# What is the cycle time of a PSA oxygen generator?

**What is the cycle time of a PSA oxygen generator, and what controls it?**

NHS England's HTM 02-01 (2026) and a Global Fund note (2025) describe the PSA cycle as two sieve beds alternating, one adsorbing while the other regenerates. Neither gives a cycle time in seconds: HTM asks for the operating system to control the sieves, and a USAID RISE procedure for Indian hospitals cites the manufacturer's manual.

## How the cycle works

The Global Fund and Build Health International briefing note on PSA, VPSA and VSA (4 March 2025) explains that nitrogen sticks to the zeolite in a sieve bed when compressed air passes through it. Once the zeolite is saturated with nitrogen, the nitrogen is removed by lowering the pressure, and the zeolite is ready to repeat the process in a continuous cycle. In a PSA plant, two sieve bed tanks alternate between producing oxygen and releasing nitrogen to the outside air, to give a near continuous production of oxygen.

HTM 02-01 (2026), the NHS England guidance, describes the same arrangement in Part A, paragraph 6.110: the sieve units are arranged in pairs, one adsorbing while the other regenerates, and the waste product, essentially nitrogen, is discharged to atmosphere during regeneration. Regeneration uses a proportion of the product gas, and the HTM asks for this consumption to be taken into account when sizing the plant. Paragraph 6.119 asks for duplex molecular sieves in pairs to enable continuous oxygen generation.

The ULTRACON datasheet describes a unit with two columns, each going through a cyclic sequence of high and low pressure steps: in the high pressure step the adsorbent retains the contaminants in the compressed air and oxygen is obtained, and regeneration takes place in the low pressure step, with the release of the retained contaminants. A USAID RISE procedure written for PSA plants in hospitals in India (PDF of March 2022) adds that, during the desorption phase, solenoid valves let the nitrogen from the two towers be exhausted.

## Is there a standard cycle time?

None of the documents cited on this page gives a cycle duration. HTM 02-01 lists control of the molecular sieves among the functions the plant's operating and indicating system should perform (6.123) and asks for the molecular sieve control unit to be an independent unit (6.131). The USAID procedure says the time cycle of the PSA unit starts once the air receiver reaches the pressure given in the original equipment manufacturer's manual, asks the operator to check that all valves operate as per the PLC program, and refers any abnormality to the troubleshooting steps in the manufacturer's manual. The Global Fund's standard operating procedure template for oxygen plant operators (9 December 2025) states that its procedures and parameters may not suit every plant model and do not replace the manufacturer's instructions.

## What operators check

- Valve sequence: at start-up, that the valves follow the PLC program (USAID procedure).
- Equalisation valve: among the checks for low purity, that the equalisation valve is closed during oxygen production and the regeneration of the other bed (USAID procedure).
- Yearly: that the drying and regeneration cycles are functioning (USAID procedure, annual inspection).
- Shutdown: run the plant for a few cycles until the pressure gauges on the generator towers read zero (USAID procedure).
- Restart after a long stop: in its section on plants that run less than once a week, the Global Fund template says the plant must run several complete cycles before purity returns to 93% ± 3%, which can take from a few minutes to several hours, and that a purge valve may need to be opened by hand to vent the low-purity product.

## On ULTRAOX plants

ULTRAOX plants use ULTRACON concentrators with two molecular sieve columns and a zeolite adsorbent, and have a digital touch screen and a PLC (ULTRAOX datasheet 2022, p. 14 and p. 16). The plant starts and stops oxygen production automatically in response to demand from the downstream distribution system (p. 6), and the ULTRAOX SC datasheet states that the equipment is parameterised and tested in the factory and will be ready to start on site.

### Do the standards give a PSA cycle time?

None of the documents cited on this page gives one. HTM 02-01 (2026) lists control of the molecular sieves among the functions the plant's operating and indicating system should perform, and the USAID RISE procedure, written for hospitals in India, refers operators to the manufacturer's manual.

### How many cycles does a PSA plant need to reach purity after a stop?

The Global Fund operator SOP template (2025) says several complete cycles after a period of inactivity, from a few minutes to several hours. See [how fast a PSA plant reaches purity](https://library.ultracontrolo.com/answers/how-fast-does-a-psa-plant-reach-purity/).

## Sources

- [ULTRACON datasheet, p. 2](https://www.ultracontrolo.com/products/ultracon)
- [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)
- [NHS England, HTM 02-01 (2026) Part A, paragraphs 6.110, 6.119, 6.123 and 6.131](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, Modèle de procédure opérationnelle standard pour les opérateurs de centrales de production d'oxygène (9 December 2025), template notes and section 9.3](https://resources.theglobalfund.org/media/atepwfny/cr_c19rm-sop-oxygen-plant_template_fr.docx)
- [ULTRAOX datasheet 2022, p. 6, p. 14 and p. 16](https://www.ultracontrolo.com/ultraox)
- [ULTRAOX SC datasheet, p. 3](https://www.ultracontrolo.com/products/ultraox)

Reviewed: 2026-10-23. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/what-is-the-cycle-time-of-a-psa-oxygen-generator/