An old question: the reasons for the diameter change in the pump’s inlet and outlet pipes

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The inlet and outlet pipes of a pump usually have diameter changes: from the inlet pipe to the pump, the diameter decreases, while from the pump outlet to the outlet pipe, the diameter increases! What is the reason for this? Based on comprehensive online information regarding the reasons for inlet diameter variation: the pump’s suction inlet is a low-pressure area. When the lowest pressure near the inlet of the blade is equal to or less than the saturated vapor pressure of the liquid at the conveying temperature, the liquid will vaporize, or the gas dissolved in the liquid will come out and form bubbles. When the liquid containing bubbles enters the high-pressure area of the impeller, the bubbles shrink rapidly and burst under the high pressure of 9 k7 y6 m+ B, m: F# L' v. The disappearance of these bubbles creates a local vacuum, causing the surrounding liquid to rush toward the site where the bubbles burst at high speed. It causes 4 {8 a2 J) j. c/ D1 d vibration and shock. Under repeated exposure to high impact forces, the blades will be damaged. 3 / Z& e) a- c% e – this is when cavitation occurs. 8 To avoid cavitation, it is necessary that the sum of the static head and dynamic head of the liquid at the pump inlet be greater than the saturated vapor pressure of the liquid at the operating temperature. The purpose of reducing the diameter is to increase u. The dynamic head u2/2g increases. The purpose of enlarging the outlet diameter is to convert kinetic energy into pressure energy!