Which one of the circuits does not have valves?
Magills circuit
Bains circuit
Closed circuit
Mapleson E
Ayre's T-piece was invented by Phillip Ayer in 1937. This consists of a light metal tube 1 cm in diameter, 5 cm in length with a side arm. Used as such, it functions as a non-rebreathing system. Fresh gas enters the system through the side arm and the expired gas is vented into the atmosphere and there is no rebreathing.
Anesthesia Circuit