Pipe joint construction

Claim 1

In a pipe joint construction comprising a spigot having a taper surface on the outer periphery at the front end, a socket having a first projection on the inner periphery at the open end adapted to be loosely fitted over said spigot, an annular groove disposed adjacent the inner side of said first projection and a packing seat formed adjacent the inner side of said annular groove, and a packing having a back-up portion with a fitting portion projecting from its outer periphery for fittng in said annular groove and a seal portion adapted to be interposed in squeezed condition between said packing seat and the outer peripheral surface of the spigot, the inner peripheral surface of said packing tapering from the end edge of said back-up portion toward the seal portion, the improvement comprising: (a) said packing seat being formed as an internal cylindrical surface extending from said annular groove inwardly of the socket; (b) a secnd projection formed on the socket at the inner end of said packing seat and projecting toward the spigot; (c) a step surface provided on the socket in inwardly spaced relation to said second projection, said step surface being opposed to the front end of the spigot; (d) an annular seat provided in the outer peripheral surface of the spigot adjacent the front end thereof, a radially contractible lock ring fitted in said annular seat, said lock ring being disposed between said second projection and said step surface and being engageable with said second projection upon relative axial separating movement between the socket and spigot, and fastening means for preventing disengagement of said lock ring from said annular seat; (e) the socket having an inner peripheral surface extending axially from said second projection towards said step surface, said inner peripheral surface having a diameter such as to provide an annular clearance space with the outer periphral surface of the spigot for passage of said lock ring and such as to provide a radial clearance with the lock ring for relative bending movement between the socket and the spigot; (f) the axial length of said inner peripheral surface being equal to the sum of the distance between the front end of the spigot and the lateral surface of the lock ring opposed to said second projection and a distance provided for all allowable relative axial movement between the socket and the spigot; and (g) said inner peripheral surface of the packing tapering inwardly of the socket from a maximum diameter of at least equal to the inner diameter of said first projection to a minimum diameter on said packing seal portion which is compressively engaged by the outer periphral surface of the spigot.