One, cavitation of liquid at a given temperature, reducing the pressure and the temperature of vaporization pressure, liquid bubble. This phenomenon is called cavitation bubbles. Cavitation bubbles generated at the flow to the high pressure, when the volume is reduced, so that burst. This due to the pressure of rising bubbles disappear in the liquid in the phenomenon called cavitation bubble collapse. Pumps in operation, if the flow of the local area (usually impeller blade inlet later somewhere ) for some reason, pumping liquid absolute pressure is reduced to the temperature at which the liquid vaporization pressure, liquid in the vaporization, producing large amounts of steam, the formation of air bubbles, when containing a large number of bubble liquid forward the impeller within the high voltage region, bubble around the high pressure liquid causes the bubble sharply reduced and fracture. Condensation in the bubble burst at the same time, the liquid particles at very high speed filling hole, in this moment have very strong water hammer effect, and to the very high impact frequency against the metal surface, the impact should be up to several hundred to several thousand atmospheres, impact frequency of up to tens of thousands of times per second, serious when will the wall thickness of breakdown. In a water pump for generating air bubbles and bubble break the flow components suffered damage process is the process of cavitation of pump. Water pump cavitation after addition of over-current components can have damaging effects, still can produce noise and vibration, and causes the pump performance decline, serious when can make pump liquid interrupt, can not work normally.
Two basic relationships, pump cavitation pump cavitation is conditioned by the pump itself and the two suction device. Therefore, studies the cavitation occurrence condition, should from the pump itself and the inhalation device both to consider, pump cavitation and the basic equations for NPSHC and NPSHR [ NPSH ] = NPSHANPSHA = NPSHR ( NPSHC ) -- NPSHANPSHA NPSHR pump cavitation" ( NPSHC ) -- pump cavitation free type in NPSHA -- also called effective cavitation cavitation device margin, more not easy cavitation; NPSHR -- pump NPSH, also called required NPSH or pump inlet dynamic pressure, the smaller the anti-cavitation performance better; NPSHC -- the critical NPSH, refers to a corresponding drop in pump performance a certain value the NPSH; [ NPSH ] -- permissible NPSH, is to determine the pump use the conditions for cavitation allowance, usually from the [NPSH] = ( 1.1 ~ 1.5 ) NPSHC.
Three, device NPSH calculation of NPSHA = PS / P GVS / 2GPC / P G = PC / G + G HGHCPS / P P
Four, to prevent the occurrence of cavitation measures to prevent cavitation must improve NPSHA, NPSHA" NPSHR can prevent the occurrence of cavitation are as follows: 1. Reducing geometric suction height HG ( or add geometry intrusion height); 2. Reduce the suction loss of HC, this can be managed to increase in diameter, minimize the length of pipe, elbow and accessories; 3. To prevent the long time in the large flow operation; 4. At the same speed and flow, double suction pump, for reducing inlet velocity is not easy, pump cavitation; 5. Pump cavitation, the flow of small or descending speed operation; 6. Pump suction sump of pump cavitation has important implications for; 7. For under harsh conditions in operation of the pump, to avoid cavitation damage, can use the anti cavitation material.
