A proper breathing system is the corner stone for the oxygenation and for the delivery of anaesthetics to the patients during surgery. Various types of circuits are used for this purpose. Mapleson B circuit is one among it. Its use is discontinued for its inefficiency in the past. Hunt for a new breathing system will never end till the invention of a universal breathing circuit which can be used in all age groups and in both the types of ventilations. We have modified the Mapleson B circuit by introducing a unidirectional valve.  This modified Mapleson B system is functionally comparable with Bain’s circuit and closed circuit.