Calculation of suction capacity of centrifugal pumps

Information about cavitation characteristics of centrifugal pumps and critical cavitation conditions is given. Depending on the position of the leading edge, impellers are divided into three groups. The spatial lattice of the impeller is presented as a set of elementary lattices on the axisymmetric surfaces of a current of equal-velocity meridional flow. Equations have been derived from the determination of the cavitation margin and the equation of the energy in relative motion for the critical cavitation margin containing a cavitation coefficient referred to the impeller inlet. General equations have been obtained for the critical cavitaion coefficient of specific speed, which can be used to analyze the influence of geometric and operating conditions on the suction capacity of centrifugal impellers, which must be taken into account in designing them. The selection of the typical inlet diameter of the impeller has been substantiated and the critical cavitation coefficients of the elementary lattices have been found. An empirical equation, valid in the whole range of parameters encountered in practice, has been derived for the cavitation coefficient of type-3 impellers with a leading edge located roughly on the diameter of the impeller neck. An analytical equation, applicable for type-1 and-2 impellers, is given for the critical cavitation coefficient with empirical force coefficient values. A scheme for calculation of the suction capacity of such impellers is presented.