# Oil-injected compressor

In the US Department of Energy compressed air sourcebook, an oil-injected (lubricant-injected) rotary screw compressor injects lubricant into the compression chamber, where it lubricates the rotors and bearings, removes the heat of compression and seals the clearances, and the lubricant is then separated from the compressed air.

In the sourcebook (third edition), the mixture of compressed air and injected lubricant leaving the air end passes to a sump/separator, where changes of direction and velocity remove most of the liquid; an air/lubricant separator or a coalescing filter then removes the remaining aerosols, leaving a lubricant carry-over usually in the range of 2 to 5 ppm.

For medical air, NHS England guidance, HTM 02-01 (2026), accepts oil-lubricated compressors provided suitable arrangements ensure that its air-quality specification is fulfilled, says a suitable means of separating oil from condensate is essential, and says oil-free compressors should be considered as replacements for oil-filled ones because they reduce filtration requirements and minimise the risk of oil contamination. The EDQM history note of Ph. Eur. 1238, Air, medicinal, records that from Supplement 6.3 oil was controlled with oil detector tubes, a test it describes as only relevant when the gas is produced using an oil-lubricated compressor.

[ULTRASCREW](https://library.ultracontrolo.com/products/ultrascrew/) is the Ultra Controlo oil-injected rotary screw compressor range. It feeds the ULTRAOX ST oxygen plant, so the ST is not oil-free, while the ULTRAOX SC uses oil-less ULTRACECO compressors.

## Sources

- [US Department of Energy, Improving Compressed Air System Performance: A Sourcebook for Industry, third edition, Lubricant-Injected Rotary Screw Compressors](https://www.energy.gov/sites/prod/files/2016/03/f30/Improving%20Compressed%20Air%20Sourcebook%20version%203.pdf)
- [HTM 02-01 (2026) Part A, paragraphs 7.34, 7.35 and 7.42 (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)
- [EDQM, Ph. Eur. monograph 1238 Air, medicinal: history (oil test)](https://extranet.edqm.eu/4DLink1/Web_mono_hist?1238)
- [ULTRASCREW datasheet, p. 2](https://www.ultracontrolo.com/products/ultrascrew)
- [ULTRAOX ST datasheet, p. 2](https://www.ultracontrolo.com/products/ultraox-st)
- [ULTRAOX SC datasheet, p. 2](https://www.ultracontrolo.com/products/ultraox)

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