During maintenance of hydraulic pump, the fault causes are found from the following three points.

(1) Checking the inner leakage of movable arm oil cylinder. The simplest way is to raise the arm and see if it has a distinct free fall. If the fall is obvious, removing the oil cylinder and checking. If the sealing ring is worn, it should be replaced.

(2) Checking the control valve. First, cleanung the safety valve and checking whether the spool is worn. If it is worn, it should be replaced. If there is no change after the installation of the safety valve, checking the wear of the operating valve spool again, and its clearance limit is generally 0.06mm. If it is worn and serious, it should be replaced.

(3) Measuring the pressure of the hydraulic pump. If the pressure is too low, adjusting it. If the pressure is still too low, it declared that the hydraulic pump is worn seriously.