A relief valve for anesthetic gas line which is spring loaded to conventionally discharge overloading anesthetic gas into the surrounding atmosphere, and which further is provided with a valve assembly for connection to a closed system so that the overloading anesthetic gas is retained with the closed system and is not discharged to the surrounding atmosphere. The open system of the valve is maintained by making the spring loaded valve operational, and the closed system is effected by closing the spring loaded valve so that overloading anesthetic gas is directed through the valve assembly into the closed system, preferably a surgical room vacuum line.