A flow regulating valve for a respiratory treatment system is disclosed, as well as a vent arrangement comprising the flow regulating valve. The flow regulating valve may include an inlet, an outlet, and a variable conduit in fluid communication with the inlet and the outlet. The variable conduit may include a movable portion that may move to vary an impedance of the variable conduit, thereby regulating a flow rate of the air travelling through the variable conduit. Advantageously, the flow regulating valve may thus reduce wastage of air (e.g. humidified air) that is exhausted from a respiratory treatment system, while maintaining sufficient washout of air.