Abstract: A coupling for pipes having confronting ends with conical or flat outwardly extending flanges utilizes an elastomeric sealing ring which is placed between the flanges and a variable-diameter clamping device which is positioned to surround the flanges and has two radially inwardly divergent sidewalls each of which is adjacent the exposed side of one of the flanges. The conical radially inner portions of the sidewalls engage and penetrate into the external surfaces of the pipes in response to a reduction of the diameter of the clamping device, and any further reduction of the diameter entails a movement of progressively larger parts of radially outer portions of the sidewalls into engagement with the exposed sides of the adjacent flanges to bring about radial compression of a large portion of the sealing ring.