Legionella Management Specialists

Expansion / Pressurised Vessels

 

Pressurised water systems may be fitted with pressurisation vessels, These can range in volume from approximately 4 Litres to 60 Litres. These generally contain a gas such as nitrogen which the water compresses across a suitable membrane (bladder) during the pressurisation phase. When these units are incorporated into systems a dead leg is created. The installation of these vessels must be as close as possible to the system pipework to minimise the dead leg created. A suitable drain must be fitted to enable flushing of the dead leg on a quarterly basis if 15 litres or above/ Bi-Annual basis if below 15 litres or as indicated by risk assessment. Pressurisation vessels must be maintained in accordance with manufacturers’ guidelines with the bladder being changed at the recommended intervals. It is also possible to fit an Anti-Legionella Expansion Vessel or retro fit the current expansion vessel with an Anti-Legionella Valve as per the HSG 274 Part 2 Para 2.39-2.39.

 

To minimise the risk of microbial growth, expansion vessels should be installed or adapted using the below guidance.

 

■ in cool areas on cold flowing pipes;

■ mounted as close to the incoming water supply as possible;

■ mounted vertically on pipework to minimise any trapping of debris;

■ with an isolation and drain valve to aid flushing and sampling;

■ to minimise the volume retained within them;

■ designed to stimulate flow within the vessel’s