READING COMPREHENSION: CENTRIFUGAL PUMP

Centrifugal pump

A centrifugal pump is a rotodynamic pump that uses a rotating impeller to create flow by the addition of energy to a fluid. Centrifugal pumps are commonly used to move liquids through piping. The fluid enters the pump impeller along or near to the rotating axis and is accelerated by the impeller, flowing radially outward into a diffuser or volute chamber (casing), from where it exits into the downstream piping. Centrifugal pumps are used for large discharge through smaller heads.

How it works

Like most pumps, a centrifugal pump converts mechanical energy from a motor to energy of a moving fluid; some of the energy goes into kinetic energy of fluid motion, and some into potential energy, represented by a fluid pressure or by lifting the fluid against gravity to a higher level.

The transfer of energy from the mechanical rotation of the impeller to the motion and pressure of the fluid is usually described in terms of centrifugal force, especially in older sources written before the modern concept of centrifugal force as a fictitious force in a rotating reference frame was well articulated. The concept of centrifugal force is not actually required to describe the action of the centrifugal pump.

In the modern centrifugal pump, most of the energy conversion is due to the outward force that curved impeller blades impart on the fluid. Invariably, some of the energy also pushes the fluid into a circular motion, and this circular motion can also convey some energy and increase the pressure at the outlet

Vertical centrifugal pumps

Vertical centrifugal pumps are also referred to as cantilever pumps. They utilize a unique shaft and bearing support configuration that allows the volute to hang in the sump while the bearings are outside of the sump. This style of pump uses no stuffing box to seal the shaft but instead utilizes a "throttle Bushing". A common application for this style of pump is in a parts washer.

Multistage centrifugal pumps

A centrifugal pump containing two or more impellers is called a multistage centrifugal pump. The impellers may be mounted on the same shaft or on different shafts.

If we need higher pressure at the outlet we can connect impellers in series.

If we need a higher flow output we can connect impellers in parallel.

All energy added to the fluid comes from the power of the electric or other motor force driving the impeller.

Problems of centrifugal pumps

·         Cavitation—the NPSH of the system is too low for the selected pump

·         Wear of the Impeller—can be worsened by suspended solids

·         Corrosion inside the pump caused by the fluid properties

·         Overheating due to low flow

·         Leakage along rotating shaft

·         Lack of prime—centrifugal pumps must be filled (with the fluid to be pumped) in order to operate

·         Surge