Patent GB-744859-A (GB)
Title: Improvements in control systems for combustion furnaces using fluid or pulverised fuel
Inventor: WILSON WILLIAM HARRY
IPC: F23N5/22
Filed: 1953-08-05
Abstract: 744,859. Controlling burners. RHEOSTATIC CO., Ltd. July 22,1954 [Aug. 5, 1953], No. 21627/53. Class 75(1). A sequence switching device for the safety control of fluid fuel burners comprises a camshaft 20 biassed by a spring 27 to an initial position, and adapted to operate switches 2, 11, 12, 13, 1 in sequence, an electric timing motor 4 driving the camshaft and an electromagnetic clutch 25 connecting the timing motor to the camshaft and energising by contacts in a flame sensitive switch 6 which are closed in the absence of a burner flame, the arrangement being such that the camshaft is rotated from the initial position, Fig. 2, to a ready to start position, Fig. 3, and is held therein, provided a controlling switch 10 is open, by the opening of switch 2 whilst the electromagnetic clutch 25 remains energised. The spring 27 is not strong enough to return the camshaft to the initial position whilst the clutch is energised. In the starting position, Fig. 2, the clutch coil 7 is energised from the mains 8, 9 through the lock out switch 1, a switch 5 and the no-flame contact C of the switch 6, and the timing motor 4 is energised through the lock-out switch 1, contact A of switch 2, and a switch 3. The camshaft therefore rotates until the timing motor is de-energised by a cam 23 breaking the contact A of switch 2. The ready to start position of Fig. 3 is thus established and is held until the controlling switch 10, which is res. ponsive to the temperature of a boiler or room heated by the burner, closes to re-energise the timing motor 4 so that the camshaft rotates further to close the switch 12 for energising an ignition transformer 19 to move the switch 2 to make contact B and to close the switch 11, the switches then having the positions shown in Fig. 4. The camshaft continues to rotate and closes the switch 13 which energises a relay coil 14 operating the switches 3, 5 and a switch 15 energising the motor 17 supplying fuel to the burner and a switch 16 connecting the "flamepresent" contact H of the switch 6 to the relay coil 14, the switches then having the positions shown in Fig. 5. If a flame is established the switch 6 de-energises the clutch coil 7 and the spring 27 returns the cam to the starting position, the cam switches 2, 11, 12, 13 returning to the positions shown in Fig. 2 so that the ignition transformer 19 is de-energised. The relay coil 14 however continues to be energised through the switch 16, the "flame present" contact H of switch 6, switch 5, switch 10 and switch 1 and consequently switch 15 remains closed to supply fuel to the burner. If a flame is not established the clutch coil 7 is not de-energised so that the camshaft continues to rotate until the cam 24 trips the lock-out switch 1 to de-energise the control system and energise an alarm. If the flame fails during a normal run of the burner the switch 6 de-energises the relay coil 14 to shut down the burner supply motor 17 and to return the relay switches 3, 5, 15, 16 to the positions of Fig. 2. The starting sequence is then repeated. In this case of flame failure the controlling switch 10 will be closed in the initial position of Fig. 2 but it is not effective until a purge period has elapsed and the cam 23 breaks the contact A of switch 2. The length of the purge period can be altered by adjusting the cam 23.