Isolating Valve
/ ˈaɪsəleɪtɪŋ valv /
Also known as: service valve, ball valve, gate valve, quarter-turn valve, inline isolator
Definition
An isolating valve is a shut-off valve fitted in a pipework run to allow a section of the system or a single appliance to be isolated from the water supply without shutting off the whole property. Required by the Water Supply (Water Fittings) Regulations 1999 before every water fitting and appliance. Main types: ball valve (quarter-turn lever, reliable and clear open/closed indication, preferred for new work); gate valve (multi-turn, common in older systems, prone to seizing); service valve (flat-head screw, used under cisterns and behind appliances). A lockshield valve on a radiator return is a type of isolating valve set by the engineer during commissioning.
In practice
The most common practical problem with isolating valves in older properties is that they have not been operated for years and have seized solid - when a plumber tries to close the valve to isolate a tap for replacement, it will not turn. Gate valves are particularly prone to this failure; ball valves are more reliable but can also stick if not operated for many years. Exercising (turning fully open to closed and back) all isolating valves annually prevents seizing. When a valve cannot be turned, the next valve upstream must be used to isolate the section - which may mean turning off the water to a larger section of the property.
Gate valves found in older heating systems should be replaced with ball valves at the next opportunity. The multi-turn operation of a gate valve means it is slow to close in an emergency, and the partly-open position creates turbulence and erosion in the valve body. For heating circuits (radiator connections, boiler connections, pump connections), angled radiator valves and service valves specifically rated for heating use (able to withstand the higher water temperatures and corrosion inhibitors used in heating systems) should be used rather than standard cold water service valves.