Centrifugal Pumps

Centrifugal pumps are mechanical devices suitable for transporting fluids with high flow rate and low viscosity. They are also used for applications in the oil and gas, manufacturing, pharmaceutical, chemical, textile, rubber, and power sectors.

Centrifugal pumps operate by transferring energy from a rotating impeller to the fluid, which is inside a casing. Fluid enters the rapidly rotating impeller along its axis and is cast out by centrifugal force along its circumference through its vane tips. The action of the impeller increases the fluid’s velocity and pressure and directs it towards the pump outlet.

The characteristics of centrifugal pumps are:

• Modular construction, high interchangeability, fast delivery.
• Versatile shaft sealing arrangement, gland packing as a standard arrangement, and option to use the mechanical seal.
• Process type design results in minimum downtime.
• Back pull-out design enabling easier removal for inspection and maintenance.
• The pump comes in 3 bearing designs resulting in a good continuous process with high productivity.
• Below are factors that affect the performance of a centrifugal pump and need to be considered while choosing a centrifugal pump:

Working Fluid Viscosity: can be defined as resistance to shear when energy is applied. In general, a centrifugal pump is suitable for low viscosity fluids since the pumping action generates high liquid shear.

Specific Density and Gravity of Working Fluid: The density of a fluid is its mass per unit of volume. A fluid’s mass per unit volume and gravity of a fluid is the ratio of a fluid’s density to the density of water. It directly affects the input power required to pump a particular liquid. If you are working with a fluid other than water, it is important to consider the specific density and gravity since the weight will have a direct effect on the amount of work performed by the pump.

Operating Temperature and Pressure: Pumping conditions like temperature and pressure are important considerations for any operation. For example – High-temperature pumping may require special gaskets, seals, and mounting designs. Similarly, an adequately designed pressure-retaining casing may be required for high-pressure conditions.

Net Positive Suction Head (NPSH) and Cavitation: NPSH is a term that refers to the pressure of a fluid on the suction side of a pump to help determine if the pressure is high enough to avoid cavitation. Cavitation refers to the formation of bubbles or cavities in a liquid, developed in areas of relatively low pressure around an impeller and can cause serious damage to the impeller and lead to decreased flow/pressure rates among other things. One must ensure that the system’s net positive suction head available (NPSHA) is greater than the pump’s net positive suction head required (NPSHR), with an appropriate safety margin.

Vapour Pressure of the Working Fluid: The vapour pressure of a fluid is the pressure, at a given temperature, at which a fluid will change to a vapour. It must be determined to avoid cavitation as well as bearing damage caused by dry running when the fluid has evaporated.

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