lifting force of the boom is insufficient or the turning force is insufficient. It is mainly because of improper safety valve adjustment and low pressure of hydraulic system, resulting in insufficient lifting force of boom or insufficient bucket force; blockage of suction pipe and oil filter makes the oil circuit not smooth, resulting in insufficient lifting force of boom or insufficient turning bucket force; Oil pump, cylinder, pipeline leakage and other reasons can also cause the boom lifting force is insufficient or the bucket force is insufficient; Multi-way valve excessive wear, valve stem and valve body with clearance exceeds the specified value so that the arm lifting force or insufficient bucket force.