Adapter for plastic pipe

Claim 1

An adapter for connecting a threaded metal element to a non-metallic pipe and providing a fluid-tight connection in a high-pressure system, comprising: a tubular plastic adapter unit having an open-ended bore at one end for telescoping with the non-metallic pipe, an internal annular shoulder facing toward the opening end of said bore, and a stepped internal passageway extending from said bore through the adapter unit to the opposite end thereof, said passageway comprising a first portion adjacent said opposite end having a first internal annular shoulder at its inner end spaced inwardly from said opposite end, a second portion smaller than said first portion having a second internal shoulder at its inner end, and a third portion smaller than said second portion between said second shoulder and said bore, and a ridge projecting inwardly from the wall of said passageway where said third portion meets said bore; and a tubular metal insert disposed in said passageway and having an internally threaded end portion fitted in said first portion of said passageway and having an external shoulder pressing against said first internal shoulder, an elongated cylindrical end portion extending through said second and third portions of said passageway to said ridge, and an outwardly flared end of said cylindrical portion within said bore curving around said ridge and pressing against the ridge to lock the insert within the adapter unit; an O-ring seal encircling said cylindrical end portion and positioned within said second portion of said passageway between said external shoulder and said second internal shoulder to form a fluid seal between said adapter unit and said insert; and interfitting longitudinal keying means on the wall of said passageway within said third portion and on said end portion for preventing relative rotational movement of said adapter unit and said insert.