GB648316A - Improvements in or relating to pump control systems - Google Patents

Abstract

648,316. Centrifugal and axial-flow pumps &c. ELECTROFLO METERS CO., Ltd. Aug. 8, 1947, No. 21829. Convention date, Sept. 25, 1944. [Class 110(i)] [Also in Group XXIX] Surging in a pump is prevented by a control system comprising a blow-off valve situated in the discharge conduit of the pump and regulated by means comprising a balance beam urged in one direction by means responsive to a pressure which is a function of the flow through the pump and in the opposite direction by means of a pressure which is a function of the pressure in the discharge conduit or of a pressure which is set to control the pressure in the discharge conduit, a governor for controlling the pump speed, means for creating a loading pressure and means for controlling the governor in accordance with the loading pressure. In one embodiment, Fig. 1, the flow in the discharge conduit 12 of an axial flow pump or compressor 10 is measured by a pitot tube 17, the upstream and downstream pressures being communicated through pipes 18 and 19 respectively to opposite sides of a diaphragm 22. The upstream pressure is also communicated to a chamber 33 closed by a bellows 34. The latter is connected to a pivoted lever 35 carrying a follower engaging a pivoted cam 37. An extension on the cam engages the end of a hollow tube 42 so as to restrict the discharge therefrom. The tube 42 is connected to and opens through the end of a bellows 43 closing a chamber 44. The latter is supplied with air under pressure from a pipe 46 by way of a pressure regulator 47 and an orifice 48. Movement of the cam 37 in response to variations in the pressure in pipe 18 causes variation of the restriction of the discharge end of the tube 42. The resultant variation in the pressure in chamber 44 is communicated through line 26 to one side of a diaphragm 25. A pivoted beam 23 under the joint control of diaphragms 22 and 25 thus takes up a position dependent on both flow and discharge pressure. The beam is connected by a link 27 or by a power relay mechanism to an adjustable bleed valve 28. The latter controls the supply of control fluid from a line 31 to a regulator 15 which actuates a blow-off valve 14 at the compressor discharge. In addition, the blow-off valve is opened by a governor 13 if the speed of the driving turbine exceeds a safe value. In the embodiment shown in Fig. 2, the blow-off valve 55 is actuated by a power unit 69 under the control of a weigh beam 68. The beam is jointly controlled by a diaphragm 71 sensitive through pipes 72 to the pressure drop across a flow-measuring restriction 73 in the inlet conduit 53 of the compressor 50 and by a diaphragm 67 supplied with loading pressure from a manually controlled pressure regulator 56. The governor 52 of the driving turbine 51 is controlled by fluid supplied through a nozzle 64 under the control of a weigh beam 59. The beam is jointly controlled by a diaphragm 58 exposed to the loading pressure through a pipe 57 and by a diaphragm 61 connected through a pipe 62 to the compressor discharge conduit 54.