Abstract: A snap-closure coupling for flowing medium ducts has two halves one of which can be plugged into the other. The arrangement is such that the flow paths through both the plug half (which is connected to a medium source) and through the socket or sleeve half (which is connected to a reservoir, such as the applied brakes of a trailer) will be blocked when the plug half is pressureless and the sleeve half is pressurized. However, when the plug half is inserted into the sleeve half, the flow paths through both halves are automatically opened.

Abstract: A socket valve of a quick-coupling for fluid lines under pressure has a sliding sleeve into an end recess of which a portion of a plug valve of the coupling is insertable, to be held by locking means. The sleeve is movable between a securing position in which it holds the locking means in locking position, and two axially displaced release positions in which it permits the locking means to release the plug valve. The sleeve is spring-biased to the securing position. As an additional safety factor, the sleeve is surrounded by an annular chamber at least one open end of which receives an annular piston. The chamber is communicated with the pressure fluid in the valve so that, when the sleeve is in the securing position, the fluid pressure biases the piston to a position in which it prevents accidental uncoupling of the plug valve, even in the event the biasing spring for the sleeve should break.