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Centrifugal pump

What is a centrifugal pump?

A centrifugal pump is a mechanical device designed to move a fluid by transferring rotational energy from one or more driven motors, called impellers. The fluid enters the rapidly rotating impeller along its axis and is discharged by centrifugal force along its circumference through the ends of the impeller blades. The action of the blade increases the speed and pressure of the fluid and also directs it towards the pump outlet. The pump housing is specially designed to clamp the fluid from the pump inlet, direct it to the impeller and then decelerate and control the fluid before draining.

How does a centrifugal pump work?

The impeller is the main component of a centrifugal pump. It consists of a series of convex fins. These are normally sandwiches between two disks (a closed impeller). For liquids with drift solids, an open or semi-open impeller (supported by a disc) is preferred (Figure 1). Fluid enters the impeller on its axis (the "eye") and exits along the circumference between the fins. The impeller, on the opposite side of the eye, is connected via a drive shaft to a motor and rotates at high speed (typically 500-5000rpm). The rotary motion of the impeller accelerates the fluid outwards through the impeller blades inside the pump housing. There are two basic designs of pump housing: spiral and diffuser . The purpose of both designs is to translate fluid flow into a controlled discharge under pressure. In a ball housing, the impeller is displaced, effectively creating a curved hopper with an increasing cross-sectional area toward the pump outlet. This design causes the fluid pressure to increase towards the outlet (Figure 2). The same basic principle applies to diffusion plans. In this case, the fluid pressure increases as the fluid is extruded between a set of fixed vanes surrounding the impeller (Figure 3). Diffuser designs can be adapted to specific applications and therefore can be more effective. Volute cases are best suited for applications involving entrained solids or high viscosity fluids when it is advantageous to avoid added diffusion fin contractions. Cylinder design asymmetry can lead to greater wear on the impeller and drive shaft.

What are the main features of a centrifugal pump?

There are two main families of pumps: centrifugal and positive pumps displacement . Compared to the latter, centrifugal pumps are typically designed for higher flows and for pumping liquids of lower viscosity, up to 0,1 cP. In some chemical plants, 90% of the pumps used will be centrifugal pumps. However, there are some applications for which positive displacement pumps are preferred.

What are the limitations of a centrifugal pump?

The efficient operation of a centrifugal pump is based on the constant, high speed of rotation of the impeller. With high viscosity feeds, centrifugal pumps become increasingly inefficient: there is more resistance and more pressure is required to maintain a certain flow rate. In general, centrifugal pumps are suitable for applications of low pressure, high capacity, pumping liquids with viscosities between 0,1 and 200 cP. Slurries such as mud or high viscosity oils can cause excessive wear and overheating causing damage and premature damage. Positive displacement pumps often operate at significantly lower speeds and are less prone to these problems. Any pumped medium that is sensitive to shear (separation of emulsions, slurries or biological fluids) can also be damaged by the high speed of the impeller centrifugal pump. In such cases, the lowest speed of a positive displacement pump is preferred. An additional limitation is that, unlike a positive displacement pump, a centrifugal pump can not provide suction when it is dry: it must first be injected with the pumped fluid. Therefore, centrifugal pumps are not suitable for any application where the supply is intermittent. In addition, if the supply pressure is variable, a centrifugal pump produces a variable flow. a positive displacement pump is not sensitive to changing pressures and will provide stable performance. Thus, in applications where precise dosing is required, a positive displacement pump is preferred. The following table summarizes the differences between centrifugal and positive displacement pumps. Pump comparison: Centrifugal versus positive displacement

What are the main applications for centrifugal pumps?

Centrifugal pumps are commonly used to pump water, solvents, organics, oils, acids, bases and any "fine" liquids in industrial, agricultural and domestic applications. In fact, there is a centrifugal pump design suitable for almost any application involving low viscosity fluids.

Summary

A centrifugal pump operates by transferring rotational energy from one or more driven motors, called impellers. The action of the impeller increases the speed and pressure of the fluid and directs it to the outlet of the pump. With its simple design, the centrifugal pump is understandable and easy to operate and maintain