# How much compressed air does a PSA generator need?

**How much compressed air does a PSA oxygen generator consume, by generator size and purity setting?**

A PSA generator's compressed air need depends on its size and purity setting: the ULTRACON datasheet lists 3.5 Nm³/h of air for 0.32 Nm³/h of 93% oxygen in the smallest generator and 1,258 Nm³/h of air for 111.4 Nm³/h in the largest, the ULTRACON 14D.

The ULTRACON is the PSA oxygen generator used in ULTRAOX plants. It produces oxygen from compressed air fed to the unit: two columns go through a cyclic sequence of high and low pressure steps, retaining contaminants in the high pressure step and releasing them in the low pressure step. Its datasheet gives, for every size, the oxygen delivered and the compressed air consumed at two purity settings, which are the flows the plant's compressors must supply.

## ULTRACON oxygen output and air consumption

| ULTRACON model | Oxygen at 93% (Nm³/h) | Air at 93% (Nm³/h) | Oxygen at 95% (Nm³/h) | Air at 95% (Nm³/h) |
|---|---|---|---|---|
| 1 | 0.32 | 3.5 | 0.3 | 3.5 |
| 2 | 0.78 | 8.6 | 0.7 | 8.5 |
| 3 | 1.1 | 12 | 0.9 | 12 |
| 4 | 3.1 | 35 | 2.5 | 32 |
| 5 | 4.6 | 52 | 3.8 | 47 |
| 6 | 6.5 | 74 | 5.3 | 66 |
| 7 | 8 | 90 | 6.5 | 81 |
| 8 | 9.5 | 108 | 7.8 | 97 |
| 9 | 12.4 | 141 | 10.1 | 126 |
| 10 | 18.2 | 206 | 14.8 | 185 |
| 11 | 26.2 | 296 | 21.3 | 266 |
| 12 | 36.5 | 413 | 29.7 | 371 |
| 13 | 43.5 | 492 | 35.3 | 442 |
| 11D | 52 | 592 | 42.6 | 532 |
| 14 | 55.7 | 629 | 45.2 | 566 |
| 12D | 73 | 826 | 59.4 | 742 |
| 15 | 82.65 | 934 | 67.16 | 839.5 |
| 14D | 111.4 | 1,258 | 90.4 | 1,132 |

Source: ULTRACON datasheet, p. 3. The datasheet also gives the oxygen flows in Nl/min and SCFH.

## Reading the table

- Purity changes the result. Every generator in the table delivers less oxygen at 95% than at 93%, and the Global Fund purity note (3 April 2024) gives a similar example: equipment producing 20 Nm³/h at 93% (±3%) would produce 18 Nm³/h set to 95% (±1%).
- Pressure. The ULTRAOX SC and ST model tables give an inlet pressure of 7.5 bar for the compressed air and an oxygen outlet pressure of 6 bar on every model.
- Plant configuration. ULTRAOX plants combine one or more compressors with one or more ULTRACON concentrators; the compressors switch and the generators start in cascade to keep a continuous supply (ULTRAOX SC and ST datasheets).
- Energy. WHO's Foundations of medical oxygen systems (2023) says the energy efficiency of a PSA plant is largely determined by the feed air compressor; see [how much electricity a PSA plant uses](https://library.ultracontrolo.com/answers/how-much-electricity-does-a-psa-plant-use/).

## What other guidance says

WHO (2023) describes oxygen concentration as beginning with the compression of ambient air. The 2020 WHO interim specification for PSA plants (superseded by WHO's technical specifications of 31 December 2024), issued on 8 June 2020, which stated that it would expire two years after publication, asked for a feed air compressor of at least 750 kPa (7.5 bar) and an external air dryer sized to manage the compressor output. PATH and CHAI (2021) note that, depending on the manufacturer, a compressed air surge tank, an air compressor and a filter or dryer may be required, and that PSA manufacturers commonly provide recommended models or specifications for this equipment as a package. For how the compressor itself is chosen, see [how the air compressor for a PSA plant is sized](https://library.ultracontrolo.com/answers/how-is-the-air-compressor-for-a-psa-plant-sized/).

### Does a generator use more air at 95% purity?

The ULTRACON table lists the same or less air at 95% but less oxygen: the ULTRACON 10 uses 185 Nm³/h of air for 14.8 Nm³/h at 95%, against 206 Nm³/h of air for 18.2 Nm³/h at 93%.

### At what pressure must the compressed air arrive?

The ULTRAOX SC and ST model tables list 7.5 bar at the inlet for every model, with oxygen delivered at 6 bar.

## Sources

- [ULTRACON datasheet, p. 2 and p. 3 (model table)](https://www.ultracontrolo.com/products/ultracon)
- [ULTRAOX SC datasheet, p. 2 and p. 5 (model table)](https://www.ultracontrolo.com/products/ultraox)
- [ULTRAOX ST datasheet, p. 2 and p. 5 (model table)](https://www.ultracontrolo.com/products/ultraox-st)
- [Global Fund / Build Health International, Briefing Note: PSA Plant Oxygen Purity (3 April 2024)](https://resources.theglobalfund.org/media/lenpqaoa/cr_c19rm-psa-oxygen-purity_technical-briefing-note_en.pdf)
- [WHO, Foundations of medical oxygen systems (17 February 2023)](https://iris.who.int/server/api/core/bitstreams/4ad6f5fd-089e-4142-8439-b64e98d816d8/content)
- [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)
- [PATH and CHAI, Oxygen Generation and Storage: Pressure/Vacuum Swing Adsorption Plant (July 2021)](https://media.path.org/documents/O2_generation_and_storage_PSA_VSA_v1.pdf)
- [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/how-much-compressed-air-does-a-psa-generator-need/