During operation, the power machine drives the main shaft and the crank that is fixed thereon by a transmission component such as a belt, a transmission shaft, and a gear. When the crank rotates counterclockwise from the horizontal position from left to right, the piston moves to the power end, the pressure in the liquid cylinder gradually decreases and a vacuum is formed, and the liquid in the suction pool is under the action of the liquid surface pressure, and the suction valve is opened to enter the liquid cylinder. Until the piston moves to the right stop. This working process is called the suction process of the pump.

After the crank completes the above suction process, it continues to rotate counterclockwise. At this time, the piston starts to move toward the hydraulic end (left side in the figure), and the liquid in the cylinder is squeezed. The pressure rises, the suction valve closes, and the discharge valve is closed. Top open, liquid enters the discharge pipe until the piston moves to the left stop. This process is called the pump discharge process. As the power machine continues to operate, the reciprocating pump continuously repeats the process of inhaling and discharging, and the liquid in the suction pool is continuously sent to the bottom of the well through the discharge pipe.

The distance the piston moves in the cylinder is called the stroke length of the piston; the number of reciprocations of the piston per minute is called the stroke of the piston.