Centrifugal Pump concept
A centrifugal pump is a mechanical device designed to move fluid by transferring rotational energy through single-stage or multi-stage impellers installed on the driven rotor. The fluid enters the rapidly rotating impeller along its axis and is discharged by centrifugal force along its circumference through the blade tip of the impeller. The role of the impeller increases the speed and pressure of the fluid and directs it to the pump outlet. The pump casing is specially designed to compress the fluid at the pump inlet, guide it into the impeller, and then decelerate and control the fluid before discharging.
Centrifugal Pump Working Principle
Impeller is the key part of centrifugal pump. It consists of a series of curved blades. They are usually sandwiched between two circular covers (closed impellers). For fluids with solids, open or semi open impellers (supported by a single circular cover plate)are preferred, see Figure 1.
Figure 1: Impeller type- Open, semi-open
Fluid enters the impeller from the axis ("eye") direction of the impeller and flows out along the circumferential direction between the blades. On the other side of the impeller "eye", it is connected to the drive machine (usually the motor) through the drive shaft and rotates at high speed (usually 500 rpm - 6000 rpm). The rotating movement of the impeller accelerates the fluid to enter the pump housing through the impeller blade.
There are two basic designs of the pump housing: the volute and the diffuser (also called "guide vanes"). The purpose of both designs is to convert the fluid flow into a controlled discharge under a certain pressure.
In the volute, the impeller is offset, effectively forming a curved channel with a gradually increasing cross-sectional area toward the pump outlet. This design increases the fluid pressure towards the outlet, as shown in Figure 2.
Figure 2: Spiral case design
The same basic principles apply to diffuser design. In this case, when the fluid is discharged between a set of fixed blades around the impeller, the fluid pressure increases (Fig. 3). The diffuser design can be customized for specific applications, so it is more efficient. The volute is more suitable for applications involving entrainment of solids or highly viscous fluids, as it helps to avoid the additional binding caused by diffuser blades. The asymmetry of volute design will lead to increased wear of impeller and drive shaft.
Figure 3:Diffuser design
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