Rotary feed-through

A rotary union (6) for a compressed air supply system is provided between a stator (1) and a rotor (3) rotating relative to it, wherein a compressed air channel (8) arranged in the stator (1) is connected to a compressed air line (7) and opens into an annular space (29) formed in the rotor (3), from which at least one working channel (44) leading to a consumer (5) emanates, and wherein the stator (1) in the region of the rotary union (6) is connected to a control line (21). The friction torque occurring in the region of the rotary union (6), which leads to a temperature increase at the sliding surfaces of its seal and to premature wear thereof, is to be reduced by arranging a switchable check valve (30) in the annular space (29), whose blocking elements (32 and 33) extend concentrically to the axis of rotation of the rotor (3) within the annular space (29) and are movable into an open position in this region via an actuating element (11) displaceable from the stator (1) in the direction of the blocking elements (32 and 33).