Patent GB-606367-A (GB)
Title: Improvements in automatic draught regulators
IPC: F23N3/08
Filed: 1946-01-12
Abstract: 606,367. Furnaces. LAMBRETTE, J. J. Jan. 12, 1946, No. 1167. Convention date, Feb. 9, 1940. [Class 51(i)] A furnace wherein automatic draughtregulating means operate to close the damper progressively as combustion proceeds, until the minimum opening position of the damper is reached, thus allowing the firedoor, or doors, to be opened, the damper being fully opened when the door, or doors, are again closed after re-fuelling, is characterized by the automatic dampercontrol being effected by electro-mechanical devices which are substantially enclosed to prevent access thereto by the stoker. As shown, the damper 7 and counter-weight 8 are supported by cables 6, 9 trained over a pulley 5, the tendency being for the unbalanced weights to close the damper 7. The damper is opened by a motor 21 which is geared to the shaft 3 carrying the pulley 5, the driving-connection incorporating a clutch 24 which may slip if the damper movement is obstructed. Adjustable stops 12, 15 on the shaft 3 determine the maximum and minimum extents of damper opening, the abutment 16 being removable from the path of the stop 15, by a lever 19, to permit the damper to close completely. In operation, the. damper is fully opened by the motor 21 when the fire door, or doors, 99, are closed. The shaft 4, driven from the shaft 3 by means 10, carries cams 57. 58, 59 which control the inclinations of levers 66, 67, 68 on which mercury switches 71, 72, 73 are carried. The shaft 4 is fast with a disc 25 having ratchet teeth which are engageable by a roller 30 on a rod 29 carried by a pivoted saddle 27. Springs 31 tend to keep the roller 30 in engagement with the teeth and thus prevent the closing movement of the damper. The roller 30 is removable from the disc 25 either by means actuated by an electro-magnet 34 or by an electromagnet 39a, the said means comprising levers 33, 36 having cam-like ends which, on excitation of the electro-magnets, engage under the bar 29 and move it from the disc 25. The electro-magnet 34 is in series with a mercury switch 104 which completes the circuit only when a door 99 is opened, so that during normal combustion with the doors closed, the damper is under the automatic control of the magnet 39a. When the magnet 39a is excited, the end 40 of the lever 36 swings a lever 41 about its pivot 42 and thus raises a vertically slidable rod 43 having a roller end 45 which raises the arm 46 of a fluid dashpot 47. The arm 46 is movable upwards freely, but the return motion is by gravity at a speed controlled by the dashpot. On upward motion of the arm 46, an adjustable stop 51 on a curved rod 50 tilts a lever 48 carrying a mercury switch 39 in the circuit of the magnet 39a, This breaks the circuit and the magnet releases the lever 36 and allows the roller 30 to engage the teeth of the disc 25 thereby stopping the closing of the damper. The downward movement of the arm 46 allows the lever 48 to swing back and restore the switch 39 to its closed position, so that the magnet 39a is again excited .and the roller 30 is again withdrawn from the disc 25, to permit a predetermined movement of the disc 25 and damper 7 before the closing of the latter is again stopped. The intermittent closing continues until the damper approaches its minimum extent of opening, when the cam 59 operates the switch 73 to break the circuit of the magnet 39a and the roller 30 finally arrests the damper. When the door 99 is opened, the link carrying the switch 104 is tilted by linkage 97, 98 to close the switch 104, the switch 71 having been closed by rotation of the cam 57. This excites the magnet 34 and disengages the roller 30 from the disc 25 to permit the damper to close to the extent permitted by the stops 15, 16. The opening of the door 99 likewise opens a switch 105 in the motor circuit, another switch 83a being closed, during the final closing movement of the damper by a pivoted spring-controlled finger 77 on an arm 75 on the shaft 4 engaging a crank pin 81 on the switch-carrying shaft 83. This prepares the motor circuit for immediate operation of the motor on closure of the switch 105 which occurs when the door 99 is closed. The arm 85 opens the switch 83a when the damper is fully opened. The switch 72 operated by the cam 58 operates a pilot light 74 to indicate to the stoker that the damper 7 is near its minimum opening the position of the damper being shown by a pointer 88 actuated by a cable running over pulleys 91, 90 and attached to the damper and a counterweight 92. The stoker may close the damper by moving the lever 35 to pivot the lever 33 to remove the roller 30 from the ratchet teeth. A main switch 106 and tell-tale lamp 107 are provided. If desired, an adjustable crank 107<1> may be fitted to the end of the shaft 3 to operate a valve 110 controlling the injection of steam or additional air to the furnace for a limited time after recharging the furnace and closing the door.