First, the phenomenon of cavitation pump technology 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. Centrifugal pump in operation, if the over-flow part of the local area (usually impeller blade inlet somewhere later) for some reason, the absolute pressure of the liquid pumped down to the current temperature of liquid vaporization pressure, the liquid at 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. 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. Second, the basic relationship between centrifugal pump cavitation Centrifugal pump occurs cavitation conditions are determined by the pump itself and the inhalation device. Therefore, to study the conditions of cavitation should be considered from both the pump itself and the inhalation device, the basic relationship of pump cavitation NPSHc≤NPSHr≤ [NPSH] ≤NPSHaNPSHrNPSHc-- pump start cavitationNPSHaNPSHa> NPSHrNPSHc-- pump NPSHa - NPSHa - NPSHr - also known as the effective NPSH, the bigger the more difficult to cavitation; NPSHr - pump NPSH, also known as the necessary NPSH or the import of dynamic pressure drop, NPSHc - Critical NPSH, which is the NPSH corresponding to the drop in pump performance; [NPSH] - Allowable NPSH, which is used to determine the condition of the pump NPSH] = (1.1 ~ 1.5) NPSHc. Third, to prevent the occurrence of cavitation measures To prevent the occurrence of cavitation must improve NPSHa, 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, the use of double suction pump, due to reduce the inlet flow rate, the pump is not prone to cavitation; Centrifugal pump cavitation, the flow should be reduced or reduced speed operation; 6. Centrifugal pump suction pump has a significant impact on cavitation; 7. For pumps operating under harsh conditions, cavitation-resistant materials may be used to avoid cavitation damage.
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