A plug-in coupling for connecting a tube to a pipe

A coupling device which separably connects the end of a hose to the end of a pipe has a sleeve one end portion of which is connectable to the end of the hose and the other end portion of which has axially parallel resilient radially movable prongs serving to establish a form-locking connection with an external rib on the end of the pipe in response to insertion of the end of the pipe into the other end portion of the sleeve. A locking ring which is reciprocable on the sleeve between a retracted position and an operative position has axially parallel arms which overlie the prongs in the operative position of the ring. A C-shaped indicator of the condition of the form-locking connection has tongue-like male detent members which extend into sockets provided therefor in the prongs when the ring is held in the retracted position and the end of the pipe is not in form-locking engagement with the prongs of the sleeve. The detent members are expelled from their sockets in response to form-locking engagement between the pipe and the sleeve, and the indicator is thereupon displaced longitudinally of the sleeve in response to movement of the ring to its operative position.