During the maintenance of engineering vehicles, we usually detect that there are some cellular cavities inside the hydraulic cylinder or at the surface of piston, piston rod. These cavities are caused by cavitation corrosion. Hydraulic cylinder cavitation could lead to burning of bearing rings and seal rings, and finally result in cylinder leak. In addition, cavitation, coupled with other types of corrosion, will greatly accelerate the corrosion of main hydraulic cylinder parts, thus significantly affecting the operation of the engineering vehicles like road rollers, loaders, and excavators. 
1. What Causes Cavitation? 
(1) Analysis of Cavitation 
Cavitation is the formation of vapor bubbles of a liquid in a region where the pressure of the liquid falls below its vapor pressure. When the cavitation bubbles collapse, they force energetic liquid into very small volumes, thus creating spots of high temperature and emitting shock waves. The highly localized collapses can produce great wear on components of hydraulic cylinders. 
(2) Cavitation Caused by Unqualified Hydraulic Oil 
High quality hydraulic oil can effectively prevent cavitation. Bubbles can be easily formed in oil with poor antifoaming ability, thereby resulting in cavitation. In addition, if the frequency of oil pressure change is too high, air bubble formation and collapse can also be largely accelerated. Moreover, overheated oil will also increase the possibility of cavitation.
(3) Cavitation Due to Improper Manufacture and Maintenance 
In the assembly or maintenance, air in hydraulic system is not discharged, which could cause cavitation under high temperature, high pressure conditions. 
(4) Cavitation Resulting from Poor Quality Coolant 
The coolant which contains corrosive medium like acid radical cation and oxidant is liable to chemical, electrochemical corrosion, thereby accelerating the speed of cavitation. 

2. How to Prevent Cavitation? 
Although there are many factors could cause cavitation, cavitation can also be avoided if we take effective measures to prevent it. 
(1) Use High Quality Hydraulic Oil 
Choose high quality hydraulic oil according to the related oil standard, because qualified oil can effectively prevent the formation of air bubble. Keep the hydraulic system as clean as possible, and regularly inspect the oil quality, oil level and oil color. Whenever water bubbles or foams occur in the hydraulic oil, please work to find the air source and then eliminate it. 
(2) Prevent the Oil Temperature from Being too High so as to Reduce Hydraulic Shock 
Reasonable design of the cooling system is key to maintaining normal temperature of hydraulic oil. In addition, smoothly operate hydraulic joystick, distribution valve and thrust lever, in order to minimize hydraulic oil's impact on the hydraulic components. Furthermore, timely maintain the cooling system so as to keep its temperature within certain boundaries, thus reducing the energy caused by the collapse of air bubbles. 
(3) Maintain the Normal Clearance between Joint Surfaces of Hydraulic Components
When manufacture or repair main components of the hydraulic cylinder (like cylinder block, piston rod), please assemble them according to the lower tolerance limit of mounting dimensions, which can greatly reduce cavitation. If cavitation occurs in hydraulic components, utilize metallographic sandpaper polishing technique to remove cavitation pitting and surface carbon deposit. 
(4) Pay Attention to Air Discharge during Maintenance 
After maintenance, the hydraulic system should be operated for a while so that the hydraulic oil in the system can fully circulate. If necessary, disassemble the oil inlet pipe or return pipe so as to let the oil spill out of it, thus achieving air discharge of single cylinder.