Patent GB-793477-A (GB)
Title: Improvements in control devices for fluid fuel burners
Inventor: WEBER VICTOR
IPC: F23N5/06
Filed: 1956-02-28
Abstract: 793,477. Thermally-actuated valves. ROBERTSHAW-FULTON CONTROLS CO. Feb. 28, 1956 [July 28, 1955], No. 6194/56. Class 135. A control device for a heating appliance having a fluid fuel burner comprises means setting control valve means 184, Fig. 6, for a first fuel supply rate, means responsive to a temperature to be controlled, means setting the valve means for a lower supply rate upon a temperature change, and means actuating the valve means to terminate the fuel supply upon a further temperature change. In the " off " position of a knob 18, a knob cam 104, Fig. 5, forces in plunger 102 to engage a lever 28, pivoted at 30 on the casing and at 34 on a snap spring 36 connected to a switch arm 38 pivoted at 44, and a portion 100 of lever 28 depresses a cam arm 96 to move a pawl 92 away from an insulated lever 74 pivoted at 78, Fig. 4, and carrying a cross-piece 70 for operating flexible switch arms 56, 56a, so that switches 60, 58 and 59 are open. Pilot valve 170 and main burner valve 184 are closed and knob cam 128, through rod 124, opens switch 108. A knob cam 88 engages a lever 292, Fig. 5, to remove the bias of a spring 289, Fig. 4, on a lever 268, so that a valve 258, Fig. 6, by-passing a main gas restriction 252, is open. Switch 242, Fig. 6, is closed by spring 250 loading lever 232 when a pilot burner diaphragm 220 and thermal element 228 are cold. Rotation of knob 18 to " start," beyond a " high " position, closes switch 108, produces outward movement of diaphragm 20, connected to a thermal bulb 25 within a motordriven drying drum 336, and of lever 28, and snap opening of lever 38 and auxiliary switch 48 for a hot air fan motor 337, Fig. 6. Cam 88 forces in plunger 80 to engage lever 74 with pawl 92 and close switch 58 to drive the fan from electric supply L1, L2, via closed switch 108, wire 344, switch 58 and wires 348, 350, close switch 60 to energize an igniter 342 via transformer 358 through closed switch 240, and close switch 59 for an indicating lamp 364. Cam 88 also moves lever 292 so that spring 290 is compressed and spring 289 loads lever 268 for closing by-pass valve 258, but this is prevented by lever 28 in its cold position, near cover 12, engaging lever 268. Lever 74 moves plungers 216, 208 to compress a spring 206 through a cup 202 which urges valve 184 to open, although valve 184 remains closed under the bias of spring 250; and through lever 210, opens pilot valve 170. The ignited pilot burner heats thermal element 228, 220 to open switch 240, de-energizing the igniter and removes the loading of spring 250 so that spring 206 opens valve 184 and the main burner lights. On releasing knob 18, a spring returns it to " high " position after which it is set for the required drying temperature. At a certain temperature element 20 expands and lever 28 allows spring 289, through lever 268, to close valve 258. Drying continues at a lower rate due to reduced gas flow through orifice 252 and as the set temperature is reached element 20 causes lever 38 to snap over and close the motor holding switch 48. Further expansion of element 20 moves lever 28, 100 to disengage pawl 92 which releases lever 74 to open switches 58, 59, 60 for breaking the first motor and ignition circuits, to release plunger 216 and close valves 184, 170. Closing of pilot valve 170 causes element 220 to contract so that spring 250 loads valve 184 and switch 240 closes. If the drying takes place at a temperature lower than the " high " setting, the operation is the same except cam 88 will not engage lever 292 and valve 258 will remain open. If the drum temperature rises above a safe limit, thermal elements 314, 302 and 316, 304, Fig. 6, expand to move lever 318 and unlatch lever 74 to close both main and pilot valves.