Book - School of Science and Technology

Pumps 20510% increasein speedTwo pumps in seriesPressure5% increasein diameterof impellerPressureTwo pumpsin parallelDatumSinglepump(a)(b)VolumeVolumeFigure 8.2 Centrifugal pumps. Duty change and alternative applicationsvolume/pressure characteristic as was used in part (b) of the preceding diagram, butdrawn to a smaller scale. It will be seen that two identical pumps which are operating inparallel will deliver twice the original volume for any given pressure and, similarly, thattwo identical pumps which are operating in series will produce twice the original pressurefor any given volume. In instances where two dissimilar pumps are arranged to operate ineither parallel or series, the result may be unsatisfactory and a detailed examination of thecharacteristic performance of each must be undertaken.Centrifugal pumps for water systemsPassing from the general to the specific, there are a number of types or styles of centrifugalpump available for application to water heating systems, and these fall into groups whichmay be listed as follows:. form of volute ± split casing or end suction. drive arrangement ± close-coupled, direct or belt. shaft axis ± horizontal or vertical.SplitcasingOutboardbearingFlexible couplingto motorEnd elevation(a)Plan(b)Figure 8.3 Centrifugal pumps. Forms of volute