DE3011621

A gas flow unit such as a vaporiser mountable on a gas administration apparatus such as an anaesthesia machine in plug-in fashion includes an interlock system which prevents a valve for controlling the admission to the unit of gas from a supply provided by the apparatus from being operated before a locking mechanism has locked the unit to the anaesthesia machine. The interlock system also includes actuating means which, when the unit is mounted on the anaesthesia machine, opens respective valve members in ports located on the anaestheia machine only when the control valve is moved to its operating position. In the case when two similar units are mounted side-by-side on the anaesthesia machine and intended for use as alternatives, the interlock system includes pins which when the control valve on one unit is moved to its operating position, extend outwardly from the unit to prevent the control valve on the other unit from being operated.