A pump drives a fluid circulating within a closed system. A centrifugal pump moves the fluid with a centrifugal force derived from a rotary motion of the driveshaft. Centrifugal pumps are common in many applications where the delivery of liquids with low viscosity is required. This type of pump is mainly used for increasing liquid pressure by regulating the velocity of the flow.
Fig. 1 Centrifugal Pump (TPM 25T, Walrus Pump Co.)
The fluid pushed by the pump is regarded as the media of the driving force. The applications of centrifugal pumps can be divided into two categories. One is to directly deliver the fluid it deals with, and the other is to facilitate the motion transmission between systems (cylinders). Shortly speaking, centrifugal pumps are perfect for a variety of applications, ranging from domestic, commercial, agricultural, to industrial fields.
Depending on the applications, each centrifugal pump has slight differences. For example, the amount of pressure differentiation determines the number of impellers. The construction of the pump may be altered to fit into the structure of certain applications too. Below are the essential components a centrifugal pump has, regardless of the type.
● Inlet and outlet
The inlet and outlet are where the fluid enters and exits the pump. The inlet is connected to the supply system, usually a tank. As for the outlet, it directly connects to the piping of the system.
The impeller generates the centrifugal force to push the fluid through the pump. The main goal of the impeller is to pressurize the fluid as it passes through.
When space allows, or when greater pressure differentiation is needed, there is more than one impeller inside the pump. The pump that contains several impellers is called a multistage pump. As the fluid passes through the impellers, the pressure keeps rising until it is forced out of the outlet.
● Driveshaft (Rotor)
The driveshaft is the power source of the pump. In the pump casing, the shaft is wrapped by the impeller(s) that rotates along its axis. Once the driveshaft rotates, it generates the force to drive the impeller(s). The driveshaft is also called the rotor.
In addition to the radial load, there is also axial load produced as the fluid passes the impeller. With the bearings, they can ensure the alignment of the driveshaft and the impeller, making sure a smooth operation of the pump.
● Mechanical seals
The mechanical seals are arranged between the driveshaft and bearings. They are used to prevent leakage of liquid by sealing the intervals in these two components.
The casing (or housing) is the part that brings together all the components of a pump. The construction of the casing is supposed to be rigid as it is required to withstand the pressure while providing protection of the pump components. Corrosion resistance is another required quality. Therefore, the casing is typically made of stainless steel (or steel-based alloys coated with corrosion-resistant materials).
As mentioned above, centrifugal pumps are used to deliver fluid or drive the motion between devices, so they work on the basis of fluid flow. As fluid enters the pump from the inlet, the driveshaft rotates and the centrifugal force facilitates the advancement of the fluid. The impeller helps increase the pressure of the fluid until it discharges from the outlet.
Centrifugal Pumps, Convergence Training
Despite the same operating principle, the structures can determine which applications and industries a particular pump is suitable for. In addition to the number of impellers, how the components are arranged in the pump casing matters as well. There are two main types of structure. One is with a volute casing, and the other contains diffuser vanes inside the circular pump casing.
Differences between Volute and Diffuser Centrifugal Pump, Technical Engineering School
The volute casing provides a gradually enlarged cross-sectional area from the inlet to the outlet. With the enlargement of the channel, the pressure of the liquid is increased accordingly. As for the diffuser vanes with a generally designed casing, it is the slowed-down flow that increases the liquid pressure. Both structures are used in centrifugal pumps.
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