The piston is located at the end of the piston rod and acts as a movable barrier in the compressor cylinder. It is generally made from materials such as aluminum or cast iron and has a hollow center. Small-diameter high-pressure cylinders may be provided with a combined piston and rod machined from a single piece of bar stock.
To reduce friction and improve compression efficiency, the piston will be provided with segmented compression rings as shown in Figure 11 -11. To prevent piston-to-bore contact, the piston may also be provided with removable wear bands that are in continuous contact with the cylinder wall. The compression rings and wear bands are replaced at regular intervals and typically made from soft materials such as brass, Micarta, Teflon, and the newer thermoplastics.