# Why does bedside suction lose power?

**Why does suction at a hospital bedside outlet become weak, and what should be checked?**

Bedside suction becomes weak when something between the patient and the vacuum plant restricts flow: a full drainage jar or wet hydrophobic filter that shuts the line by design, a faulty terminal unit, pipework partly blocked by aspirated fluids, or plant bacteria filters that are wet or past their pressure drop limit.

HTM 02-01 (2026) sets the design reference in England: the pipeline should hold at least 315.5 mmHg of vacuum at the front of the most distal terminal unit with 40 L/min flowing. The checks below start at the bedside and move towards the plant.

## At the bedside

- Drainage jar: jars are fitted with floats, often used with an anti-foaming agent, to stop fluid carrying over into the pipeline. When the float closes, suction through that jar stops.
- Hydrophobic filter: the tubing between the jar and the suction controller is often protected by a hydrophobic filter, which effectively seals the tube once the filter becomes wet.
- Suction controller: controllers have integral filters and floats that keep aspirated fluid out of the pipework.
- Terminal unit: HTM 02-01 Part B lists a quarterly test of terminal units for gas-specificity, mechanical function, leaks, flow and pressure drop, with the actual frequency set by the healthcare organisation.

## In the pipeline and at the plant

- Area alarm: area alarm panels show a vacuum fault and display the vacuum reading on the fascia.
- Fluid in the pipework: repeated aspiration of fluids can block the pipeline as transported and dissolved solids dry out. Any contamination incident should be reported at once to the Authorised Person (MGPS) and the infection prevention and control team.
- Bacteria filters: filters should be changed at the manufacturer's intervals, and more often if a filter becomes wet or its pressure drop exceeds the supplier's specification. A drain flask with liquid in it should not be opened without consulting the Authorised Person (MGPS) and the infection prevention and control team.
- Pumps: the plant should be able to reach a higher vacuum than the pipeline needs, to overcome bacteria filter resistance and exhaust back pressure.

ULTRAVAC plants have two bacterial filters with liquid separator. The filters have vacuum differential gauges and isolating valves, and a transparent liquid separator or drain flask collects liquids and impurities to protect the filter element.

### How often should vacuum outlets be tested?

HTM 02-01 Part B (2026) lists terminal unit maintenance as a quarterly task, with the actual frequency set by the healthcare organisation according to the use, age and design of the units.

### What should staff do if fluid has been sucked into the vacuum pipeline?

Report it at once to the Authorised Person (MGPS) and inform the infection prevention and control team, as HTM 02-01 Part B asks for any contamination incident.

## Sources

- [HTM 02-01 (2026) Part A, 10.3, 10.26, 10.34, 14.43 and Table 23](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)
- [HTM 02-01 (2026) Part B, 11.123, 11.132, 11.181, 11.213 to 11.218](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)
- [ULTRAVAC datasheet, p. 2 and 3](https://www.ultracontrolo.com/products/ultravac)

Reviewed: 2026-10-22. Ultra Controlo engineering. https://library.ultracontrolo.com/answers/why-does-bedside-suction-lose-power/