Testing, leak detection, maintenance and repair
Testing, leak detection and repair
This domain tests the sequence of pressure and drainage testing, how leaks are traced, and how repairs are made so they last.
Pressure testing
Test water lines before concealment. Fill slowly, expel air at the highest point, and pressurise to 1.5 times the working pressure, typically held for one hour with no visible leakage and no loss of pressure. Cap all outlets, isolate the pump, and use a calibrated gauge. Plastic lines must be left to cure - usually 24 hours after solvent cementing - before testing.
Drainage testing
Water test on the stack and house drain, air or smoke test to prove the traps and joints, and a ball test to confirm the drain is clear and falls correctly. Check every trap seal after testing.
Leak detection methods
Visual inspection for damp patches and staining, soap solution on compressed air lines, dye in tanks and cisterns, acoustic listening on buried mains, meter creep test with all taps closed, and thermal or moisture meters on concealed work.
Repairs
Cut out and replace a damaged section rather than patch it; use a repair clamp on a pinhole in a main, re-thread a corroded GI end or use a socket, solvent-weld a new PVC section with a coupling, repack a leaking valve gland, and replace a failed washer. Log every job on a maintenance card.
Worked example
A 25 mm line is tested at 6 bar; the gauge falls to 5.2 bar in 20 minutes with no visible wet patch. Reasoning: pressure loss means either a leak or trapped air. Bleed the air, re-pressurise; if it still falls, isolate sections with valves to locate the faulty joint, then repair and retest.
Traps that cost marks
Testing a solvent-cemented line immediately; air testing a pressure line; an uncalibrated gauge; testing after plastering; patching a crack instead of replacing the section.