Cavitation phenomenon of the pump liquid at a certain temperature, reducing pressure to the temperature of the vaporization pressure, the liquid will produce bubbles. The phenomenon of bubbles is called cavitation. Cavitation bubble generated when flowing to high pressure Department, the volume decreases so as to burst. This phenomenon of bubble disappearing in liquid due to pressure increase is called cavitation collapse. When the pump is in operation, if the localized area of ​​the overcurrent portion (usually somewhere later in the impeller vane inlet) for some reason causes the absolute pressure of the pumped liquid to drop to the liquid vaporization pressure at the current temperature, Began to vaporize, produce a lot of steam, the formation of bubbles, when the liquid containing a lot of bubbles forward through the high-pressure area within the impeller, the bubbles around the high-pressure liquid bubbles so sharply reduced to rupture. At the same time as the bubble is broken and condensed, the liquid particles fill the cavity at a very high speed, causing a very strong water hammer moment at this moment, and striking the metal surface with a high impact frequency with an impact stress of several hundreds to several thousands Atmospheric pressure, the impact frequency of up to tens of thousands of times per second, will be severe wall breakdown. Cavitation in a pump is the process by which bubbles in the pump and rupture of the bubble damage the overcurrent component. Pump cavitation in addition to the over-current components will have a damaging effect, but also produce noise and vibration, and lead to the decline in the performance of the pump, serious pump liquid will be interrupted, can not work properly. Pump cavitation Basic relationship Pump cavitation conditions are determined by the pump itself and the inhalation device in two aspects. Therefore, to study the conditions of cavitation should be considered from both the pump itself and the inhalation device, the basic equation for the pump cavitation is NPSHC≤NPSHR≤NPSH≤NPSHANPSHA = NPSHR (NPSHC) -the pump starts cavitation NPSHANPSHA "NPSHR (NPSHC) - No cavitation in pumps NPSHA - Equivalent NPSH, also known as effective NPSH, is more difficult to cavitate; NPSHR - NPSHR, also called required NPSH Or pump dynamic pressure drop, the smaller the better anti-cavitation performance; NPSHC - critical NPSH, which corresponds to the decline in pump performance NPSH; NPSH - allowable NPSH , Is to determine the conditions for the use of pumps NPSH, usually take ã€NPSH】 = (1.1 ~ 1.5) NPSHC
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