Plumbing
What this domain tests
Plumbing questions cover pipe materials and sizes, jointing methods, cold-water distribution from an overhead tank, valves and fixtures, and pressure testing before concealment.
Core rules and concepts
- GI medium-class pipe for exposed cold water lines; CPVC for hot water; UPVC or SWR for drainage; HDPE for underground water mains.
- Nominal bores: 15 mm for taps and bib cocks, 20-25 mm for branch lines, 32-50 mm for main distribution and risers.
- Fittings: elbow, tee, reducer, union, nipple, socket; controls include stop cock, gate or ball valve, bib cock, float valve in the tank, water meter and ferrule at the mains.
- Jointing: GI pipes are threaded with hemp or PTFE tape; CPVC and UPVC use solvent cement with a clean, square-cut end; never mix dissimilar metals without a dielectric union.
- Layout: overhead tank, downpipe, distribution manifold, then branch to each fixture, keeping the tank outlet above the highest fixture.
- Hydraulic test at 1.5 times the working pressure for about one hour before pipes are buried or chased; drainage pipes are tested by water filling.
Worked example
Storage for a household. Five persons at 135 litres per person per day = 675 litres, plus one day's reserve if supply is intermittent, gives about 675-1000 litres. A 1000-litre HDPE tank covers the demand and allows for cleaning downtime, provided the roof slab and supporting platform are checked for the full water load of about 1000 kg.
Traps that cost marks
Using a 15 mm branch for a WC flush pipe; leaving no air gap or overflow in the tank; forgetting the test pressure rule and burying untested pipework; ignoring the water seal requirement of the connected sanitary fitting.