Does a PSA oxygen plant need oil-free compressors?

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

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 and oil-free or oil-lubricated compressors for medical air.