The performance of a scavenging valve.

A simple, compact and lightweight device for coupling active scavenging systems to shrouded breathing system valves is described. Provided a scavenging minute flow rate greater than the expired gas volume is available, the unit can handle automatically changes in both variables. Optimal function is achieved with scavenging flows from about twice the discharged gas flow to about 50 litre min-1. At these flows the valve can accommodate the outflow of gas-driven ventilators where driving gas and circuit gas are discharged through the same port. There is no interference with expiratory valve function in the event of scavenging failure.