A bypass system for respiratory therapy and anaesthesia having a first bypass conduit for receiving a gas flow and for receiving a filtration device. The bypass system also has an activation device for redirecting the gas flow within the first bypass conduit. A second bypass conduit is also present in the bypass system which has a passive control valve to redirect air flow within the second bypass conduit. A conduit interconnects the first and second bypass conduit for providing a passage of gases between the first and second bypass conduits.
