1, may be the hydraulic pump without pressure. Solution: Check to see if the pressure is low, you can try to control the large overflow valve;
2, It may be blocked by the Filter. Solution: Check the hydraulic pump suction port filter, or the system filter net, remove rubbish;
3, may be due to the problem of the seal string Oil. Solution: Check the piston seal ring of the action cylinder to ensure the sealing ring Intact.