| Characterization of pump performance parameters pump NPSH is allowe |
| Author:Shijiazhuang Zurish Industry Pump Co., Ltd Time:2017-11-06 08:46:57 Visits:551 |
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The allowable cavitation allowance of the pump is a safe margin that the pump requires to ensure that no cavitation occurs.
When centrifugal pump impeller at the entrance of the fluid pressure drop to conveying liquid temperature of saturated vapor pressure, the liquid will vaporize, also may be dissolved in the liquid inside the escape of gas from the liquid, forming a large number of small bubbles. When these small bubbles with the liquid flow in the impeller passage pressure is higher than the critical value of the area, due to the stress inside the bubble is vaporized, outside, liquid pressure higher than the evaporation pressure, then around the small bubbles in the liquid pressure, condensation, breaking again. Within the impeller, when the small bubble condensation, crush, like form a hole, then the fluid surrounding the made for the holes at high speed, liquid particle collisions forming local hydraulic impact, the partial pressure can reach hundreds of atmospheric pressure. The larger the vapor bubble, the more local water pressure caused by its condensation and collapse. If these bubbles are to be destroyed on the surface of the impeller metal, the liquid point is like numerous small warheads, continuously hitting the metal surface. This type of hydraulic shock, with a fast speed and a frequency of up to 2500L/S, can cause gradual fatigue damage to the surface of the material, resulting in the erosion of the metal surface, resulting in the appearance of honeycomb cavitation holes. If the steam mixed with some kind of active gas inside the bubble, such as oxygen, etc.), they use bubble condensation when gives off heat, the local temperature can reach 200-200 ° C, electrochemical corrosion to metal, more accelerated the damage of the metal. The vaporization, condensation, impact of the above gas and the comprehensive phenomenon of metal denudation are called cavitation.
Cavitation process is not stable, lead to pump vibration and noise, at the same time due to cavitation bubble plug impeller groove, so the capacity and head are reduced, the efficiency drop, serious when not working. Therefore, when the pump is working, it must prevent cavitation. Once the cavitation occurs, stop the pump immediately, close the inlet valve, pump the pump thoroughly, refill the pump, make sure the pump is filled with liquid and then start again.
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