When the piston moves from the top dead center to the bottom dead center of the cylinder, the volume inside the cylinder increases and the pressure drops. When the pressure inside the cylinder falls below the ambient atmospheric pressure, driven by the pressure difference between the inside and outside of the cylinder, the outside air overcomes the tension of the spring to push open the intake valve and enter the cylinder (at this moment, the discharge valve is closed). When the piston reaches the bottom dead center, the cylinder is filled with air whose pressure is equal to the ambient atmospheric pressure. As the pressure inside and outside the cylinder is balanced, the valve spring closes the intake valve by bouncing it back, thus completing the intake stroke.

When the piston moves from the bottom dead center to the top dead center, both the intake valve and the discharge valve are closed, and the air inside the cylinder is compressed. As the piston moves upward, the volume of the cylinder continues to decrease, and the pressure of the compressed air rises accordingly. This process is called the compression stroke.

When the pressure of the compressed air exceeds the combined force of the valve spring tension and the pressure inside the discharge pipe, the discharge valve is pushed open, and the compressed air is discharged through the discharge pipe until the piston reaches the top dead center. At this point, most of the compressed air inside the cylinder has been discharged, causing the air pressure to drop sharply. The discharge valve then closes the cylinder again under the tension of its spring. This process is known as the discharge stroke.

When the piston moves from the top dead center to the bottom dead center again, fresh air is drawn into the cylinder, initiating the next intake stroke. In this way, the reciprocating air compressor operates in a continuous cycle of intake, compression, and discharge.