# Does a PSA oxygen plant need oil-free compressors?

**Does the compressor feeding a PSA oxygen plant have to be oil-free?**

Not as a universal rule: the WHO interim technical specifications for PSA oxygen plants (2020, superseded in 2024) accepted a feed air compressor that is oil-free or a filtered oil-injected or oil-lubricated rotary screw type. What is fixed is the quality of the oxygen, and the pharmacopoeia limits include a maximum oil content.

## What the specifications require

The WHO interim specifications for PSA oxygen plants (June 2020) described the feed air compressor as either oil-free or a filtered oil-injected or oil-lubricated rotary screw type, delivering at least 750 kPa (7.5 bar). The limits sit on the product: the International Pharmacopoeia (13th edition, 2025) allows at most 0.1 mg/m3 of oil and 67 ppm of water in Oxygen 93%, and the European Pharmacopoeia monograph 2455 defines Oxygen 93 quality as delivered into the pipeline. Whatever the compressor, the oxygen leaving the plant has to meet these limits.

## What NHS England guidance adds

HTM 02-01 (2026) says compressors for PSA systems should comply with its medical air requirements, and that the medical air plant itself should not be used for the PSA. For medical air compressors it says oil-free machines should be considered as replacements for oil-filled ones, because they reduce filtration requirements and the risk of oil contamination, while oil-lubricated compressors may be used if suitable arrangements ensure the air-quality specification is met.

Oil-lubricated screw compressors are common in practice: a USAID operating procedure for PSA plants, written for hospitals in India, describes the lubricated screw compressor as the type typically used, and the Global Fund daily checklist for PSA operators asks whether the compressor oil level is correct and whether there are signs of oil leakage.

## How ULTRAOX plants are configured

| Plant | Compressor | Oil in the compression |
|---|---|---|
| ULTRAOX SC | One or more ULTRACECO compressors, described in the datasheet as oil-less, Class 0 | None; the datasheet lists oil in fluid phase as exempt |
| ULTRAOX ST | One or more ULTRASCREW rotary screw compressors | Oil injected, per the ULTRASCREW datasheet; not an oil-free plant |

Both deliver 94% (±1%) oxygen, with oxygen quality according to the European Pharmacopoeia stated in their datasheets. The ULTRAOX datasheet lists the air treatment ahead of the generator: a water separator with electronic drain, high efficiency micro and sub-micro filters and an activated carbon filter. On maintenance, the ULTRAOX SC datasheet states one service at 10,000 hours. See also [Class 0](https://library.ultracontrolo.com/glossary/class-0/) and oil-free or oil-lubricated compressors for medical air.

### Is the ULTRAOX ST oil-free?

No. It uses ULTRASCREW compressors, which are oil-injected rotary screw machines; the oil-free ULTRAOX version is the SC, with oil-less ULTRACECO compressors.

### What extra checks does an oil-lubricated PSA compressor need?

The Global Fund daily checklist asks operators to confirm the compressor oil level is at the manufacturer's level and that there is no sign of oil leakage.

## Sources

- [WHO, Technical specifications for PSA oxygen plants, interim guidance (8 June 2020)](https://www.who.int/publications/i/item/WHO-2019-nCoV-PSA_Specifications-2020.1)
- [The International Pharmacopoeia, 13th edition (2025), Medicinal oxygen](https://digicollections.net/phint/202502/index.html#d/b.6.1.226)
- [EDQM, monograph history, Oxygen (93 per cent) 2455](https://extranet.edqm.eu/4DLink1/Web_mono_hist?2455)
- [NHS England, HTM 02-01 Part A (2026), paragraphs 6.117, 7.34 and 7.35](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)
- [USAID RISE, SOP: PSA Plant Operations and Preventive Maintenance (March 2022)](https://media.path.org/documents/SOP_on_PSA_Plant_USAID_RISE_04032022_F7fUBr6.pdf)
- [Global Fund / Build Health International, PSA plant Daily Maintenance Checklist (2025)](https://resources.theglobalfund.org/media/xbanfgrc/cr_c19rm-psa-plant-daily-maintenance_checklist_en.pdf)
- [ULTRAOX SC datasheet, p. 2 and p. 3; ULTRAOX datasheet 2022, p. 16](https://www.ultracontrolo.com/ultraox)
- [ULTRAOX ST datasheet, p. 2 and p. 3](https://www.ultracontrolo.com/products/ultraox-st)
- [ULTRASCREW datasheet, p. 2](https://www.ultracontrolo.com/products/ultrascrew)
- [WHO, Technical specifications for health facility based medical oxygen systems (31 December 2024), note on the oxygen generator plant specification (supersedes the 2020 interim PSA specifications)](https://iris.who.int/server/api/core/bitstreams/ff437601-add3-44c8-8149-b85f0cdb2b52/content)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/does-a-psa-plant-need-oil-free-compressors/