# Why does a medical air plant run all the time?

**Why does a hospital medical air plant run continuously, and how are leaks found?**

Under HTM 02-01 (2026), the NHS England guidance, air for respiratory use such as patient ventilation can be used continuously, and medical air compressors should be suitable for continuous running on load and high-frequency start/stop, or VSD-controlled; Part B lists pipeline leak tests and asks for quarterly tests of every outlet, including for leaks.

## Demand that does not stop

HTM 02-01 Part A contrasts surgical air with air for respiratory purposes. Surgical air is used at high flow rates and pressures, up to 350 L/min, but for relatively short durations. Air for respiratory purposes is used at much lower flow rates, typically less than 80 L/min for patient ventilation, but its use can be continuous, and medical air demand typically involves several terminal units in use at the same time. Pneumatically powered ventilators can use up to 80 L/min of free air continuously.

The compressors may be of any type, provided they are suitable for continuous running on load and for high-frequency start/stop operation, or controlled by variable speed drives (VSDs). All plant designs should consider VSD compressors, and a combined medical and surgical air plant with VSDs can modulate flow to suit demand. When an MGPS is designed, the intention should always be to use the most efficient pumps and compressors and to remove unused and unnecessary gases and terminal units.

## What the plant records show

- Hours and current: compressor plant control systems should include an hours-run counter, and each compressor's control system a means of accurate current measurement. The weekly tasks include recording the hours run for each compressor, the running current of the duty compressor and the compressor cut-in and cut-out levels, and making sure both compressors are left in auto mode.
- Maintenance: Part B says the counter readings can be used with the manufacturers' recommendations to modify the maintenance programme.
- Consumption at low demand: the plant's testing procedure should evaluate its efficiency by testing power consumption at 100%, 10% and 0% of the system design flow, and consumption at zero flow should be less than 1% of that at 100% design flow.

## Leaks and equipment left connected

A fact sheet on leaks from the Compressed Air Challenge (May 2026), written for industrial compressed air systems, says leaks sometimes waste 20 to 30% of a compressor's output and force equipment to cycle more frequently, and that increased running time can lead to additional maintenance and unscheduled downtime; leakage should be less than 10% in a well-maintained system. It recommends an ultrasonic acoustic detector to detect leaks, with soapy water as a simpler method that is reliable but time consuming, and says equipment no longer in use should be isolated with a valve.

For a hospital pipeline, HTM 02-01 Part B lists these leak checks (more methods are on [how to detect leaks in a medical gas network](https://library.ultracontrolo.com/answers/how-to-detect-leaks-in-a-medical-gas-network/)):

- Terminal units: all should be tested quarterly, inserting a blank probe to test gas-specificity, mechanical function and leaks.
- Pipeline leak tests: PPLx is a leak test of 2 to 24 hours on the system at working pressure using digital gauges; PPLF uses leak detector fluid and is generally used for small modifications of fewer than 20 joints where all joints are accessible.
- Exposed pipework: external runs, and internal runs in risers or corridors, should be inspected at least annually, including for leaks from fittings.

## Ultra Controlo medical air plants

In the [ULTRAAR SCA](https://library.ultracontrolo.com/products/ultraar-sca/), each compressor has its own pressure switch for automatic starting and stopping at the preset pressure, and in automatic mode the compressors alternate to guarantee uniform wear; the datasheet says these modes are there to guarantee the continuous supply of the network at the preset regulation pressure; the control panel has an hour meter and a running signal for each compressor. The ULTRAAR SC uses ULTRACECO SC scroll compressors, whose QuAir PLC controller starts and stops the skids automatically, with the aim of saving energy and lifetime of the scroll unit.

### Can a medical air compressor be designed to run continuously?

Yes. HTM 02-01 (2026) accepts any compressor type that is suitable for continuous running on load and for high-frequency start/stop operation, or that is controlled by variable speed drives.

### How are leaks at medical air outlets found?

HTM 02-01 Part B asks for every terminal unit to be tested quarterly with a blank probe for gas-specificity, mechanical function and leaks.

## Sources

- [NHS England, HTM 02-01 Medical gas pipeline systems, Part A (2026), paras 1.8, 4.83, 7.2, 7.6 to 7.8, 7.32, 7.43 and 7.85](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)
- [NHS England, HTM 02-01 Medical gas pipeline systems, Part B (2026), paras 11.113 and 11.213, weekly tasks for medical gas plant, pipework inspection tasks and Table 2](https://www.england.nhs.uk/wp-content/uploads/2016/05/health-technical-memorandum-02-01-medical-gas-pipeline-systems-part-b-operational-management-aug-26.pdf)
- [Compressed Air Challenge, Compressed Air Systems Fact Sheet #7: Compressed Air System Leaks (May 2026, Rev. 1)](https://www.compressedairchallenge.org/data/sites/1/media/library/factsheets2026/fact-sheet-7-compressed-air-system-leaks_updated2026.pdf)
- [ULTRAAR SCA datasheet, p. 3](https://www.ultracontrolo.com/products/ultraar-sca)
- [ULTRAAR SC datasheet, p. 3](https://www.ultracontrolo.com/products/ultraar-sc)
- [ULTRACECO SC datasheet, p. 2](https://www.ultracontrolo.com/products/ultraceco-sc)

Reviewed: 2026-10-23. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/why-does-a-medical-air-plant-run-all-the-time/