Making compression and push-fit joints

Learn to join copper or plastic pipe using compression and push-fit fittings, and test that the joint is watertight.

CJ-01Know the two joint types before you startA compression joint uses a nut and a small brass ring called an olive, squeezed onto the pipe with two spanners, to make a seal. A push-fit joint (sometimes called speed-fit) has an internal rubber ring and a grab-ring, and you simply push the pipe in by hand - no tools needed. Both work on copper or plastic pipe. Push-fit is faster and needs no tools, but compression is often preferred where a joint will be hidden and needs to be as reliable as possible.

CJ-02Cut the pipe dead square and deburr itUse a pipe cutter (a tool that clamps around the pipe - you tighten it a little and rotate it round the pipe repeatedly until it cuts through) or a hacksaw with a mitre block to keep the cut straight. A cut that's even slightly angled will never seal properly in either joint type. Afterwards, remove the sharp burr from inside and outside the cut edge with a file or the small blade built into most pipe cutters - a burr stops the olive gripping and can snag a push-fit O-ring.

CJ-03Isolate the water before you cut into any existing pipeIf you're cutting into a pipe that's already connected to the water system, turn the water off at the stopcock (the main shut-off valve, often under the kitchen sink or where the supply enters the house) first. Open a nearby tap to drain the pipe and let any remaining water run into a container or towel. Treat every pipe as full until you've proven otherwise by draining it - don't assume it's empty just because the tap upstream is off.

CJ-04Make a compression jointSlide the nut onto the pipe first, then the olive, then push the pipe fully into the fitting body until it stops against the internal shoulder. Slide the olive up against the fitting, then tighten the nut by hand, then use two spanners - one to hold the fitting body still, one to turn the nut - about one full turn past hand-tight. It should go firm and then stop; if you're still cranking hard, stop, because that splits the olive or distorts the pipe rather than sealing it.

1 each · Compression fitting (15mm)

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1 roll · PTFE tape

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CJ-05Make a push-fit jointMeasure the depth of the fitting's socket and mark that distance on the pipe with a pen - this tells you how far the pipe needs to go in. Push the pipe in firmly and evenly until you feel it hit the internal stop; the mark should just disappear into the fitting. If you're joining plastic barrier pipe, push a pipe insert (a small stiffening sleeve) into the pipe end first - without it, the pipe can collapse slightly when gripped and the joint will leak. This step is the one beginners forget most often.

1 each · Push-fit fitting (15mm)

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1 each · Pipe insert (for plastic pipe)

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CJ-06Check you've actually got it rightTurn the water back on slowly at the stopcock and watch the joint for at least a minute. Run a dry finger along it rather than just looking - a slow leak often feels damp before you can see it. On a push-fit joint, gently try to pull the pipe out; it shouldn't move at all. Leave the joint and check again after ten minutes, since a slow weep can take a little while to show.

CJ-07Know how to fix it if it leaksA weeping compression nut can sometimes be cured by a small extra turn, but if it keeps weeping, take it apart and check the olive and pipe end for damage or dirt rather than just tightening harder. Once an olive has been compressed onto a pipe it's deformed to that shape, so always fit a new olive if you remake the joint - never reuse one. A leaking push-fit joint usually means the pipe wasn't pushed in fully or the cut end wasn't square - pull it out, recut and deburr, then try again.

1 each · Replacement olive

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