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Short answer: an oxygen plant is an on-site system that makes oxygen from ambient air at the point of use. At hospital level, the Global Fund and Build Health International briefing note identifies three common designs, PSA, VPSA and VSA, which all produce oxygen of approximately 93% purity by separating it from nitrogen with zeolite. They differ in pressure, number of sieve beds and whether an extra compressor is needed before the oxygen can enter a piping network.
This is general product information for laboratory, clinic and supply staff. It is not medical advice and not a design or commissioning procedure.
Definition and scope
In the briefing note’s wording, PSA (pressure swing adsorption), VPSA (vacuum pressure swing adsorption) and VSA (vacuum swing adsorption) are the three systems “commonly used to produce oxygen at a hospital level”. Each one takes atmospheric air, passes it through a tank of zeolite called a sieve bed, and delivers a high-purity oxygen stream of approximately 93%.
Oxygen plant, oxygen generator and PSA oxygen plant
These phrases overlap. A “PSA oxygen plant” is the PSA variant of the plant described here. “Oxygen generator” is also used for the sieve-bed unit inside a plant, so check which equipment a document means. A single-patient device is a different product: see what an oxygen concentrator is.
How a PSA-type plant makes oxygen
According to the briefing note, compressed air is passed through zeolite in a sieve bed. Under pressure, nitrogen sticks to the zeolite and an oxygen-rich stream leaves the bed. When the zeolite is saturated, lowering the pressure releases the nitrogen, and the cycle repeats continuously.
In a PSA plant specifically, the note describes this chain:
- Two sieve bed tanks that alternate, so one is producing while the other is releasing nitrogen.
- An air compressor that pressurizes incoming air to 4.5-7 bar.
- An air dryer, needed because moisture condenses at high pressure.
- An air storage tank ahead of the generator.
- Oxygen leaving at pipeline-capable pressure, 3.5-5 bar, for wall-mounted outlets. It can also feed a high-pressure booster used to fill cylinders.
PSA vs VPSA vs VSA
All figures below are from the same briefing note (Global Fund / Build Health International, published 4 March 2025).
| Feature | PSA | VPSA | VSA |
|---|---|---|---|
| Sieve beds | 2 | 2 | 1 |
| Air entering the beds | 5-7 bar | about 0.5 bar | about 0.7 bar |
| Air handling | Air compressor plus dryer | Lobe compressor plus vacuum pump | One lobe compressor (reversible blower) for air and exhaust |
| Extra compression to pipe oxygen at 4-6 bar | None | Scroll compressor | Scroll compressor |
| Main trade-off named by the note | Large plants have high compressor in-rush currents; more filters to replace | Lower average power; extra oil-free booster; reports of low purity | Lower average power, but savings may not be realized in smaller plants; specialized maintenance tools |
The note adds that if national standards require piping above 6 bar, a medium-pressure booster can raise 4-6 bar oxygen to 11-12 bar.
What to check before a plant is specified or commissioned
The briefing note’s own comparison points translate into a short checklist for the people who write requirements or review offers. Each item comes from the note.
- Pipeline pressure. PSA oxygen exits at about 4 bar with no extra booster. VPSA oxygen reaches a buffer tank at about 0.5 bar and VSA oxygen at about 0.7 bar, too low for direct piping, so a scroll compressor is added.
- Electrical sizing. Large PSA plants have high compressor in-rush currents, so the generator and switchgear must be sized for it. For VSA the note says peak operating power is the same as PSA, so the generator and switchgear size is the same.
- Consumables. PSA uses more filters, including for oil from a rotary screw compressor, and these need replacement.
- Extra equipment and failure points. VPSA and VSA both need an additional oil-free oxygen booster compressor, and the note says additional compressors add potential failure points.
- Cylinder filling. A PSA plant can feed a high-pressure booster to fill cylinders.
- Local support. The note recommends choosing the technology already common and functional in the region, and standardizing tools, skills and spare parts. It credits PSA with a wider knowledge base and more established supply chains and service networks, and warns that for VPSA and VSA, spare parts supply and maintenance support may not be optimal in countries where such plants are not common.
Where piped oxygen reaches wards, the distribution side is governed separately; see the NFPA 99 health care facilities code guide. For outlets and regulators at the point of use, see oxygen regulators and headwall units.
Common misunderstandings
- “All on-site plants deliver oxygen at the same pressure.” They do not. Output ranges from about 0.5 bar (VPSA) and 0.7 bar (VSA) to pipeline pressure (PSA) before any added compression.
- “The vacuum designs are always cheaper to run.” The note says VSA power savings may not be realized for smaller plants, and its peak power matches PSA.
- “Plant oxygen is pure oxygen.” The note describes approximately 93% oxygen, produced by removing nitrogen from air.
FAQ
What is an oxygen plant?
An on-site system that separates oxygen from nitrogen in atmospheric air using zeolite sieve beds. At hospital level the common types are PSA, VPSA and VSA, producing approximately 93% oxygen.
What is a PSA oxygen plant?
A plant that uses two alternating sieve beds fed with air compressed to 4.5-7 bar, with an air dryer and air storage tank, delivering oxygen at pipeline-capable pressure of 3.5-5 bar.
Is an oxygen generator the same as an oxygen plant?
Not necessarily. “Generator” is used for the sieve-bed unit inside a plant, so confirm what a given document describes.
How do PSA, VPSA and VSA differ?
They use the same zeolite air-separation process but differ in pressure levels and equipment: PSA and VPSA use two sieve beds and VSA uses one, and only PSA delivers oxygen at pipeline pressure without extra oxygen compression.
Sources
- Global Fund and Build Health International (Project BOXER), Briefing Note: Pressure Swing Adsorption, Vacuum Pressure Swing Adsorption, and Vacuum Swing Adsorption, 4 March 2025. Available at resources.theglobalfund.org (briefing note PDF). Checked 30 October 2026.
- World Health Organization, WHO-UNICEF technical specifications and guidance for oxygen therapy devices, 14 January 2019, covering selection, procurement, use and maintenance of oxygen therapy products. Checked 30 October 2026.
