When selecting a pump it is important to determine the required flow and pressure to be generated by the pump. The flow may be determined by a process requirement, by the heating or cooling required in the system or by the peak water demand for utilities. The pressure required may be to elevate the liquid within the system or to overcome the pressure losses in the system created as liquid passes through it.

It is important to know as much about the pump system as possible and to create a pressure/flow profile for the system. The energy required to drive the pump is directly related to the flow and pressure required. To generate high pressures generally leads to designs which may be innefficient and therefore it is important that neither the flow nor pressure are overspecified.

Pumps generally fall into two types, rotary, more normally called positive displacement (PD) or rotodynamic, more normally called centrifugal pumps.

If the capacity is going to be very low a positive displacement (PD) pump would normally be recommended.

Between 5 m3 /hr - 115 m3/hr a single stage end suction centrifugal pump would be normal.

At higher capacities a double suction design with a wide impeller or two pumps in parallel may be selected.

If a high head, low capacity pump is required there may be several options. A positive displacement, high speed centrifugal or multi-stage pump may be offered.

Whatever type of pump is selected, it will have been designed for a specific flow and pressure and will attain its maximum efficiency at that design point (its Best Efficiency Point - BEP). If the pump is operated away from its BEP it will be increasingly inefficient and may suffer mechanical damage or reduced operating life. It is important to select a pump to operate close to its BEP.

For centrifugal pumps that operate on Water, it is possible to determine whether the pump selected is close to the maximum attainable efficiency by using the Europump Guide to Pump Efficiency for Single Stage Centrifugal Pumps which can be downloaded here. Click here to download this file

Comparing the efficiency of the pumps offered by different manufacturers will be a guide to the maximum attainable but it should be noted that pump selection is a complex process and the liquid pumped will have a significant effect on the type of pump offered. Maximum efficiency may not be possible with for example a sewage pump where anti clogging, abrasion resistance and reliability may override this.

In the case of dangerous liquids there may be an increase in power consumed in exchange for the safety of using a Sealless pump.

For this reason the concept of life cycle cost must be appreciated The life cycle cost (LCC) of any piece of equipment is the total "lifetime" cost to purchase, install, operate, maintain, and dispose of that equipment. The components of a life cycle cost analysis typically include initial costs, installation and commissioning costs, energy costs, operation costs, maintenance and repair costs, down time costs, environmental costs, and decommissioning and disposal costs. A high percentage of the total LCC costs for a pumping systems installation will be attributed to energy and maintenance costs. Download the Lifetime Cost Calculator here Click here to download this file

To learn more about pump selection download the UK Pump Procurement Guide Click here to download this file