Whether the eccentric reducer at the inlet of centrifugal pump is installed on the top or bottom

To understand this reason, first understand a knowledge point: cavitation phenomenon. Of course, if you only do industrial installation, you don’t need to know so much, because there are complete and correct installation methods in the instructions of each pump manufacturer, and you only need to construct according to the drawings.

20210814013434 73520 - Whether the eccentric reducer at the inlet of centrifugal pump is installed on the top or bottom

Cavitation

Working principle of centrifugal pump: the driving machine drives the impeller to rotate through the pump shaft to generate centrifugal force. Under the action of centrifugal force, the liquid is thrown to the impeller outlet along the blade channel, and the liquid is collected through the volute and sent to the discharge pipe. The liquid obtains energy from the impeller to increase the pressure energy and speed energy, and relies on this energy to transport the liquid to the working place. When the liquid is thrown to the impeller outlet, a low pressure is formed at the center of the impeller inlet, and a pressure difference is generated between the liquid in the suction tank and the liquid in the impeller center. Under the action of this pressure difference, the liquid in the suction tank continuously enters the impeller through the suction pipeline and the suction chamber of the pump.
According to the working principle of the centrifugal pump, the liquid flow flows into the impeller under the action of the pressure difference (PA PK) formed between the suction tank pressure PA and the minimum pressure PK at the impeller inlet. The lower the pressure PK at the impeller inlet, the greater the suction capacity. However, if PK decreases to a certain limit value (at present, the saturated steam pressure pt of the liquid at the conveying temperature is mostly the critical value of the liquid vaporization pressure), cavitation will occur.

Serious consequences caused by cavitation.

  • (1) Generate vibration and noise.
  • (2) It has an impact on the working performance of the pump: when cavitation develops to a certain extent, a large number of bubbles will be generated, which will block the flow channel and significantly reduce the flow, head and efficiency of the pump.
  • (3) The material of the runner will be damaged: mainly due to the fatigue erosion of the metal near the blade inlet.

The methods to improve the cavitation resistance of centrifugal pump.

  • A. Improve the pump structure and reduce Δ HR, it is a pump design problem.
  • B. Improve the effective NPSH in the device: the most important and common method is to use the filling head suction device.

In addition, try to reduce the resistance loss of the suction pipeline and reduce the saturated vapor pressure of the liquid, that is, when designing the suction pipeline, try to choose measures such as larger pipe diameter, shorter length, fewer elbows and valves, and lower temperature of the liquid to be transported, which can improve the effective cavitation allowance of the device.
Well, after understanding the above knowledge points, let’s take a look. What is the role of big and small heads? It is used to change the size of pipe diameter. So what’s the use of changing the pipe diameter at the inlet and outlet of the pump? It is mainly to reduce the flow velocity of the medium in the pipeline, so as to reduce the friction when the medium flows in the pipeline.
The horizontal eccentric reducer at the inlet of centrifugal pump is generally arranged at the top level, but when the reducer is directly connected with the upward bend elbow, the bottom level arrangement can be adopted. The reducer shall be close to the pump inlet. The reason for top flat installation is to prevent gas from accumulating in the eccentric reducer and entering the centrifugal pump, resulting in cavitation damage to the pump. When the inlet diameter of the horizontal suction centrifugal pump is changed, the top level installation is adopted for the pipe from bottom to top, and the bottom level installation is adopted for the pump from top to bottom (top level installation is also adopted to prevent gas accumulation at the pump inlet). The bottom level installation is adopted for the medium with impurities and the suction speed is lower than the impurity settlement speed. The principle is not to form air bags.

It is generally “flat at the bottom from the top and flat at the top from the bottom”.

Source: Network Arrangement – China Eccentric Reducer Manufacturer – Yaang Pipe Industry Co., Limited (www.metallicsteel.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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