GB1062948A - Improvements in or relating to centrifugal pumps - Google Patents

Abstract

1,062,948. Centrifugal pumps. SPEEDWELL RESEARCH Ltd. Nov. 2, 1964 [Nov.19, 1963; June 25, 1964], Nos.45545/63 and 26251/64. Heading F1C. In a centrifugal pump having an open impeller for pumping mixtures of gas and liquid, such as air and milk, the centrifugal radial component of the liquid velocity in the pump casing is greater than the centripetal radial component of velocity of the gas bubbles. Preferably the liquid velocity at any point is greater than 0À75 ft./sec. Formulae are given in the Specification for calculating the absolute pressure of the liquid at the impeller blade tips, the centrifugal liquid velocity, the centripetal bubble velocity and the radius R Be at which these velocities are equal. In theory, in order to avoid vapour lock the radius of a gas cavity 47 which forms at the centre of the impeller must not exceed the radius R Be . However, the distortion 48 of the cavity 47, in the vicinity of the outlet must be taken into account, which distortion increases when the size of outlet is decreased, as shown in dash lines. There is no pressure recovery in the liquid in the pump outlet duct 41. A nozzle 42 in the duct 41 prevents pressure recovery in the liquid immediately downstream relative to the liquid immediately upstream. The outlet slot has a dimension parallel to the impeller axis equal to the casing width and a dimension D at a maximum value of 0À423 R 1 , the nozzle 42 being positioned downstream of the cutwater 53 a distance E of not less than D-d.