A check valve comprises a housing (1) on which at least two connecting sleeves (2, 3) are provided, at least one valve seat (4) arranged in one of the connecting sleeves (3), and a valve body (6) which co-operates with the valve seat and
wich can be externally actuated by a control element (7). The check valve is to be versatile, so that pressure can be applied to it on both sides for example. To this end, the valve seat (4) has at least two seating surfaces arranged on opposite
sides of its narrowest cross-section (5), while the valve body (6) has at least two sealing surfaces which surround and co-operate with the seating surfaces of the valve seat (4). One sealing surface of the valve body (6) has a predetermined
diameter which is greater than the narrowest cross-section (5) of the valve seat (4), while the second sealing surface is expandable; when unexpanded, its diameter is less than the narrowest cross-section (5) of the valve seat (4) and when expandedm
its diameter is greater than the narrowest cross-section of the valve seat (4).
