Pump sucking air or damage; oil pump for pressurization of the core components of the whole system, the whole system is pressurized by pump; so the pump suck air or damage, pressures on the system are enormous. General pump suction or damaged, we will see lots of bubbles in the hydraulic oil, or abnormal noise. The most direct method is to use a pressure gauge directly connected to oil pump inspection (this method requires auxiliary components).
Solution: replace or repair oil pump.
Hydraulic valve leak or damaged; hydraulic system in the any of leak will effect to pressure of established; which hydraulic valve leaked most difficult found, General this leaked most for internal leaked eye hard observation to; has a simple of method does not necessarily has associate but is effective, is put Shang table rose to highest Hou shut machine, look table whether will has fell, as has is proved system has leaked discharge other of joint, external wrote slightly teeth on can roughly discriminant hydraulic valve whether has leaked of situation.
Solution: replace the hydraulic valve.