MICROFICHE REFERENCE LIBFUUW - Cd3wd.com

Another parameter, suction specific speed is defined as(Note that for double suction impellers, Q equals half total dischargethrough the pump. ) This number is used primarily for indexing the cavi-tationperformance of a pump.Also included in Figure 4.1 are typical shapes of pump performancecurves as they very from radial to axial flow impellers. By reveiwingthese curves, some of the different performance features of variousrotodynamicpumps can be observed.Although the regenerative pump is not in the radial/mixed/axial familyof rotodynamic pumps, it also has distinctive curves. The performancecurves resemble, in shape only, those of an axial flow pump. This is, powerand head are both a maximum at shutoff. However, regenerative pumps usuallyhave a discharge range of l-200 gpm and single stage heads of up to about500 feet, while propeller pumps have been built to handle upwards of100,000 gpm but are limited in head to about 30 feet (Pillai, 1969).Specific speeds of regenerative pumps are the lowest of the rotodynamicclass, ranging from 500-1300.Two additional aspects of rotodynamic pump operation are importantto their application; capacity regulation and priming. Unlike positivedisplacement devices, head may vary significantly with changes in the dischargeof a rotodynamic pump. As Smeaton found in the 18th century,discharge, head, and power vary by definite proportions for small chargesin pump speed or impeller diameter. Using performance curves with constant