1. should adjust the coaxiality of the piston and the piston rod.
2. the machining accuracy of the inner wall of the cylinder and the surface of the piston rod are adjusted to the appropriate range.
3. if it is caused by the material of the seal, just replace it.
4. add a venting device in the hydraulic cylinder to discharge air.
5. should adjust the gap between the piston and cylinder, piston rod and guide sleeve inside the hydraulic cylinder.