Fit a service valve under your sink so you can shut off water to a tap or appliance without turning off the whole house.
ISV-01Turn off the water and drain the pipeFind your stopcock, usually under the kitchen sink, and turn it clockwise until it stops. Open the tap the pipe feeds to let any pressure and remaining water drain out. Put a bowl and old towel under the pipe you're working on, because some water will always be left in the line.
ISV-02Clear the cupboard and support the pipeEmpty the cupboard under the sink so you've got room to work and can see the full pipe run. If the pipe isn't already clipped, hold or support it so it doesn't flex or drop when you cut it. Lay down a bit of dust sheet or cardboard to protect the cupboard base.
ISV-03Mark and cut the pipeMark the pipe where the valve will sit, leaving enough clearance either side to fit the valve body and turn it once fitted. Cut the pipe square using a pipe cutter — a rocked hacksaw cut will leave the joint leaking. Deburr the cut end inside and out with a file or the deburring blade on the cutter.
ISV-04Check the valve orientation and dry-fit itIsolating valves have an arrow on the body showing the direction of flow — this must point away from the stopcock, towards the tap or appliance. Slide the valve onto the cut pipe ends without any jointing compound or tape yet, just to check the fit and alignment. If it's a push-fit valve, check the pipe goes in fully to the marked insertion depth, usually 20-25mm.
ISV-05Make the jointsFor a compression valve, slide the nut and olive onto the pipe, push the pipe fully into the valve body, then tighten the nut by hand and finish with a spanner — usually one full turn past hand-tight, no more. For a push-fit valve, just push the pipe firmly past the internal grab ring until it stops. Wipe off any excess jointing compound and leave the joint undisturbed while it settles.
ISV-06Reconnect to the tap or applianceConnect the outlet side of the valve to the tap tail or appliance using a flexible tap connector, unless the pipe run continues in solid copper or plastic. Hand-tighten the connector nut, then finish with a spanner, holding the valve steady so it doesn't twist and strain the first joint.
ISV-07Turn the water back on and check for leaksOpen the stopcock slowly, not all at once, so the pipework fills gently rather than getting a pressure knock. Check every joint you've made, plus the valve body itself, for drips or damp patches. Run the tap for a minute to clear any grit, and check the joints again once water has been flowing.
ISV-08Test the valve and tidy upTurn the isolating valve off and on a few times to check it moves smoothly and shuts off the water fully. Dry the pipework and cupboard base, and check again after a few hours for any slow leaks that only show up once the joint has been under pressure a while. Put your stored items back and dispose of any old fittings.
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