A pneumatic arrangement for continuous delivery of a volumetrically proportioned mixture of gases, said pneumatic arrangement comprising:
- a first pressurized gas source and a second pressurized gas source;
- a first set of storage vessels and a second set of storage vessels, wherein:
- said first set of storage vessels includes a first vessel having a first volume and a second vessel having a second volume;
- said second set of storage vessels includes a third vessel having a third volume and a fourth vessel having a fourth volume;
- and
- the ratio of said third volume to said fourth volume is substantially equal to the ratio of said first volume to said second volume;
- a valve block, said valve block having:
- a first source gas inlet in fluid communication with said first pressurized gas source, and a second source gas inlet in fluid communication with said second pressurized gas source;
- a first vessel gas passage in fluid communication with said first vessel, a second vessel gas passage in fluid communication with said second vessel, a third vessel gas passage in fluid communication with said third vessel, and a fourth vessel gas passage in fluid communication with said fourth vessel;
- a mixed gas outlet;
- and
- a first pressure port and a second pressure port;
- and
- wherein:
- said valve block is selectively operable in a first valve state and a second valve state;
- said first valve state establishes:
- a first fluid interconnection between said third vessel gas passage, said fourth vessel gas passage, said mixed gas outlet, and said second pressure port;
- a second fluid interconnection, isolated from said first fluid interconnection, between said first source gas inlet and said first vessel gas passage;
- a third fluid interconnection, isolated from both said first fluid interconnection and said second fluid interconnection, between said second source gas inlet and said second vessel gas passage;
- and
- a fourth fluid interconnection between said first pressure port and a single one fluid interconnection selected from the group consisting of:
- said second fluid interconnection of said first valve state;
- and
- said third fluid interconnection of said first valve state;
- and
- said second valve state establishes:
- a first fluid interconnection between said first vessel gas passage, said second vessel gas passage, said mixed gas outlet, and said first pressure port;
- a second fluid interconnection, isolated from said first fluid interconnection, between said first source gas inlet and said third vessel gas passage;
- a third fluid interconnection, isolated from both said first fluid interconnection and said second fluid interconnection, between said second source gas inlet and said fourth vessel gas passage;
- and
- a fourth fluid interconnection between said second pressure port and a single one fluid interconnection selected from the group consisting of:
- said second fluid interconnection of said second valve state;
- and
- said third fluid interconnection of said second valve state;
- and
- a valve controller operably interfaced with said valve block, said valve controller having a first pressure port in fluid communication with said first pressure port of said valve block, and a second pressure port in fluid communication with said second pressure port of said valve block, and wherein said valve controller;
- is adapted to cause said valve block to transition from said first valve state to said second valve state when the fluid pressure at said second pressure port of said valve controller reaches a threshold value below the fluid pressure at said first pressure port of said valve controller;
- is adapted to cause said valve block to transition from said second valve state to said first valve state when the fluid pressure at said first pressure port of said valve controller reaches a threshold value below the fluid pressure at said second pressure port of said valve controller;
- and
- comprises a positive actuation mechanism adapted to ensure full completion of any initiated transition between said valve states.