Patent GB-639832-A (GB)
Title: Improvements in or relating to means for the automatic control of steam boiler auxiliaries
IPC: F23N1/00
Filed: 1947-01-06
Abstract: 639,832. Automatic pressure control systems. ELECTROFLO METERS CO., Ltd., and GEMMELL, D. C. N. Jan. 6, 1947, No. 418. [Class 38 (iv)] [Also in Group XXIX] In apparatus for maintaining constant the steam pressure of boilers through the medium of auxiliaries, such as draught fans and fuel conveyers, the auxiliaries are driven by electric motors, the voltage and speed of which are regulated in accordance with the steam demand through the intermediary of a pneumatic or hydraulic regulator wherein a value corresponding to the steam pressure is balanced by a value variable in accordance with the motor voltage and speed. Fig. 3 shows the regulator which comprises a diaphragm 32 responsive to air pressure delivered from relay apparatus, Fig. 2, by a pipe 22, and variable with the pressure of steam in the pipe 11, Fig. 2. The diaphragm 32 controls a bleed valve 39 in the hydraulic circuit of a servomotor 50, the arrangement being such that operation of the valve 39 varies the pressure beneath a piston 43 which operates through a pivoted lever 45 slide valves 47, 48 to admit high or low pressure fluid to the servomotor 50. Operation of the servomotor tends to reset the pivoted lever 45 through the links 52, 53 and the slide valves 47, 48 are restored to normal position when the system is rebalanced. The servomotor 50 operates a phase-shifter in the grid circuit of a mercury-arc rectifier to vary the voltage applied to the motors driving the boiler auxiliaries and rebalance is effected when the steam pressure is restored to the predetermined level. This rebalance is brought about by an auxiliary motor 54 having the same voltage/speed characteristic as the main motors and operating to restore to normal position a lever 33 connected to the diaphragm 32. The lever 33 is operated by the motor 54 through a fluid drive comprising a chamber 55 having radial fins 56, 57 which impart rotary motion to oil within the chamber so as to exert a force on a member 58 suspended from the lever 33. The piston 43 is associated with the diaphragm 32 through a dash-pot 110, 111 to damp movements of the piston and pivoted lever 45. The relay apparatus, Fig. 2, which is responsive to steam pressure of the boiler through pipe 11, comprises a spring-controlled diaphragm 12 adapted to operate a pivoted lever 14 associated with the cup valve 16 of an auxiliary compressed air supply 27. When the steam pressure varies, the cup valve 16 adjusts the air pressure to a value corresponding to the new steam pressure, stable conditions being obtained through the intermediary of the air pressure diaphragm 17. The air pressure developed by the cup-valve 16 is transmitted to the chamber 19 and thence by pipes 22, 23 to regulating apparatus such as that shown in Fig. 3. A change-over valve 84 is provided so that the air pressure in the chamber 19 may be regulated manually by a system 24, 25, 26. The motor 54 and fluid drive 55, Fig. 3, may be replaced by a solenoid, Fig. 4 (not shown), operated by the variable voltage and located in the field of an energized or permanent magnet. Specification 491,459, [Group XXIX], is referred to.