The present invention provides a bypass system for respiratory therapy and anaesthesia comprising a first bypass conduit for receiving a gas flow and for receiving a filtration device. The bypass system also has an activation means for redirecting the gas flow within the first bypass conduit. A second bypass conduit for receiving the gas flow from the first bypass conduit and the filtration device is also present in the system. The bypass system also has a passive control valve within the second bypass conduit to redirect air flow within the second bypass conduit and a conduit interconnected to the first and second bypass conduit for providing a passage of gases between the first and second bypass conduit when activated by the activation means wherein the activation means is activated when the first bypass conduit is not connected to a filtration device.
