How to fit an isolation valve into pipework using a quarter-turn compression isolation valve.
Isolation valves are normally easy to fit as the majority of them are compression or push fit, you can get valves that require soldering, but they are not as common and can be tricky to install without damaging the isolator.

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Isolation valves are useful, because you can service items without having to isolate the water to the whole property. Ideally when installing a compression isolation valve, if you tighten the nut finger tight, then give the nut ¾ of a turn using a spanner/wrench that should be sufficient.