulator is at the offposition contacts 246 and 248 are open and contact 250 closed. Another switch 264 is operated by an extension from the top of the rocking arm 70 and comprises a relatively stiff blade disposed between two bendable blades carrying contacts 260, 262. When the oven is above the set temperature the stiff blade moves upward to break the contacts 260, 262 and when the oven is below the set temperature the stiff blade moves downwardly to break the contacts 260, 262. The contacts 260, 262 close when the pilot valve 76 has contacted its seat because the oven is near the set temperature. The oven may also be controlled by a timer 86 actuated by an electric motor 112 and adapted to actuate three switches 92, 94, 96. The timer is set by a handle 88. The switch 96 is closed at all handle positions except at the off-position 90. The switch 94 is in an up-position to close two contacts 318, 320 and 322, 324 and to open a third contact 314, 316 when the handle is in the zone between positions 108 and 90. The switch 92 is in a closed position when the handle is in a zone 106. If the timer handle 88 is positioned between the positions 90 and 108 and the manipulator 42 of the thermostat set to a desired temperature a light 100 is illuminated continuously and a light 98 is illuminated intermittently by the switch 264 as the oven temperature passes up and down past the selected temperature. The timer motor is not, however, energized so that the timer does not interfere with the heating operation. If it is desired to cook at a predetermined temperature for a predetermined time the handle 88 is first set between positions 90 and 108 and the manipulator 42 turned to the desired temperature. When the light 98 begins to illuminate intermittently the food to be cooked is put into the oven. At the same time the timer is turned to the cooking time required. The timer motor is now energized, the intermittent light 98 is de-energized and a further light 110 is continuously illuminated to indicate that the oven is being controlled by the timer. When the handle 88 is passing over the zone 106 switch 92 closes to cause a buzzer 104 to sound for fifteen seconds. When the handle 88 reaches the position 108 contacts 314, 316 of switch 94 open to stop the motor 112. The light 98 and the buzzer 104 are then energized intermittently by the switch 264. The electric heater 116 is now energized by the closed contacts 310, 312 of switch 96 and the closed contacts 322, 324 of switch 94 and causes the lever 118 to raise the fulcrum 72 of the thermostat unit, and consequently the burner is controlled to maintain a lower temperature in the oven. When the user turns the manipulator 42 to the off position the timer motor 112 is again energized and drives the handle 88 to the off position 90. The manipulator 42 may be returned to the off position by a motor energized by a circuit corresponding to the circuit of the electric heater 116. A two-way switch may be provided for selecting either the electric heater or the manipulator return motor. The timer 86, Fig. 25, comprises a cam 450 actuating a roller 454 and a bell-crank 456, 458 pivoted at 460. The movement of the bellcrank is transmitted to the three switches 92, 94, 96 by a pusher 464. The electric motor is coupled to the shaft of the cam by gear-wheels and by a slip clutch which enables the cam to be rotated manually without rotating ' the motor.