A compression fitting is a demountable pipe joint made up of three parts: the fitting body, a nut and a compression ring, usually called an olive. Tightening the nut deforms the brass or copper olive and wedges it between pipe and body. That deformed ring makes the joint watertight and gastight without soldering, pressing or gluing.
Compression fittings are made for copper tube in the common sizes 12, 15, 22 and 28 mm as well as for many plastic and multilayer composite pipes. Thin-walled plastic pipe needs a support sleeve inside the pipe end; without it the olive simply crushes the pipe.
Where it is used
- Connecting radiators, taps and appliances — precisely because the joint can be undone again
- Repairs and alterations where soldering is not allowed or not practical, for example close to timber or insulation
- Transitions between materials, such as copper to multilayer pipe
- Temporary and test installations
Small sizes typically cost a few euros per fitting; larger diameters and quality brass fittings run higher.
Practical tips
- Cut square and deburr — a skewed or burred pipe end is the main cause of weeping joints; use a pipe cutter
- Use two spanners — hold the body while you tighten, or you twist the pipe and open the joint next along
- Do not overtighten — hand tight plus roughly half to one full turn is usually enough; going further cuts the olive into the pipe and causes the leak you were trying to avoid
- No tape or hemp on the compression face — the seal is the olive itself; sealing compounds belong only on tapered threads
- Do not bury them out of reach in walls or screeds: demountable joints should stay accessible, and concealed joints should be permanent (soldered or pressed)
- Never reuse an olive — once deformed it rarely seals cleanly a second time
Related terms
- Pipework
- Building services
- Radiator
- Drain-off valve
- Pressure pipe
- Welding
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