# Coalescing filter

The US Department of Energy compressed air sourcebook lists coalescing filters as the filters that remove lubricant and moisture; for hospital technical air, Portugal’s ACSS ET 08/2010 (V.2025) puts one before each dryer to remove solid particles and water and oil aerosols, and NHS England’s HTM 02-01 (2026) asks for automatic drainage traps on them.

The sourcebook (third edition) recommends a coalescing-type filter before a desiccant dryer to prevent fouling of the desiccant bed, and names it, or an air/lubricant separator, as the means of removing the lubricant aerosols left after the sump/separator of a lubricant-injected rotary screw compressor. WHO’s Foundations of medical oxygen systems (2023) shows a 0.1 micron coalescing filter in the filtration assembly of a typical PSA plant. NHS England guidance, HTM 02-01 (2026), asks for electrically operated automatic drainage traps on coalescing filters, as on after-coolers, receivers and separators.

For hospital technical air, the Portuguese ACSS ET 08/2010 (V.2025) puts a coalescing filter immediately before each dryer, typically filtering particles down to 1 µm, and a high efficiency coalescing filter after the dryer and dry receiver, with a particle removal efficiency of 0.01 µm and oil penetration below 0.01 mg/m³. It notes that oil-free compressors can remove the need for high efficiency coalescing filters for oil removal.

In Ultra Controlo equipment, the [ULTRADRY](https://library.ultracontrolo.com/products/ultradry/) adsorption dryer has a coalescing filter at the inlet, and the [ULTRAMED](https://library.ultracontrolo.com/products/ultramed/) treatment station has a high efficiency coalescing filter for removing water, oil and aerosols.

## Sources

- [US Department of Energy, Improving Compressed Air System Performance: A Sourcebook for Industry, third edition](https://www.energy.gov/sites/prod/files/2016/03/f30/Improving%20Compressed%20Air%20Sourcebook%20version%203.pdf)
- [WHO, Foundations of medical oxygen systems (17 February 2023), Fig. 2.2](https://iris.who.int/server/api/core/bitstreams/4ad6f5fd-089e-4142-8439-b64e98d816d8/content)
- [HTM 02-01 (2026) Part A, paragraph 7.56 (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)
- [ACSS ET 08/2010 V.2025, Especificações técnicas para ar comprimido técnico em edifícios hospitalares, sections 4.2.4.3 and 4.2.7](https://www.acss.min-saude.pt/wp-content/uploads/2016/10/ET-08_2010_V.2025_VF.pdf)
- [ULTRADRY datasheet, p. 2](https://www.ultracontrolo.com/products/ultradry)
- [ULTRAMED datasheet, p. 3](https://www.ultracontrolo.com/products/ultramed)

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