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First, the causes of cavitation phenomenon Liquid at a certain temperature, reduce the 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. Impurities In operation, if the local area of ​​the overcurrent portion (usually somewhere later in the impeller vane inlet) is, for some reason, the absolute pressure of the pumped liquid drops to the liquid vaporization pressure at the current temperature, The vaporizer begins to vaporize and generate a large amount of steam, forming bubbles. When the liquid containing a large amount of bubbles moves forward through the high-pressure region inside the impeller, the high-pressure liquid around the bubbles causes the bubbles to shrink sharply 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. The process of creating bubbles and bubble ruptures in water-contaminated pumps that cause damage to overcurrent components is the cavitation process in water-contaminated pumps. In addition to the damage caused by overcurrent components, cavitation pumps produce noise and vibration and lead to the performance degradation of impurity pumps. In severe cases, the impurities in the pump will be interrupted and can not work normally. Second, the basic relationship between impurity pump cavitation impurity pump cavitation conditions are impurities pump itself and inhalation device determined in two ways. Therefore, to study the conditions of cavitation should be considered from both the impurity pump itself and the inhalation device, the basic relationship of impurity pump cavitation NPSHc ≤ NPSHr ≤ [NPSH] ≤ NPSHa NPSHa = NPSHr (NPSHc) - impurity pump start steam NPSHrNPSHr (NPSHc) - NPSHr - Impurity pump without cavitation NPSHa - NPSHr - also known as the effective NPSH, the greater the more difficult to cavitation; NPSHr - impurity pump NPSH, also known as NPSHc - Critical NPSH, which is the NPSH corresponding to the drop in performance of the impurity pump; [NPSH] - Allowable NPSH is the NPSHc used to determine the conditions for the use of impurity pumps. Usually, [NPSH] = (1.1 ~ 1.5) NPSHc. Third, the device NPSHa = Ps / Ïg + Vs / 2g-Pc / Ïg = Pc / Ïg ± hg-hc-Ps / Ïg Fourth, the measure to prevent cavitation To prevent cavitation must be increased NPSHa , So that NPSHa> NPSHr prevent cavitation measures are as follows: 1. Reduce the geometric suction height hg (or increase the geometric inversion height); 2. Reduce the suction loss hc, for which you can try to increase the diameter, minimize pipe length, elbows and accessories, etc .; Prevent long run at high flow rate; 4. In the same speed and flow, using double suction impurity pump, due to reduce the inlet flow rate, impurity pump cavitation easily occur; Impurities pump cavitation occurs when the flow rate should be reduced or reduced speed operation; 6. Impurity pump suction pump cavities have a significant impact on impurities; 7. For impurity pumps that operate under harsh conditions, cavitation-resistant materials may be used to avoid cavitation damage.