Pipeline systems
Outlet check valve (terminal unit check valve)
An outlet check valve, as HTM 02-01 (2026), the NHS England guidance, describes it, is the integral isolating valve or check valve of a terminal unit that operates automatically when the socket assembly is removed; with it, work on that terminal unit does not usually require interrupting the supply to adjacent units.
Part B also refers to an automatic isolating valve, or check plate, within the first-fix assembly, as in BS 5682 and BS EN ISO 9170-1 terminal units; with these, a live repair of a terminal unit needs no physical break in the pipeline. Part B adds that some earlier terminal units include a manual isolating valve, and that termination blocks should not be left unattended with the socket removed unless a blocking plate has been attached. ISO 9170-1:2017 is intended to ensure the gas-specific assembly, mechanical resistance, flow, leakage and pressure drop of terminal units.
The 2012 practice guide on fluides médicaux coordinated by OMEDIT PACA-Corse lists double-valve outlets (prises à double clapet) among the characteristics of wall outlets, allowing work on the outlet without cutting off the whole supply. HTM 02-01 also mentions check valves elsewhere: NIST connectors incorporate a check valve for all pressure gases, and AGS terminal units should be checked to confirm that their check valve operates satisfactorily.
Sources
- NHS England, HTM 02-01 (2026) Part B, paragraphs 7.21 and 7.78
- NHS England, HTM 02-01 (2026) Part A, paragraphs 15.124 and 19.171
- ISO 9170-1:2017, Terminal units for medical gas pipeline systems, Part 1 (iso.org abstract)
- OMEDIT PACA-Corse, Guide interrégional de pratiques pharmaceutiques en matière de fluides médicaux en établissement de santé (December 2012), wall outlets
Ultra Controlo figures come from its technical datasheets. Third-party facts were read at the source on the date shown.