# PSA vs VSA vs VPSA: which oxygen technology to choose?

PSA, VSA and VPSA plants all separate oxygen from air with zeolite and produce about 93% oxygen; they differ in how air moves through the sieve beds: an air compressor at several bar (PSA), a low-pressure lobe compressor that also exhausts the nitrogen (VSA), or a lobe compressor plus a vacuum pump (VPSA).

A Global Fund briefing note (March 2025) states that PSA, VPSA and VSA all produce oxygen of approximately 93% by separating it from the nitrogen in atmospheric air, and that the process is identical in all three: the systems differ in their pressure levels and equipment. The International Pharmacopoeia (2025) defines Oxygen 93% as oxygen produced from ambient air by PSA or VSA.

## How they compare

|  | PSA | VPSA | VSA |
|---|---|---|---|
| Air handling (Global Fund, 2025) | Air compressor at 4.5 to 7 bar, with an air dryer | Lobe compressor at about 0.5 bar gauge, plus a vacuum pump | One lobe compressor at about 0.7 bar gauge, also used to exhaust the nitrogen |
| Sieve bed tanks | Two (Global Fund, 2025) | Two (Global Fund, 2025) | Fewer adsorption vessels and valves than PSA (PATH and CHAI, 2021) |
| Oxygen to the pipeline | Leaves the generator at 3.5 to 5 bar, enough for wall outlets; no booster | Oil-free booster needed; a scroll compressor takes it to 5 bar | Oil-free booster needed; a scroll compressor takes it to 3 to 7 bar |
| Power (Global Fund) | Large plants can have high compressor in-rush currents | Lower average power than PSA | Lower average power than PSA, though savings may not appear in smaller plants; same peak power as PSA |
| Capital cost | Lower than VSA (PATH and CHAI, 2021; WHO, 2023) | WHO: a significant cost investment because of its complexity | WHO: about 15% above PSA, a margin that drops off above 100 Nm³/h; PATH and CHAI: a 10% to 20% premium |
| Watch-outs (Global Fund) | More filters to replace because of oil in the rotary screw compressor | Reports of low purity; extra compressors add failure points | Highly specialised, very expensive maintenance tools |

## What WHO and PATH add

WHO's Foundations of medical oxygen systems (February 2023) lists VSA advantages: an oil-free blower that lowers filtration needs and removes the risk of oil carry-over, higher efficiency in humid climates because no air dryer is needed, operation less affected by altitude, and sieve beds with a longer projected life. Because VSA output pressure is below common pipeline requirements, an oil-free booster is generally added. WHO describes VPSA as generally preferred for large-scale production, and notes that VSA availability for medical use is restricted by the low number of manufacturers, while PSA is more commonly available.

PATH and CHAI (July 2021) described VSA as more energy-efficient, with lower operating costs, and gave nominal flows of 0.5 to 150 Nm³/h for conventional PSA plants and 52 to 3,155 Nm³/h for VSA plants. Whatever the technology, they advised that the tender include robust technical and performance requirements based on the intended use and location.

## How to choose

The Global Fund recommendation is to buy the technology already common and working in the region: existing functioning plants mean local technicians and an established supply chain for spare parts. It warns that where VPSA or VSA plants are not common, spare parts and maintenance support may not be optimal, and notes that some manufacturers consider VPSA more appropriate for larger industrial applications.

## Where Ultra Controlo plants fit

ULTRAOX SC and ST hospital plants use PSA: compressors feed ULTRACON generators with two columns, delivering 94% (±1%) oxygen at 6 bar, with models from 0.32 to 164 m³/h per unit in the ULTRAOX ST table. ULTRAOX VSA is a separate industrial line: it delivers 75% to 95% oxygen at 50 kPa, higher pressures can be reached with an additional oxygen booster supplied on demand, and its table runs from 18 to 240 m³/h at 93%. See [industrial VSA plants](https://library.ultracontrolo.com/answers/industrial-oxygen-plant-vsa/).

### Can VSA oxygen be used in hospitals?

The International Pharmacopoeia includes VSA among the processes for Oxygen 93%, but WHO (2023) notes that few manufacturers market VSA for medical use; the Ultra Controlo VSA line is industrial.

### Does altitude favour VSA?

WHO (2023) says VSA operation is less affected by altitude, and PATH and CHAI (2021) said VSA can operate at higher altitudes without a reduction in performance.

### Why do VSA and VPSA plants need a booster?

Their oxygen leaves the generator at low pressure, below what wall outlets need, so the Global Fund note lists an additional oil-free oxygen booster compressor for distribution.

## Sources

- [Global Fund / Build Health International, Briefing Note: PSA, VPSA and VSA (4 March 2025)](https://resources.theglobalfund.org/media/dp3clsrr/cr_c19rm-psa-vpsa-vsa_technical-briefing-note_en.pdf)
- [WHO, Foundations of medical oxygen systems (17 February 2023), sections 2.1 and 2.2](https://iris.who.int/server/api/core/bitstreams/4ad6f5fd-089e-4142-8439-b64e98d816d8/content)
- [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)
- [The International Pharmacopoeia, 13th edition (2025), Medicinal oxygen](https://digicollections.net/phint/202502/index.html#d/b.6.1.226)
- [ULTRAOX SC datasheet, p. 2 and p. 5](https://www.ultracontrolo.com/products/ultraox)
- [ULTRAOX ST datasheet, p. 2 and p. 5](https://www.ultracontrolo.com/products/ultraox-st)
- [ULTRACON datasheet, p. 2](https://www.ultracontrolo.com/products/ultracon)
- [ULTRAOX VSA datasheet, p. 2 and p. 3](https://www.ultracontrolo.com/products/ultraox-vsa)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/compare/psa-vs-vsa-vs-vpsa/