# Should a PSA plant have redundant dryers and condensate drains?

**Should the air treatment of a PSA oxygen plant have duplicate dryers, filters or condensate drains to protect the zeolite?**

NHS England's HTM 02-01 (2026) asks for a PSA plant's filters and molecular sieves to be duplexed, each able to work independently, and says its desiccant dryers are usually integrated within the sieves; the 2020 WHO interim specification (superseded in 2024) asked for a dryer and pre-filters with automatic drains.

## What HTM 02-01 duplicates in a PSA plant

- Compressors: a duplex compressor; where more than two are installed, the system should deliver the design flow with one compressor out of service (paragraph 6.116).
- Air treatment and sieves: duplexed filters and duplexed molecular sieves, one adsorbing while the other regenerates. All duplexed components should be capable of independent operation, and the general resilience principles of a medical air plant should be followed.
- Dryers: desiccant air dryers are usually integrated within the molecular sieves and do not regenerate independently; refrigerant dryers may be added where the environment requires them (6.120).
- Compressor standard: compressors for PSA systems should comply with the medical air requirements of Chapter 7, and the medical air plant itself should not be used for the PSA plant (6.117).

## What HTM 02-01 asks of a medical air plant

Chapter 7, on medical air plants, duplicates the whole dryer assembly with a second assembly to ensure continuity of supply, each with its own dew-point sensor and test point. It asks for electrically operated automatic drains on receivers, as these have been found more reliable, with a manual drain as a bypass in case of power loss, and for automatic drainage traps on the after-coolers, receivers, separators and coalescing filters, their discharge piped to an oil separator. It also asks for oil filters and water separators to be individual components, for resilience and efficiency. These paragraphs are written for medical air plants; for the PSA plant, HTM refers to medical air requirements for the compressors and to the general resilience principles above.

## Drains in daily operation

- The USAID RISE operating procedure (2022), written for hospitals in India, says never to run the plant if the automatic water drains are faulty or not draining properly, to check residual water by opening the manual drain valve, and to test the automatic drain valve every month. It also asks for at least two compressors with each PSA plant.
- The Global Fund daily maintenance checklist asks whether the compressor condensate is draining correctly.
- PATH (November 2023) lists clogged filters and drains, causing reduced flow or overheating, among the common issues of PSA plants in disrepair.

## Why the sieve needs dry air

AIGA 113/20, adopted from EIGA Doc 195, asks for a drying and filtration system downstream of the compressors to deliver dry and oil-free air at the inlet of the adsorber vessels, notes that an increase in moisture would lead to accelerated damage of the adsorbers, and asks the healthcare facility's quality management system to ensure that the supply system is available at all times, even under single fault condition. The USAID procedure says dried air eliminates operational issues in the molecular sieves and solenoid valve. The 2020 WHO interim specification also asked for an external air dryer sized to the compressor output and an alarm when the dryer pressure dew point rises above 3 °C.

## ULTRAOX plants

The ULTRAOX SC and ST basic configurations list one, two or more compressed air treatment chains. The ULTRAOX 2022 datasheet lists a water separator with electronic drain in the air treatment package and an ULTRASEC refrigeration dryer with automatic condensate evacuation, a digital dew point indicator and a dry contact alarm; the customer provides the condensate drainage at the site. See [what air treatment a PSA plant needs](https://library.ultracontrolo.com/answers/what-air-treatment-does-a-psa-plant-need/).

### What if an automatic condensate drain fails?

The USAID procedure says not to run the PSA plant with malfunctioning drains and to check for residual water with the manual drain valve; HTM 02-01 gives medical air receivers a manual drain as a bypass in case of power loss.

### Can a PSA plant share the hospital's medical air plant?

HTM 02-01 (2026) says the medical air plant should not be used for the PSA plant, and AIGA 113/20 asks for the oxygen 93 air compressor to be dedicated and not shared with the medical air supply.

## Sources

- [NHS England, HTM 02-01 Part A (2026), paragraphs 6.116, 6.117, 6.120, 7.50, 7.56, 7.57, 7.64, 7.67 and 7.68](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)
- [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)
- [USAID RISE, Standard Operating Procedures: PSA Plant Operations and Preventive Maintenance by the Facility Management (2022)](https://media.path.org/documents/SOP_on_PSA_Plant_USAID_RISE_04032022_F7fUBr6.pdf)
- [Global Fund / Build Health International, PSA plant Daily Maintenance Checklist (2025)](https://resources.theglobalfund.org/media/xbanfgrc/cr_c19rm-psa-plant-daily-maintenance_checklist_en.pdf)
- [PATH, Pressure swing adsorption plants: Common issues and solutions to prevent future disrepair (November 2023)](https://media.path.org/documents/Root_cause_analysis_report_external_clean_v2.pdf)
- [AIGA 113/20 (adopted from EIGA Doc 195), On site generation of oxygen 93% for medicinal use, sections 4.3.1, 6.12, 7.2.1 and Table 5](https://asiaiga.org/uploaded_docs/en_AIGA_113_20_Generation_of_Oxygen_93_for_Medicinal_Use.pdf)
- [ULTRAOX SC datasheet, p. 2; ULTRAOX datasheet 2022, p. 9, p. 12 and p. 16](https://www.ultracontrolo.com/products/ultraox)
- [ULTRAOX ST datasheet, p. 2](https://www.ultracontrolo.com/products/ultraox-st)
- [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/should-a-psa-plant-have-redundant-dryers-and-drains/