Positive Displacement Pumps - Performance And Application

Tutorialpg. 137The operating principles of positive displacement (PD) pumps differ from centrifugal pumps. This basic difference is evident in the pump’s response to a system’s head/flow curve. Several pump applications are presented to illustrate the selection process needed to insure pump reliability. The performance overlap region, where both pump types should be considered, is presented with guidelines to evaluate proper selection decisions. The data that must be supplied in PD pump specifications are detailed both in definition of terms and their significance. Many engineering courses devote considerable emphasis to centrifugal pumps and system response but omit positive displacement discussion. Specifying a positive displacement pump without prior training is a difficult task. Technical requirements, performance limitations and terminology are presented to assist the person specifying a PD pump. The PD pump range of operating conditions is presented in several examples to illustrate problems that can be overcome with a properly specified pump. Fluids with large gas fractions or high viscosities cannot be moved with standard centrifugal designs. PD pumps allow a wider range of liquids, slurries and foams to be transported without product degradation. Understanding where PD pumps can be used may lead to opportunities to improve processes