Energy Saving in Centrifugal Pumps by Impeller Trimming

Abstract

Impeller trimming is a simple and effective method to reduce the flow rate and the power input of acentrifugal pump. The well-known affinity laws for centrifugal pumps state that power input varies withthe cube of impeller diameter, and flow rate varies with impeller diameter. This means that the directapplication of the affinity laws leads to the conclusion that power input varies with the cube of flow rate.However, this conclusion may lead to an inaccurate estimation of energy saving from impeller trimmingin practice. This paper presents a method for providing a better estimate of energy saving. This methoduses pump performance curves supplied by pump manufacturers to estimate the power input required by apump having an arbitrary impeller size. It is shown that both head curve and efficiency curve can beapproximated by quadratic functions. Together with the assumption that the system curve is also aquadratic function, the presented method is capable of producing curves of pump power input at selectedvalues of static head. The analysis of energy saving from impeller trimming shows that the directapplication of the affinity laws to estimate energy saving may be used when the static head is zero or verysmall. A large static head, however, may give rise to a significant overestimation of energy saving.