Check whether enough hydraulic oil is filled in the oil tank. The common medium-sized CNC straightening machines on the market are filled with 46# anti-wear hydraulic oil, and the filling amount ranges from 25 to 50 liters. It is generally observed from the refueling filter screen, it is better to fill the hydraulic oil to the filter screen.
To determine whether the hydraulic system has air intake, one is to observe whether there are bubbles in the hydraulic oil entering the gear pump from the oil intake pipe (see Figure 1). The second is to take out the filter screen from the fuel tank to observe whether the hydraulic oil has air bubbles after running for a few minutes.
Remove the solenoid valve spool and rub the spool with gauze to make the spool move normally.