The invention relates to a valve assembly of a pipe disconnector for separating a service water system which is arranged to be filled or re-filled from a drinking water system, comprising upstream and downstream backflow preventers which both close in the direction from the service water system to the drinking water system, and a relief valve, which is exposed to the pressure of the drinking water system in closing direction and which is adapted to connect the space between the backflow preventers to a drain, when this pressure ceases. A pipe disconnector is to be provided, which is easy to clean and to service. Furthermore, a valve assembly is to be provided which can be used equally for pipe disconnectors of the type CA and for pipe disconnectors of the type BA. This is achieved in that the backflow preventers and the relief valve are combined to form a structural unit which is designed to be removed from and set in, as a whole, into a pipe disconnector casing having connections for drinking water and service water and the drain. The relief valve comprises a slide valve body, which, at one end face, is exposed to the drinking water pressure and, at the opposite end face, is exposed to the pressure in a space between the backflow preventers, and which is arranged to cover, in its closed position, a lateral outlet opening of the pipe disconnector casing, which opening communicates with the outlet.