Patent GB-404989-A (GB)
Title: Improvements in air and draught control systems for furnaces
IPC: F23K3/14
Filed: 1932-07-15
Abstract: 404,989. Regulating air supply and draught in furnaces. IRON FIREMAN MANUFACTURING CO., 984, East 17th Street, and CARTER, H. C., 1424, Reed College Place, both in Portland, Oregon, U.S.A. July 15, 1932, No. 6720/33. Divided on 395,516. [Class 51 (i).] The flow of air for a furnace through an air duct 74 is controlled by means comprising a pilot damper 170 which is moved by a flow of air in the duct and a damper 164 which controls the flow of air, the movements of the control damper being regulated by the pilot damper so that the air flow is maintained constant within narrow limits, and the control damper being moved towards a closed position when delivery of air to the duct ceases. The rate at which the air flow is maintained is controlled by an indicator 176. Air is supplied through the duct by a fan 72 driven by a motor 67. The damper 164, pivoting at 163, is moved by a reversible electric motor 167 through a worm 166 and worm wheel segment 165, which has an arm 168 which opens the switches 169, 169a when the damper reaches its extreme closed and open positions. The shaft 171, on which the flap 170 is carried, rotates in a bear. ing on the duct 74, and carries two cams 172, 173. Rotatably mounted outside the bearing is a casing 175 carrying the pointer 176. Rings 179, 181 of insulating material are attached one to the inside of the casing 175 and the other to the bearing, the cams 172, 173 rotating inside the rings. The ring 179 carries two screw contacts 189, 190 and two spring contacts 183, 184 movable by the cam 173 into contact with the contacts 189, 190 The ring 181 carries two spring contacts 185, 186 movable by the cam 172 into contact with points 191, 192 on the ring 181. The rings also carry rubbing contacts 187, 188. On the ring 179, the rubbing contacts 187, 188 are connected to the spring contacts 183, 184 respectively. On the ring 181, the rubbing contacts 187, 188 are connected to the contact point 191 and spring contact 192 respectively. The power line 97 is connected by a wire 193 to the contact point 192 and the screw contacts 189, 190, by a wire 195 to the rubbing contacts 188, by a wire 196 to the brush 185, and by a wire 194 to the neutral pole of the motor 167. When the fan 72 is stopped and the air flow ceases, the flap 170 drops and the cam 172 closes the contact between the brush 186 and contact point 192, as shown in Fig. 5. Current flows from the power line 97 through the wire 193, contact 192, brush 186, rubbing contact 188, wire 195 to one side of the motor 167, so closing the damper 164. When this damper reaches its closed position the arm 168 opens the switch 169 in the circuit wire 195 and so stops the motor. When air flows again, sufficient passes 'the damper 164 to lift the flap 170, so that the cam 172 releases the brush 186 from the point 192, and brings the brush 185 in contact with the point 191. The brush 183 is still held against the contact screw 189 by the cam 173, as it was when the flap 170 was in its lowest position. Thus current passes through the wire 193, screw 189, brush 183, rubbing contacts 187, contact point 191, brush 185, to the other side of the motor 167, which opens the damper 164, until the cam 173 releases the brush 183 from the screw 189. The position at which this occurs is determined by the position of the screw 189, and this position is controlled by means of the pointer 176. If the air flow decreases, the contact between the brush 183 and screw 189 is renewed and the damper 164 is opened till contact at 183-189 is broken. If the air flow is too great, the cam 173 closes the contact between the brush 184 and screw 190, and current flows through the wire 193, screw 190, brush 184, rubbing contacts 188, and wire 195. If the damper is opened very wide, the arm 168 opens the switch 169a in the wire 196. The furnace is also provided in the flue 145 with a damper 146 controlled by a flap 157 in an air inlet passage 156. The damper 146 is rotated by a reversible electric motor 147 through a worm 148 and worm wheel segment 149. The power line 97 is connected by a wire 161 to the flap 157, which is provided with an arm 158 which can make contact with one of the points 159, 160 when the air flow in the passage 156 is too small or too great. The circuit through the motor is then completed to open or close the damper 146. An arm 151 on the worm wheel segment 149 opens the switch 153 or the switch 154 and stops the motor 147 when the damper 146 reaches its extreme open or closed position.