Reasons why you can't push in when switching screen changer

There are four possible of screen changer:

1. There is a large foreign body stuck in the net board.

2. The oil pump of the hydraulic station is worn out and broken.

3. The oil seal of the propelling cylinder is broken, causing leakage and powerlessness.

4. There is not enough hydraulic oil in the hydraulic station.

Please check and solve!