Pipes, Fittings and Jointing Methods
Pipes, Fittings and Jointing Methods tests whether you can select a joint for the material and make it leak-free. The exam includes threaded, solvent-cement, compression, push-fit, fusion and brazed joints, plus fitting allowances.
Jointing rules
- GI threaded: use tapered threads, PTFE tape or approved compound, engage 3–4 threads, do not overtighten.
- PVC/CPVC solvent: cut square, deburr, clean, apply primer, coat socket and spigot, insert with a quarter-turn, hold, then cure before pressure testing.
- Compression: cut square, insert the olive fully, tighten by hand then one turn; avoid over-tightening.
- Push-fit: mark insertion depth, clean the O-ring seat, insert fully; use the locking ring where specified.
- HDPE/PPR fusion: heat both faces to the correct temperature and time, join without twisting, allow to cool.
- Copper brazing: clean, flux, heat evenly, capillary fill; protect nearby surfaces.
Worked example
A measured run is 2.00 m between two elbow centres. Each elbow socket engagement is 20 mm. Cut length = 2.00 − 2(0.020) = 1.96 m. If the pipe is inserted fully, the finished centre-to-centre distance returns to 2.00 m. Always subtract fitting allowances before cutting.
Traps
Skipping primer, using excess cement, crossing threads, or pressure-testing before the solvent has cured causes failures. A compression joint that leaks is often under-tightened, not over-tightened.