How compression and push-fit joints work, and where each is a sensible choice.
Not every joint is soldered. Two very common mechanical joints, compression and push-fit, let you connect pipe without a flame, and Level 2 expects you to know how each works and when to reach for it.
A compression joint uses a body, a soft metal ring called an olive, and a cap nut. As the nut is tightened, it squeezes the olive onto the pipe and into the body, and that deformed ring makes the watertight seal. It does not need heat, which suits work near flammable materials or where a flame is awkward.
A push-fit joint seals a different way. Inside the fitting an O-ring makes the seal against the pipe, and a toothed grab ring grips the pipe to hold it in place once it is pushed home. Many are designed to be released with a special tool or collar so they can be taken apart again.
The trade-offs guide the choice. Compression joints are demountable, reliable on accessible pipework and need only spanners, but they take longer and rely on correct tightening. Push-fit is quick, needs no tools and no flame, and copes well with damp or awkward spots, though the fitting is bulkier and the pipe must be fully inserted.
Both share a non-negotiable: the pipe end must be cut square, deburred and left clean and round, because a burr or an out-of-round end can cut the O-ring or stop the olive sealing. A pipe insert is used to keep plastic pipe round inside the fitting.
For revision, picture the seal: a squeezed olive under a nut is compression; an O-ring and grab ring you push onto is push-fit. Both avoid heat, both need a clean square pipe end, and the right choice depends on access, speed, and whether you need to take the joint apart later. Follow the fitting maker instructions for the pipe and fitting in use.
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