# Adsorption (desiccant) dryer

An adsorption (desiccant) dryer removes water vapour from compressed air by passing it through a desiccant that holds the moisture, and it reaches much lower pressure dew points than a refrigeration dryer.

The desiccant has to be dried again to keep working, so the medical air dryers described in HTM 02-01 (2026) have two columns: one dries the compressed air while the other is regenerated with dry air from the active column, and a second complete dryer assembly keeps the supply going. Dryness is stated as [pressure dew point](https://library.ultracontrolo.com/glossary/pressure-dew-point/), the temperature at which water would start to condense at working pressure, and ISO 8573-1 classes compressed air by its water content among other contaminants.

The ULTRADRY adsorption dryer gives a pressure dew point of −40 °C to −70 °C, with a coalescing filter at the inlet, a dust filter at the outlet and the desiccant in replaceable cartridges. Its table values are given at −40 °C pressure dew point with inlet air at 35 °C and 7 bar g, and it works from 4 to 16 bar g. ULTRADRY is an option on ULTRAAR ME medical air plants, and the ACIH hospital industrial air system can take adsorption dryers for dew points of −20 °C or −40 °C.

## Sources

- [HTM 02-01 (2026) Part A, paragraphs 7.64 to 7.67 (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)
- [ISO 8573-1:2010, Compressed air, purity classes (ISO summary)](https://www.iso.org/standard/46418.html)
- [ULTRADRY datasheet, p. 2 and p. 3](https://www.ultracontrolo.com/products/ultradry)
- [ULTRAAR ME datasheet, p. 4](https://www.ultracontrolo.com/products/ultraar-me)
- [ACIH datasheet, p. 7](https://www.ultracontrolo.com/products/acih)
- [Ultra Controlo, Medical gas answers: refrigeration vs adsorption dryer](https://www.ultracontrolo.com/medical-gas-answers)

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