1. the joint surface of hydraulic components may be damaged during assembly and maintenance of vertical roller mill , or the paper pad is damaged by pressure oil, or there is flatness error in the joint surface during the repair or the screw of the joint is not tightened, etc. all may cause the joint surface leakage; If the operation is barbaric and excessive force, especially the knock on the cylinder block and sealing flange with copper rod, the parts will be deformed and leakage will be caused.

2. the seal is made of oil resistant rubber and other materials. The system leakage will be caused by aging, cracking and damage caused by long-term use. If the parts are damaged by collision during the working process, the sealing elements will be scratched, resulting in leakage. Or the system pressure is too high, which causes the seal failure to cause leakage.

3. the increase of the clearance of the spool valve in the hydraulic control valve results in an increase in leakage.