Abstract: A system for the leaktight connection of a valve unit to a respective pipe, is provided. The valve unit includes a gas through-flow section, a threaded male attachment element being formed integrally with the valve unit and having an axial through cavity defining the gas through-flow section, for leaktight clamping by a pipe-fixing ring-nut connector which can be screwed onto the male threaded portion of the attachment element. The system includes a second leaktight connector which can be put into operation as an alternative to the ring-nut connector. The second connector including at least one axial retaining element which can be releasably restrained on the valve unit in the region of the threaded portion of the male attachment element, in a manner such that the pipe is restrained axially relative to the valve unit.