Main principles of pumps selection The selection of the pumping equipment is a crucial point that determines both process parameters and the in-use performance of the unit under development. During the selection of the type of pump three groups of criteria can be distinguished: Process and design requirements Nature of pumped medium Key design parameters Process and design requirements: In some cases, the pump selection is determined by some stringent requirements for a number of design or process parameters. Unlike piston-type pumps, centrifugal pumps can provide uniform delivery of pumped medium, whereas in order to meet uniformity condition on a piston-type pump its design has to be made noticeably complicated, by arranging on the crankshaft several pistons making reciprocating movements with certain delay from each other.