Abstract: A composite pressure vessel comprised of an inner fluid tight liner and an outer reinforced polymer layer. An end boss comprising a short pipe section arranged through an opening of the vessel and extending to a lower end with an outwardly extending flange on the pipe section arranged between the outer layer and the inner liner, and a lid arranged at an upper end of the pipe section. The inner liner extends upwards through the opening of the pipe section to the lid with at least one gas tight seal interfacing against the inner liner. A pre-tensioning device is arranged on the outside of the inner liner, in a groove nearest to the lid and pipe section, around the upper end of the pipe section, which, regardless of the pressure in the vessel, presses the inner liner against the at least one gas tight seal.

Abstract: End boss (2,9) arranged in an opening of a composite pressure vessel comprising an inner fluid tight liner (3) and an outer reinforced polymer layer (1), which end boss comprises a short pipe section (2) and a lid (9), the lid is arranged at an upper end of the pipe section (2) that extends outwards from the vessel, the pipe section (2) is arranged through the opening of the vessel and extends to a lower end where an outwardly extending flange on the pipe section is arranged between the outer reinforced polymer layer (1) and the inner liner (3) in the vessel, distinguished in that the inner liner (3) extends upwards through the opening of the pipe section to said lid, on the inside of the inner liner, in a distance nearest to the lid, a sealing surface is arranged, the sealing surface lies against the inner liner and has at least one gas tight seal interfacing against the inner liner as the sealing surface is integrated with the lid or is a sleeve or a pipe section which is sealingly fastened to the lid, a