Centrifugal Pump Mechanical Components

Figure 4 illustrates the major components of a centrifugal pump. This is a diagram of a horizontal single-stage, overhung pump which is the most common type. Horizontal refers to the orientation of the shaft; single-stage means there is one impeller, and overhung means that the impeller is outside of the two supporting bearings, not between the bearings.

The shaft runs through the center of the pump and holds the impeller at the left end. The drive motor is connected to the right end of the shaft through a flexible coupling. The liquid enters the suction nozzle, passes through the enclosed sections of the spinning impeller, and exits through the discharge nozzle at the top of the pump. The right end of the pump is the bearing housing. This housing contains two sets of ball bearings that support the weight of the shaft. They also absorb the axial thrust on the shaft.

The casing contains the liquid under pressure. A seal is required where the rotating shaft enters the casing. This area is called the stuffing box and may actually contain a stuffing or packing. However, most modern pumps have mechanical seals at this point. Sealing the shaft is very important to prevent leakage of the pumped fluid, which is frequently hazardous, flammable, or toxic. Therefore, careful attention must be paid to the design, installation, and maintenance of the seals. Many different types of seals are available for different process conditions.

Heat is generated by friction in seal area of the shaft, and sometimes cooling is required. A channel called the flushing connection (lantern ring connection) is available for this purpose.

Impellers may be the open, semi-closed, or closed. These are shown in Figure 5. In the petroleum and gas process plants, most impellers are the closed type. Closed impellers can generate higher heads at greater efficiencies. Open and semi-closed impellers are used for liquids that contain solids. They will not clog as easily as closed impellers.

Figure 6 shows other common types of centrifugal pumps. The amount of head that can be generated by a single impeller is limited to a maximum value. If more head is required, pump designs incorporate two or more impellers. These may be arranged in a horizontal multistage configuration or a vertical multistage configuration.

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