- Determine the Capacity Required (Unit- M3/Hr)
- Determine the Viscosity of the Liquid (Unit-Centistokes)
- Determine the Differential Pressure of the System (Unit-Meter)
- Pumps with the Best efficiency point at the design operating point should be selected.
Best efficiency point is the operating point at which a pump most efficiently converts shaft power to flow. Higher energy efficiencies are achieved by selecting the pump to operate as close as possible to the BEP.
- Do not oversize pumps. This leads to uneconomical operation and generally narrows the safe operation range of capacities. An oversized pump, while providing sufficient flow, can cause other negative consequences, such as:
Higher purchase costs for the pump and motor assembly.
Larger electrical switchgear and cables.
Higher energy costs.
Higher maintenance requirements; because as pumps operate further from their BEP they experience greater stress.
- Do not try to select pumps with excessively low required NPSH (Net Positive Suction Head).
Do not falsify real available NPSH, trying to keep a margin up your sleeve. This leads to selection of pumps with excessively high Suction Specific Speeds and high minimum flows. A higher NPSH is required when operating to the right of the BEP point which can cause internal cavitation of the pump, thus reducing efficiency and life expectancy of the pump.
- Do evaluate economical advantages of variable speed operation. It is more efficient and results in longer pump life.
- Don't overestimate value of pump efficiency if it's obtained at cost of reliability.
- Following process specification is require while selecting pumps:
System Flow Rate (m3/h)
Total static head (m)
Static Suction Head (m)
Static Discharge Head (m)
Total system Head (m)
Operating temperature of fluid
Nature and size of any solids present.
Single or multiple duty point(s). Multiple duty points occur on pumps that operate to varying process conditions where the pump delivers varying flow rates (m3/hr).
Medium being pumped, e.g. Types of chemical, raw water, potable water, sewage.
Suction conditions i.e. flooded or suction lift
- In selecting a pump, there are two components to consider, the pump and the motor. High efficiency motors not only reduce energy consumption by reducing losses, they also result in additional benefits such as a lower temperature rise in the motor, leading to longer life for the motor and bearings. Motors used in connection with VFD’s(Variable Frequency Drive) should have properly insulated windings to handle the harmonics and other power quality issues associated with VFD’s. As a rule of thumb motors should be rated to operate continuously 15% above BEP design power.