How is air compressed in a small compressor?

• A. Rotary vane action
• B. Screw compression
• C. Membrane compression
• D. Piston movement

Answer: (D)

Air is typically compressed in a small compressor by a piston moving inside a cylinder. When the piston moves down, air is drawn in through an intake valve. As the piston moves up, the volume inside the cylinder shrinks, squeezing the air and raising its pressure. The compressed air is then pushed out through a discharge valve into the storage tank or delivery line. This reciprocating piston setup is simple, reliable, and cost-effective for small units, which is why it’s the common method at this size.

Other designs exist, but they use different mechanisms: rotary vane uses a spinning rotor with sliding vanes to trap and compress air; screw compression uses two intermeshing screws to trap and compress air between them; membrane compression relies on a flexible membrane that bulges to increase pressure. These approaches are used in other types or sizes of compressors, but for compact, basic systems, the piston-based method is the practical choice.