Abstract: This invention relates to a valve arrangement (8, 18) arrangeable to be used in a rebreathing system (1), said rebreathing system (1) comprising an oxygen supplying member (5, 15), a breathing mask (4, 14), a gas reconditioning unit (3, 13) where carbon dioxide in the exhaled gas is absorbed, a counter lung (2, 12) and a breathing passage (42, 142), wherein said valve arrangement (8, 18) is arrangeable to be used in a back and forth (two way?) breathing passage (42, 142) between said counter lung (2, 12) and said breathing mask (4, 14) of said rebreathing system (1), said valve arrangement (8, 18) containing an oxygen supply arrangement arranged to supply oxygen to the breathing passage (42, 142) provided that a predetermined level of oxygen pressure is exerted on said supply arrangement from said oxygen supplying member (5) and arranged to close the breathing passage when said oxygen supply pressure is below a predetermined level.