How Does A Single-stage Centrifugal Pump Work?

Oct 18, 2024

A single-stage centrifugal pump refers to a centrifugal pump with an impeller. Due to its high efficiency, simple structure, and many other advantages, single-stage centrifugal pumps are widely used in industrial, agricultural, and daily life to transport materials such as clean water, mud, acid, alkali, salt solutions, and liquid organic matter.
1, Working principle of single-stage centrifugal pump:
Before introducing the working principle of a single-stage centrifugal pump, let's first conduct a simple experiment. Use a basin, fill it with water, and stir the water in the basin by hand in a circular motion. As the speed of hand stirring increases, the speed of circular motion of the water in the basin also increases. The water in the middle of the basin rushes towards the edge of the basin, eventually overflowing from it. Why does water overflow from around the basin? This is due to the centrifugal force generated by water during its circular motion. Any object undergoing circular motion will generate centrifugal force. A centrifugal pump is a device that utilizes the centrifugal force generated by the rotation of a liquid to transport it.
The main working component of a centrifugal pump is the impeller, which contains 6-8 backward curved blades that drive the liquid to rotate. The impeller is fastened to the pump shaft inside the pump casing. The suction port of the pump is located at the center of the pump casing and connected to the suction pipe. The discharge port of the pump is connected to the discharge pipe in the tangential direction of the pump casing; The starting point of the suction pipe is equipped with a bottom valve to prevent the liquid in the pump from flowing back into the storage tank during parking. The function of the filter screen below the bottom valve is to prevent debris from entering the pipeline. A regulating valve is installed on the discharge pipeline to adjust the liquid flow rate, and a check valve should also be installed to prevent accidents caused by liquid backflow during parking. When the electric motor drives the impeller to rotate through the pump shaft, the liquid is sucked into the pump through the suction pipe from the center of the pump casing, then discharged in the tangential direction of the pump casing, and finally sent to the destination through the discharge pipeline.
Before starting a single-stage centrifugal pump, the pump should be filled with the liquid being transported to fill the suction pipeline and pump casing. After startup, the high-speed rotating impeller drives the liquid between the blades to rotate together. Under the action of centrifugal force, the liquid moves outward from the impeller along the flow channel between the blades, is thrown out from the end of the blades, and enters the spiral pump casing. At this time, the flow velocity is relatively high, reaching 15-25m/s, which increases the kinetic energy; Meanwhile, due to the centrifugal force of the liquid itself, the static pressure energy of the liquid is also increased. After the liquid enters the pump casing, due to the gradual expansion of the flow channel area in the volute shaped pump casing, the flow velocity of the liquid gradually decreases, converting some kinetic energy into static pressure energy. At the pump outlet, the static pressure energy of the liquid further increases and is finally discharged from the discharge pipe. At the same time, due to the liquid at the center of the impeller being thrown out, a low-pressure zone is formed, resulting in a pressure difference between the atmospheric pressure on the liquid surface in the storage tank and the local vacuum at the center of the impeller. Under the action of this pressure difference, the liquid continuously enters the impeller along the suction pipeline to replenish the discharged liquid. The impeller keeps rotating, and the liquid is continuously discharged.
In summary, the working principle of a single-stage centrifugal pump is that the impeller filled with liquid rotates at high speed inside the pump casing, causing the liquid to be subjected to centrifugal force and converting the force into kinetic energy and static pressure energy to be transmitted to the liquid, thereby sucking and discharging the liquid.
If the suction pipe or pump casing of a centrifugal pump is not filled with liquid before starting, or if air leaks during operation, due to the much lower density of air compared to liquid, the centrifugal force generated is small, and the vacuum degree formed at the suction port is low, which is not enough to suck the liquid into the pump. At this time, although the impeller rotates, the liquid cannot be transported, and this phenomenon is called "air binding". To eliminate the phenomenon of "gas binding", it is usually necessary to fill the pump before starting, and fill the suction pipe and pump casing with liquid under the action of the bottom valve; For high flow pumps, in order to reduce resistance losses, bottom valves are often not installed and pumps are not filled. Instead, vacuum pumps are used to suction gas and then start; If the installation position of the centrifugal pump is lower than the liquid level in the storage tank and the outlet of the pipeline is connected to the atmosphere, the inlet and outlet valves of the pump can be opened to automatically fill it with liquid.
It should be noted that when installing and using a single-stage centrifugal pump, the entire inlet of the suction pipe to the inlet of the centrifugal pump should be kept in an upward or horizontal state, without any downward stage. Otherwise, the suction pipe will form a hump shape, and an airbag will be formed at the hump when filling the pump. When the centrifugal pump is running, this airbag will enter the impeller and also form an airbag.