A device for passive pressure relief and for reducing the volume flow for an electromechanically driven medical gas delivery means (50) in a medical device for respirating a patient (60) with a pressure relief unit (1) with a first and second gas port (2, 3), with a relief valve (4), with a pressure relief outlet (8) with an equalization space (9) and with a nonreturn valve (11) and a valve disk (5), which is arranged in the relief valve (4) and is maintained in a position relative to a valve seat (7) via a bellows (60). The surfaces (51, 52) facing the first and second gas ports (2, 3) have different areas, so that the relief valve (4) opens as soon as an operating pressure (23) at the first gas port (2) exceeds a prevailing (stored) pressure level (24) in the equalization space (9).