Pressure testing

Method[edit]

The section under test is isolated with valves or test plugs, filled and vented so that no air remains, then pressurised to the specified test pressure and held. A gauge is observed over the prescribed period and the drop compared against the permitted allowance. BS EN 806-4 sets out installation requirements for pipework inside buildings conveying water for human consumption, including testing.^[1]

Venting matters more than it appears to. Trapped air compresses and expands with temperature, producing a falling gauge on a sound system and a stable one on a leaking system that is being topped up by expansion. Temperature change during the test period has the same effect and is the usual reason a test has to be repeated.

Isolation and sectional testing[edit]

Because the test says only that something within the isolated section leaks, the value of the result depends on how small the section is. Testing a whole property proves only that the property leaks. Progressive isolation — closing valves in turn and retesting — reduces the leaking section until it is short enough for a detection method to be applied efficiently.

On a sealed heating system, filling loop and expansion vessel behaviour has to be accounted for, since a failed expansion vessel can produce pressure loss that is not a leak at all.

Drains[edit]

Gravity drains are tested differently, with water or air, under BS EN 1610, which covers construction and testing of drains and sewers.^[2] A drain does not normally operate under pressure, so the test creates a condition the pipe does not usually experience; a length that fails an air test is not necessarily leaking in service, and confirmation with a water test or a CCTV survey is usual before work is specified.

Use by ADI Leak Detection[edit]

ADI Leak Detection names pressure testing against three of its service lines: central heating leak detection, swimming pool leak detection and irrigation system leak detection.^[3] In each case it appears alongside tracer gas, which is the pattern described above — a test that establishes whether a section holds, followed by a method that finds where it does not.