A swivel-spout mixer tap seals the rotating joint between spout and body with an elastomeric O-ring seated in a machined groove, which is compressed radially against the bore to form a dynamic seal that must remain watertight while permitting rotation. Leakage at that joint is diagnosed as loss of the O-ring's compression set — the ring deforms, flattens, or extrudes over time — and is distinguished from valve-seat or cartridge failure, which manifests as flow with the tap handles closed. The topic belongs to domestic sanitary plumbing within building services, and applies the general sealing-element theory of grooved elastomeric seals, interchangeability by dimensional specification rather than by brand, and isolation requirements determined by whether the joint being opened lies upstream or downstream of the shutoff valve.
A swivel-spout mixer tap seals the rotating joint between spout and body with an elastomeric O-ring seated in a machined groove, which is compressed radially against the bore to form a dynamic seal t…