A pressure valve including a valve seat 3 is mounted on a cap body 8 side. The cap body 8 and a filler neck 6 are fastened together in an anti-disengagement manner by use of locking means.

A welding structure for a fuel tank including a resin inner shell and a resin outer shell interposed by a fuel permeation prevention layer such that they are laminated, and a resin component attached to the fuel tank. The resin component includes a body formed from a resin having low permeability to hydrocarbon gases, a packing material having low permeability to hydrocarbon gases which is fixed to the body, and a resin which is insert molded to at least a connecting portion of the body that connects with a connecting portion of the fuel tank, and which can be welded to the fuel tank.

A polymeric tank assembly is provided having a polymeric container with a neck opening. A ring with protruding barbs is inserted within the neck opening and the neck opening is placed in compression by a surround collar. The ring can be connected with clamping arms which can be engaged by a clamping ring which retains an instrument within the tank assembly.

A fuel tank with an opening, on which a lid is mounted in a removable manner by means of thread or bayonet, is intended to provide a sustained and sealed closure under all conditions. For this purpose, two sealing rings are arranged between the sealing surfaces, the inner one being liquid-tight and the outer one being made of an elastomer with high permeation resistance. The sealing surfaces within the outer sealing ring have a narrow gap leading as far as the outer sealing ring, and the fuel tank has a reinforcement surrounding the opening.