A device for detecting the condition of flow in a respiration system combines the function of a nonreturn valve with the function of flow measurement in a common device. The device includes a valve arrangement (1) with a valve disk (9) and with a valve body (8), wherein the position of a valve disk (9) in relation to a valve seat (11) is detected. An indicator for a flow and a direction of flow (5), (6) is determined from the position of the valve disk (9). The position of the valve disk (9) can be determined inductively, electrically, electromechanically or optically. The flow and direction of flow (5), (6) determined can be used to control the respiration in a medical device.
