The issue of variable diameter at the inlet and outlet of centrifugal pumps

This post was last edited by ylb913 on 2015-10-8 08:40. Due to the design of the centrifugal pump’s structure, its inlet and outlet flanges are generally smaller in diameter compared to the diameters of the inlet and outlet pipes. The inlet pipeline is larger in diameter than the device outlet, which is done to reduce the flow velocity in the pump’s inlet pipeline, minimize pressure drop losses, and prevent cavitation in the pump. The diameter of the pump’s outlet pipeline is still larger than that of the pump’s outlet flange; this is also a matter related to the selection of the flow rate in the pipeline. A lower flow rate results in less pressure drop, but higher costs for the pipeline. In such cases, the pump’s head can be set at a lower value, thereby reducing operating costs ； Higher flow rates result in greater pressure drops; higher pump head leads to higher operating power consumption ； Additionally, high flow rates of some media can cause erosion corrosion.

The inlet pipeline is larger in diameter than the device outlet, and this is to reduce the flow velocity in the pump’s inlet pipeline, minimize pressure drop losses, and prevent cavitation in the pump? The pipeline narrows as it moves toward the pump inlet; the flow rate should increase, so why does it decrease?

This classmate, the person upstairs answered very clearly. A larger pipe diameter is used to reduce the flow velocity; at the pump inlet, a slight change in diameter does not cause an increase in the flow velocity throughout the entire pipeline.

I learned it! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !

The diameter of process pipes is determined either by the pump or through process calculations. To put it simply, it’s not the pump that determines the process pipeline; rather, it’s the process pipeline that determines the pump. Since the pump inlet opening is the same size as the pipe, the velocity of the fluid entering the pump must be lower than that in cases where the diameter decreases. A lower velocity results in higher pressure, which makes cavitation less likely to occur.

Firstly, fluid flow requires energy to overcome friction; the narrower the pipe, the higher the flow velocity, the greater the friction, and thus the more energy is consumed. The larger the pipe, the slower the flow rate, the less friction there is, and the less energy is consumed; however, the cost of the pipe is also higher. Therefore, different fluids have their own recommended flow rates; a higher flow rate requires a larger pipe, which is more economical and reasonable. A pump is a device that increases the pressure head of a fluid; the flow velocity of the fluid inside the pump is high, and compared to the pipes, the inlet and outlet flanges of the pump are relatively small, so a reducer is needed to fit them together. Generally, it is recommended that the flow velocity at the pump inlet be lower than that at the outlet; therefore, the pipe at the pump inlet should be larger than the one at the outlet.

The size of the pipeline is determined by taking into account factors such as pressure drop, flow rate, and net positive suction head, as confirmed by the process engineer; whereas the sizes of the pump inlet and outlet are determined by the manufacturer. If the two are not consistent, increase the larger size. There aren’t that many twists and turns

This is related to the working principle of pumps, as a pump is itself a type of fluid machine that accelerates a fluid, increasing its kinetic energy, and then slows it down to convert that kinetic energy into potential energy (pressure). Specifically: the reduction in diameter at the inlet is intended to provide the fluid inside the pump with an adequate initial velocity, while the increase in diameter at the outlet is meant to reduce the flow velocity, thereby converting the kinetic energy of the flow more effectively into potential energy (pressure).