(under subclass 552) Apparatus wherein the information conveyed by the indicators is in some code not obvious to an uninformed operator, whereby the operation is similar to that required by combination locks in that the indicators must be positioned in a predetermined relationship to allow flow through the system.
SEE OR SEARCH THIS CLASS, SUBCLASS:
383+, for apparatus including a lock or seal.
613+, for mere serial valves in a single flow path.
