Patent GB-790623-A (GB)
Title: Improvements in or relating to control devices for fluid pressure systems
Inventor: DIMMOCK NORMAN ALBERT
IPC: F04D27/02
Filed: 1954-02-03
Abstract: 790,623. Axial-flow compressors. POWER JETS (RESEARCH & DEVELOPMENT), Ltd. Feb. 3, 1955 [Feb. 3, 1954], No. 3200/54. Class 110 (1). [Also in Groups XXIX and XXXVII] An automatic control device 7 associated with a fluid system supplied by a dynamic compressor 1 comprises actuating means such as the flexible diaphragm 12, responsive to a change in the fluid pressure at a point in the system which might lead to surging of the compressor, for actuating quick-acting auxiliary protective means, such as the auxiliary blow-off valve 8, for delaying surging of the compressor, timing means for terminating the operation of the actuating means after a time regardless of whether the pressure at the point has returned to its original value or has assumed a different value, and with re-setting means for subsequently automatically re-setting the device so that the actuating means will respond to a further change in pressure in the system. The compressor 1 supplies a consuming means 3 which may be some combustion apparatus through a duct 2 and has a main blow-off valve 5 controlled by a controller 6 responsive to the fluid pressure and flow upstream of the branch 4 containing the blow valve 5. The device 7 is quicker acting than the normal controller 6 and is responsive to the pressure at a point near the consumer 3 to control the auxiliary blow-off valve 8. The device 7, Fig. 2, comprises a casing divided into two chambers 10, 11 by the diaphragm 12. The chamber 10 is connected to the duct 2 through a hollow neck 13 and a non- return valve 14. The chambers 10, 11 are connected to one another by a restricted passage 18 adjustable by a needle or similar valve 19. A contact 24 on the diaphragm engages an adjustably fixed and insulated contact 26 when the pressure in the chamber 10 temporarily exceeds that in the chamber 11 and so initiates a control operation. Such operation ceases when the pressures in the chambers 10, 11 are equalized by the leak 15. A further adjustable leak 23 bypasses the non-return valve 14 so that the pressure in both chambers 10, 11 eventually equalizes with that in the duct 2. The control device is then re-set and ready to respond to a further change of pressure. A second non-return valve may be provided in the leakage path 21, 20 to prevent leakage into the chamber 10. The leak 23 then operates to re-set the control device only on a fall of pressure in the duct. The protective device may alternatively be rendered operative by the opening of the contacts 24, 25 which are then arranged to be normally closed. In Fig. 1 the contacts 24, 25 when closed energize a relay 29 which in turn energizes a solenoid 31. The solenoid 31 actuates a spring-loaded piston valve 32 controlling a servo-piston 36 which operates the auxiliary blow-off valve 8. When the solenoid is energized, the lower side of the piston 36 has an unrestricted connection with atmosphere and the pressure supply to the upper side of the piston 36 is no longer restricted. The full supply pressure aided by the store in a reservoir 41 quickly opens the valve 8. Its closing movement, however, is retarded since the supply to the under side of the piston 36 is through the restriction 45 when the solenoid 31 is deenergized.