1.Air intrusion: After the air enters the hydraulic system, the volume is large in the low pressure area, it is compressed when entering the high pressure area, and the volume is suddenly reduced, and when it flows into the low pressure area, the volume is suddenly increased, resulting in the bubble "explosion" and noise.

Solution: Set the exhaust device on the hydraulic cylinder, or let the actuator exhaust several times in a rapid full stroke after driving.

2 .Hydraulic pump or hydraulic motor quality problems: hydraulic pump or hydraulic motor quality is not good, such as accuracy does not meet the technical requirements, pressure and flow fluctuations, trapped oil phenomenon is not eliminated, seal is not good or bearing quality is poor, will lead to noise. In addition, in the process of use, due to parts wear, excessive clearance, insufficient flow, pressure fluctuations and other reasons, will also cause noise.

The solution:

- Choose a good quality hydraulic pump or hydraulic motor, and perform regular repair and maintenance. For example, for the problem of low gear accuracy, the gear should be ground to meet the contact surface requirements;

- For the trapped oil phenomenon of the vane pump, the triangle groove of the oil distribution pan should be corrected to eliminate the trapped oil;

- If the axial clearance of the hydraulic pump is too large, resulting in insufficient oil delivery, it should be repaired to make the axial clearance within the allowable range;

- If the hydraulic pump is found to be improperly selected, it should be replaced immediately.

3.Improper adjustment of reversing valve: improper adjustment of reversing valve, spool moving too fast, will cause reversing impact, noise and vibration. In addition, when the spool frequency is similar to the pulsation frequency of the hydraulic pump oil transmission rate or other vibration source frequency, vibration and noise will also be caused.

Solution: For the hydraulic reversing valve, the throttle element in the control oil circuit should be adjusted to make the reversing smooth without impact. Vibration and noise can be prevented by changing the natural frequency of the pipeline system, changing the position of the control valve or adding an accumulator.

4.The relief valve is unstable: the spool is not properly fitted with the valve hole, the contact between the cone valve and the seat is stuck with dirt, the damping hole is blocked, the spring is crooked or fails, and other reasons will make the spool stuck or move ineffectively in the valve hole, resulting in system pressure fluctuation and noise.

Solution: pay attention to cleaning and dredging the damping hole. Check the relief valve, if any damage should be repaired or replaced in time.