GB650346A - Improvements in or relating to control apparatus for electrode boilers or water heaters - Google Patents

Abstract

650,346. Automatic current control systems. BASTIAN & ALLEN, Ltd., and COX, W. J. G. Aug. 3, 1948, No. 20485. [Class 38 (iv)] [Also in Group XXXVIII] In a boiler or water heater the current supply to the electrode is maintained at a value which depends on, and is variable with, a second quantity, e.g. the temperature or pressure in the boiler. As shown, a boiler 10, having electrode 11, connected to a threephase supply, is supplied with water from a tank 14 by means of pump 15 operated by a motor 16. A feed-back path is provided comprising a pipe 17 and electrically-operated blow-off valve 18. Regulation of the current supply is achieved by a current transformer 24, coupled to one of the supply lines, which operates a relay 23 when the current to the boiler exceeds a predetermined value. Operation of relay 23 energizes the blow-off valve 18, thereby allowing the pressure in the boiler to force water back into the tank 14, thus reducing contact area between the water and the electrode and consequently reducing the current. The current value at which the relay 23 operates is varied in accordance with the pressure in the boiler. A pipe 26 connected to the boiler allows the pressure to actuate bellows 25, having a push-rod 29 which turns a rod 30 about a pivot 30a. A bar 32 containing a plurality of mercury switches 35 and pivoted at 33 is actuated by the rod 30 and push-rod 31 in such a manner that as pressure in the boiler increases the bar 32 is turned in a clockwise direction. Connected across the mercury switches are resistors 36 which are connected in parallel with the relay 23 across the transformer 24, and these resistors are successively put in circuit as the bar 32 is tilted, thereby causing a greater proportion of current to flow in the relay 23, and thus lowering the current value at which the relay operates as the pressure in the boiler increases. If, when the bar 32 is tilted to its furthest position and the water level in the boiler still rises, a screw 40 on the rod 30 is adapted to actuate mercury switches 43, 44. Switch 43 serves to disconnect the motor 16 from the supply, and switch 44 causing the relay 23 to become energized so that excess water is blown back into the tank 14. The apparatus may be operated in accordance with temperature instead of pressure variations.