Zero dead-leg gas control apparatus and method

A device for controlling the flow of process gas from a source of said gas to a utilization location, said device comprising in combination,

• a gas flow conduit for conducting process gas from a process gas source towards said utilization location,
• a valve structure in said gas flow conduit,
• said valve structure having a gas passageway in the form of a continuous loop, said passageway having first, second and third ports spaced apart from one another;
• a pair of valve closure members positioned adjacent said continuous loop, each being mounted adjacent one of said first and second ports and being movable to open and close the port to which it is adjacent;
• and
• an actuating device for selectively actuating said valve closure members to selectively open and close said first and second ports for communicating said process gas to said utilization location;
• in which said continuous loop extends from said third port past said first port and then past said second port and then back to said third port, and in which said valve closure members selectively allow said process gas to flow through one of said first and second ports, through said continuous loop and through said third port to prevent dead leg spaces within said continuous loop,
• a process gas supply conduit connected to one of said ports,
• a purge gas supply conduit connected to another of said ports, and
• a vacuum supply conduit connected to said valve structure whereby gas can be supplied selectively to said gas flow conduit from at least one of said process gas supply and said purge gas supply, and can be evacuated from said gas flow conduit by said vacuum supply.