# Piston (reciprocating) compressor

In the US Department of Energy compressed air sourcebook, a piston, or reciprocating, compressor is one whose compressing element is a piston moving back and forth in a cylinder; driven through a crankshaft and connecting rod, the piston reduces the volume the air occupies, compressing it to a higher pressure.

The sourcebook (third edition) separates single-acting compressors, in which compression takes place on the top side of the piston, from double-acting ones, which use both sides of the piston. For single-acting designs it describes lubricated versions with compression and lubricant-control piston rings, lubricant-free designs that keep lubricant out of the compression chamber, and lubricant-less, or oil-less, designs that also have no lubricant in the crankcase.

NHS England guidance, HTM 02-01 (2026), lists reciprocating compressors among the most common types for medical air and says they may be of the oil-lubricated, carbon-ring, PTFE-ring or diaphragm-sealed type. Because PTFE rings and lubricating oils could decompose at high temperatures to form toxic products, it says this can be countered by a temperature sensor on the cylinder head or compressor output, with controls that cut off the power if excessive temperatures are sensed.

ULTRACECO ESW is the Ultra Controlo oil-free piston compressor range, with QuAir 3 touch-screen controllers, a first maintenance at 10,000 hours and a belt that can be changed in 5 minutes without disassembling the compressor. [ULTRAAR ESW](https://library.ultracontrolo.com/products/ultraar-esw/) medical air plants use these oil-less piston compressors and are designed with 1 to 8 compressors, among other configurations.

## Sources

- [US Department of Energy, Improving Compressed Air System Performance: A Sourcebook for Industry, third edition, Positive Displacement Compressors and Appendix A](https://www.energy.gov/sites/prod/files/2016/03/f30/Improving%20Compressed%20Air%20Sourcebook%20version%203.pdf)
- [HTM 02-01 (2026) Part A, paragraphs 7.31, 7.36 and 7.38 (NHS England)](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-a-design-installation-validation-verification-aug-2026.pdf)
- [ULTRACECO ESW datasheet, p. 2 and p. 3](https://www.ultracontrolo.com/products/ultraceco-esw)
- [ULTRAAR ESW datasheet, p. 3 and p. 4](https://www.ultracontrolo.com/products/ultraar-esw)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/glossary/piston-compressor/