The pump is an energy conversion device that converts the rotational mechanical energy of the motor into hydraulic energy output. Hydraulic pumps work on the principle of changing the sealing volume, so they are usually called positive displacement hydraulic pumps. Figure 2-1 shows the working principle of a single-piston hydraulic pump. In the figure, the piston 2 is installed in A sealing volume a is formed in the cylinder block 3 , and the plunger is constantly pressed against the eccentric 1 under the action of the tension spring 4 . The prime mover drives the eccentric wheel 1 to rotate to make the plunger 2 reciproe, so that the size of the sealing volume a is periodically replaced and changed. When a increases from small to large, some vacuum is formed, so that under the effect of atmospheric pressure, the oil in the oil tank will open the check valve 6 through the oil suction pipe and enter the oil cavity a to complete the oil absorption;