GB737172A - Improvements in and relating to centrifugal pumps and blowers - Google Patents

Abstract

737,172. Centrifugal pumps and blowers. FRANKS & SAUNDERS, Ltd. June 15, 1953 [April 21, 1952], No. 10000/52. Class 110 (1). In a multi-stage centrifugal pump or blower, at least one of the stages is provided with valves controlling a by-pass around the stage, such valves including a main valve which closes the inlet to the by-passed stage and a non-return valve leading from the delivery side of the preceding stage to a point beyond the by-passed stage, each such by-pass being automatically brought into action when the pressure developed by that or a higher stage reaches a predetermined value and out of action when the pressure at the inlet of the by-passed stage falls below a predetermined value. At low speeds of operation, both impellers 10, 11 of a two-stage centrifugal pump are in operation. Water drawn in through the suction 18 passes by way of a conduit 19 and the space between two partitions 20, 21 to the eye of impeller 10. On discharge from impeller 10, the water passes by way of passages 22 and 14 to the eye of impeller 11. Impeller 11 discharges the water through a passage 26 and a flap valve 28 to a discharge chamber 23. When the pressure in chamber 23 rises sufficiently, it lifts a valve 51 against the action of a spring 52 so that water at the discharge pressure passes through a pipe 58 and moves a piston or, as shown, a diaphragm 47 against the action of a spring 49 to close a valve 17, whereby admission to impeller 11 is closed. Impeller 10 then discharges directly to chamber 23 through a flap valve 25, and the flap valve 28 is closed by the pressure in chamber 23. If the pressure in chamber 23 falls again, the valve 51 returns to the position shown and restores the connection of pipe 58 to a pipe 60 leading to waste or the pump suction. Spring 49 then opens the valve 17 and impeller 11 is brought back into operation. To prevent hunting, the diameter of valve 51 is larger than the bore of its seating, so that the valve does not close until the pressure has fallen perceptibly below the value at which it opened. Alternatively, the changeover is arranged to occur at a point of intersection of the performance curves of the pump with and without the controlled stage in operation. A filter gauze 54 is provided at the entry to valve 51. To ensure priming of impeller 10, water is recirculated through passage 35 from a chamber 34 connected to the chamber 23. A chamber 38 is also connected to chamber 23 to provide a supply of cooling water for a seal 37 and to prevent ingress of air. To permit operation in either direction of rotation, the impeller vanes are radial and the parts of the casing in which they run are substantially symmetrical in end view. There may be more than two stages, with a controlled by-pass for every stage except one, the control valves being arranged to open and close at the same pair of pressures, so that they open in order from the last stage downwards. Alternatively, the first non-return valve of each controlled stage may open into the final delivery conduit, in which case the control valves must be set at different pairs of pressures so that the stages are cut in and out in a definite sequence. Specifications 321,892, [Class 135], 434,665, 434,684, 533,116 and 585,607, [all in Group XXIX], are referred to.