Push-fit fitting

How the joint works[edit]

Two components do the work. The grab ring, a toothed stainless ring, resists the pipe being pushed back out under pressure. The O-ring, seated in a groove ahead of it, provides the seal against the outside surface of the pipe. Correct assembly requires the pipe to be cut square, deburred and inserted fully to the depth mark, so that the O-ring sits on clean, undamaged pipe wall rather than on a burr or a scored surface.

A pipe insert is required in plastic tube. It supports the bore against the compressive grip of the grab ring so the tube does not deform inwards and break the seal.

Failure modes relevant to leak work[edit]

Push-fit joints fail in characteristic ways, and the failures are relevant to leak detection because they are frequently concealed. Insufficient insertion depth leaves the O-ring on or near the cut end of the pipe, which may seal initially and fail later. A missing insert in plastic tube allows gradual deformation and a slow weep. A scored or scratched pipe surface gives the O-ring a leakage path along the scratch. O-rings also degrade over time with heat and with contact with unsuitable jointing compounds.

The result is often a very small, continuous loss rather than a burst, which is exactly the profile that produces steady pressure loss on a sealed heating system without visible damp.

Concealed joints[edit]

Because push-fit joints can be made quickly and without heat, they are sometimes used in positions where access is later lost, beneath floors, within screed or inside boxed voids. Where a concealed joint fails, detection rather than inspection is the only route to it, and tracer gas and acoustic methods are commonly used to fix the position before the covering is opened. ADI Leak Detection names borescope inspection and tracer gas against concealed pipework in walls, floors and ceilings.^[4]