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.
Copper compression fittings come in two types. Type A, non-manipulative, is the everyday fitting for half-hard tube above ground: the olive bites into the plain tube as the nut is tightened. Type B, manipulative, is for soft coiled tube and for work underground: the tube end is opened out with a flaring tool, so the fitting grips the tube inside and out and supports its soft wall.
A typical pressure push-fit fitting seals against the pipe with an O-ring and holds it with a retaining ring. Many can be released with their specified tool or collar. This is different from a waste ring-seal socket; use the components and pipe specified for the system.
Compression joints need suitable spanners, access for correct tightening and support against unwanted movement. Pressure push-fit fittings can be assembled quickly without jointing heat, but still need tools for cutting and preparation, the correct insert where specified and a check of full insertion. A damp or awkward spot does not change those needs, and not every fitting suits it.
Both need a clean, round pipe end prepared by the method specified for that material and fitting. Remove harmful burrs without damaging the sealing surface. Use the matching support insert where the plastic pressure system requires one; an insert does not correct a skew cut or a damaged pipe.
Wavin's Hep2O shows how one plastic push-fit system puts this into practice. Cut the pipe squarely with the recommended cutters, never a hacksaw, at one of the '^' marks printed along it: the distance between two marks is the insertion depth into a fitting, so cutting at a mark allows for it. Fit the support sleeve into the cut end before making the joint. Where hidden pipe is held with cable ties instead of clips, leave the ties loose enough for the pipe to slide, because it moves as it warms and cools.
Picture the two functions separately: the compressed olive seals the compression connection; the O-ring seals and the retaining ring grips in a pressure push-fit connection. Choose by service suitability, access and maintenance needs, then follow the fitting maker’s preparation, assembly and testing instructions.
Serviceable connections
Where a connection may need to come apart again for servicing, such as a tap tail to its supply pipe, a tap connector with a union nut and a fibre or rubber washer is a sensible choice. It can be undone without disturbing the rest of the pipework, unlike a soldered or solvent-weld joint, which is permanent, or a plain threaded joint made up with no union, which may need the pipe run itself to be turned to release it.