Supply Air in Suction
The method of air replenishment can not prevent cavitation cavitation, but proper air replenishment can reduce the damage to the side wall of the flow channel caused by the hole fracture, and the air replenished is like a sponge to protect the side wall of the flow channel. This method is widely used in hydraulic turbines, but it is very rare to supply air to the pump due to the difficulty in mastering the amount of air supply. Some people have studied the cavitation of the air make-up water-proof pump and achieved some results. But at the same time, it is pointed out that the air make-up prevention and control of the cavitation of the split case pump is highly technical. Only when the air make-up flow rate, air make-up position and air make-up method are appropriate, can good results be achieved. Otherwise, the flow, head and efficiency of the pump will be greatly reduced, resulting in adverse consequences.
Use of Anti Cavitation Materials
There are obvious differences in the anti cavitation ability of different materials. There are many factors that affect the anti erosion ability of materials, usually the materials with high hardness and high elasticity have strong anti erosion ability. Low carbon chromium nickel alloy steel is recommended abroad as a kind of hydraulic machinery material working in cavitation state, which has better anti erosion performance. It is also effective to use anti cavitation materials when cavitation can not be avoided. Compared with cast iron and copper, the original cast steel is replaced by stainless steel. Cavitation erosion will be multiplied. It has been proved that the cavitation phenomenon is very prominent in the split case pump running in the low temperature heating system of our company. Replacing the flow passage parts of the materials resistant to cavitation is the easiest way to solve or reduce the cavitation.
Impeller Protection Layer
The coating method of impeller is commonly used. The coating method of nonmetal coating is epoxy resin, nylon powder, polyurethane, etc. In addition, the method of overlaying or spraying alloy on the surface of flow passage has also achieved certain effect on cavitation damage, such as stainless steel electrode overlaying, stainless steel plate inlaying welding repair, alloy powder spray welding. Compared with several methods of non-metallic and alloy (including stainless steel), the non-metallic coating is economical, but the coating often falls off. The experience should be summarized in the construction of Suran. Alloy surfacing is usually carried out by users themselves. The effect of alloy powder spray welding is good, but the cost is high, and some places may not be carried out. There are many examples about protection layer. For example, the blade treated by metal alloy powder spray welding in a pumping station has achieved good anti cavitation effect and the service life can be extended.
Trim Impeller head
Trimming the tip of impeller has obvious effect on reducing cavitation damage. The principle is to reduce the extrusion of the blade inlet and the speed of liquid flow at the blade inlet. The method is to thin the back of the blade head, and repair more near the front cover plate of the impeller.
There are application examples to reduce the cavitation damage of the pump, sometimes several methods need to be used at the same time. To sum up, in the installation process of centrifugal pump, in order to avoid cavitation as much as possible, several principles should be followed: the installation height of water pump must be lower than the allowable suction height of the pump; the suction pipeline should be short and straight, the pipe fittings should be as few as possible, the diameter of the suction pipe should not be less than the diameter of the suction port; there should be no gas accumulation at the reducer. In a word, during the operation of the centrifugal pump, pay attention to whether there is abnormal noise, observe whether the pressure gauge is normal, check the heating of the bearing and shaft seal regularly, and pay attention to whether there is abnormal leakage at the lubrication and shaft seal.