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. 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 both on the pump itself and the inhalation device, the basic equation for the pump cavitation NPSHc ≤ NPSHr ≤ [NPSH] ≤ NPSHa NPSHa = NPSHr (NPSHc) - pump start cavitation NPSHa NPSHa > NPSHr (NPSHc) - No Cavitation in Pumps NPSHa - Equivalent NPSHa, also known as effective NPSH, is more difficult to cavitate; NPSHr - NPSHr, also known as required cavitation NPSHc - Critical NPSH, which is the NPSH corresponding to the drop in pump performance; [NPSH] - Allowable cavitation The margin, is used to determine the conditions of use of the pump NPSH, usually take [NPSH] = (1.1 ~ 1.5) NPSHc. NPSHa = Ps / Ïg + Vs / 2g-Pc / Ïg = Pc / Ïg ± hg-hc-Ps / Ïg Measures to Prevent Cavitation To prevent cavitation, NPSHa must be increased so that NPSHa> NPSHr measures to prevent cavitation occur 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; Cavitation occurs when the pump, the flow should be reduced or reduced speed operation; 6. Pump suction pump cavitation has a significant impact; 7. For pumps operating under harsh conditions, cavitation-resistant materials may be used to avoid cavitation damage. Cavitation-prone pumps are: UHB-ZK wear-resistant corrosion-resistant mortar pump, FZB Fluoroplastic self-priming pump, FSB Fluoroplastics alloy centrifugal pump, GC boiler feed pump, IHF lining fluorine centrifugal pump, FB, AFB corrosion chemical Pump, IH chemical centrifugal pump, CWM screw pump, IHG chemical pipeline pump, IS water centrifugal pump, vertical electric diaphragm pump, lining fluorine pneumatic diaphragm pump, stainless steel pneumatic diaphragm pump, cast iron pneumatic diaphragm pump, aluminum pneumatic diaphragm pump , Engineering plastic pneumatic diaphragm pump, GW pipe sewage pump, LW vertical sewage pump, ZWL direct self-suction sewage pump, ISG vertical pipe pump, ISW horizontal pipe centrifugal pump, CQB heavy duty stainless steel magnetic pump, CQB-G high temperature Stainless steel magnetic pump, G screw pump | single screw pump | thick pump, JMZ, FMZ self-priming pump suction pump, ZX water pump, ISWH, ISWHD horizontal stainless steel chemical pipeline pump, QJ deep well pump, KCB , 2CY gear pump, PBG shield pipe pump, CDLF stainless steel multistage stamping centrifugal pump, LG, LG-B high-rise multi-stage centrifugal pump, S, SH in the open double suction centrifugal pump, DL, DLR vertical multistage centrifugal pump , ISWR, ISWRD horizontal hot water pipeline pump, GDL multi-stage pipeline pump, lined fluorine electric diaphragm pump, tear submersible sewage pump, Stir movable sewage pump, ZW self-priming non-clogging sewage pump, WQ type submersible non-clogging sewage pump, FPZ, PVZ corrosion resistant self-priming pump.