Excavator overflow pneumatic valve the reasons for the noise

the overflow pneumatic valve is easy produce high-frequency noise, mainly is the forerunner of pneumatic valve performance is not stable, namely as the forerunner of pneumatic valve cavity pressure high-frequency oscillation caused by air before the vibration and noise. The main reason is:
( The oil mixed with air, in front of the pilot pneumatic valve cavity formation of cavitation caused the high frequency noise. At this point, should be timely to do back into the air and prevent the outside air.
( Needle pneumatic valve in use process due to the frequent open excessive wear, make needle pneumatic valve cone cannot be closed with the pneumatic valve seat, the pilot flow instability, produce pressure fluctuation caused by noise, should be timely repair or replacement at this time.
( The forerunner of pneumatic valve caused by deformation of spring fatigue its regulating function is not stable, makes the pressure fluctuations caused big noise and springs should be changed at this time.