A switch valve for a hydraulic unit, in particular a quick-acting valve for a hydraulic unit of a hydraulically variable valve gear of a reciprocating internal combustion engine, having a valve body, which is guided in an axially movable manner in a housing part and which is sealed with respect to the housing part by a seal, wherein the seal is designed as a flat seal element, which encloses the valve body in a sealing manner and which is operatively connected to an axial surface of the housing part in a sealing manner.