What Are The Structure, Working Principle, And Main Components Of A Centrifugal Pump

Jan 30, 2025

Construction and working principle of centrifugal pump
According to physics, an object undergoing circular motion is subjected to centrifugal force. If the centripetal force is insufficient or lost, the object will fly out along the tangent direction of the circumference due to inertia, forming a so-called centrifugal motion. Centrifugal pumps work by utilizing this inertial centrifugal motion.
Schematic diagram of the basic structure of single-stage centrifugal pumps commonly used in water supply and drainage engineering. Its main working components are impeller 1, volute pump casing 2, and pump shaft 3 that drives the impeller to rotate. The suction port of the snail shaped pump casing is connected to the suction pipe 4 of the water pump, and the outlet is connected to the pressure pipe 7 of the water pump. The impeller with curved blades is installed in a fixed pump casing, and the inlet of the impeller is connected to the water pump suction pipe. Before starting pumping, fill the pump and suction pipe with water. When the power machine drives the impeller to rotate at high speed through the pump shaft,
The water in the impeller rotates at high speed together with the impeller. Due to the insufficient cohesion of the water and the frictional force between the blades and the water to form a centripetal force that maintains the rotational motion of the water flow, the water flow in the impeller gradually flows towards the outer edge of the impeller, is thrown out of the impeller and enters the pump casing, and then flows into the pressure pipe of the water pump through the diffusion cone pipe. It is transported to the pipeline network through the pressure pipe. At the same time, a vacuum is formed at the center of the impeller due to the water being thrown out, and atmospheric pressure acts on the surface of the suction pool. The water in the suction pipe continuously flows into the impeller along the suction pipe under this pressure difference. The continuous rotation of the impeller causes water to be constantly thrown out and sucked in, forming the continuous water delivery of the centrifugal pump.
As mentioned above, the working process of a centrifugal pump is actually a process of energy transfer and conversion. It converts the mechanical energy of the power machine into the kinetic energy and pressure energy of the fluid being transported. In the process of energy transfer and conversion, there are inevitably many energy losses, and the greater the loss, the lower the work efficiency, and the worse the performance of the pump.

Main components of centrifugal pump
A centrifugal pump is composed of many components. Taking a single-stage single suction centrifugal pump as an example, we will discuss the functions, materials, and composition of each main component.
1, Impeller
The impeller, also known as the working wheel or rotary wheel, is used to transfer the mechanical energy of the power machine to the liquid being pumped, increasing the energy of the fluid flowing through the impeller. When selecting impeller materials, in addition to considering the mechanical strength under centrifugal force, the wear resistance and corrosion resistance of the material should also be taken into account. At present, impellers are mostly made of cast iron, cast steel, and bronze.
The impeller is divided into two types according to its structure: single suction and double suction. It absorbs water on one side, and the front and rear cover plates of the impeller are asymmetric. Single suction impeller is used for single suction centrifugal pumps. Double suction impeller, it absorbs water on both sides, and the impeller cover plate is symmetrical. Double suction centrifugal pumps use double suction impellers, which have a large flow rate and can automatically balance axial forces.
The impeller is divided into three forms based on its cover plate: closed, open, and semi open. An impeller with two cover plates is called a closed impeller. Between the cover plates, there are 6-12 blades that bend backwards. This type of impeller has high efficiency and is widely used. An impeller with only a rear cover plate and no front cover plate is called a semi open impeller. An impeller with only blades and no cover plate is called an open impeller. Semi open and open impellers have fewer blades, usually only 2? 5 pieces, these two types of impellers have lower efficiency compared to enclosed impellers and are suitable for 6
Discharging liquids that are contaminated or contain a large amount of solid particles.
2, Pump shaft
The function of the pump shaft is to support and drive the impeller to rotate, transferring the energy of the power machine to the impeller. It is required that the shaft end of the horizontal centrifugal pump be straight and have sufficient strength and rigidity to avoid impeller swing caused by shaft bending during pump operation, which may cause damage to the impeller and pump casing due to wear. The pump shaft is generally made of carbon steel or stainless steel. One end of the pump shaft is fixed to the impeller with a flat key and a reverse nut, ensuring that the impeller is tightened during rotation; In large and medium-sized water pumps, the axial position of the impeller is located using shaft sleeves and nuts that tighten the shaft sleeves. Install a coupling on the other end of the pump shaft.
3, Pump casing
The pump casing of a centrifugal pump is in the shape of a snail shell that contains and transports liquids. It consists of a pump cover and a snail body. The pump cover is the suction chamber of the pump, which functions to evenly guide the water in the suction pipe towards the impeller with minimal loss. According to the structure, suction chambers can be divided into straight conical suction chambers, annular suction chambers, and semi spiral suction chambers. The snail body is composed of a snail chamber and a diffuser cone. The main function of the snail chamber is to collect the water flow thrown out by the impeller and maintain a constant water flow velocity in the snail chamber by continuously increasing its flow cross-section, in order to reduce head loss. After being discharged from the snail chamber, the water flows into the pressure tube through the diffusion cone tube. The function of the diffusion cone tube is to reduce the velocity of the water flow and convert some of the kinetic energy of the water flow into pressure energy.
There are two drilled holes at the inlet and outlet flanges of the pump casing, which are used to install vacuum gauges and pressure gauges for measuring the inlet and outlet pressure of the pump. The top of the pump casing is equipped with a water filling (or air extraction) hole, which is used to fill water or extract air from the pump casing before starting the water pump. The bottom of the pump casing is equipped with a drain hole for emptying the accumulated water inside the pump after stopping, to prevent freezing in winter. The bottom of the pump casing is equipped with bolt holes for fixing to the foundation. Except for the bolt holes that fix the water pump, other screw holes need to be plugged with threaded plugs when the water pump is not in use temporarily.
Among the above components, the impeller and pump shaft are the rotating parts of a vertical centrifugal pump, while the pump casing is a fixed component. There are three junctions between these two: the shaft seal device between the pump shaft and the pump casing, the leak reducing ring at the joint between the impeller and the inner wall of the pump casing, and the bearing at the rotational connection between the pump shaft and the pump seat.