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 comprising:
- a body having a first, longitudinal axis, a second axis transverse to said first axis, and inner walls about said first axis, said inner walls defining at least a piston chamber and a detent cavity;
- a shift rod adapted to interface with a valve actuator of said valve block, said shift rod having a central axis collinear with said first, longitudinal axis of said body and being translatable along said central axis between a first position with respect to said body and a second position with respect to said body;
- a first seal member about said shift rod, said first seal member forming a substantially fluid tight seal between said shift rod and said inner walls of said body to define a first end of said piston chamber;
- a second seal member about said shift rod, said second seal member forming a substantially fluid tight seal between said shift rod and said inner walls of said body to define a second end of said piston chamber;
- a floating piston slidingly affixed about said shift rod, said floating piston forming a substantially fluid tight seal between said shift rod and said inner walls of said body to segregate said piston chamber into a first volume adjacent said first end of said piston chamber and a second volume adjacent said second end of said piston chamber;
- a first shoulder about said shift rod within said first volume and adjacent said first end of said piston chamber, and a first piston spring between said first shoulder and said floating piston;
- a second shoulder about said shift rod within said second volume and adjacent said second end of said piston chamber, and a second piston spring between said second shoulder and said floating piston;
- a stop member fixed in place about said shift rod within said detent cavity, said stop member having a first groove and a second groove substantially identical to said first groove, wherein the central plane through said second groove is longitudinally spaced apart from the central plane through said first groove by a distance equal to the distance that said shift rod translates between said first position and said second position;
- a first detent having a spring biased catch, said spring biased catch being oriented along said second, transverse axis of said body and being adapted to conformingly engage with said first groove when said shift rod is in said first position with respect to said body and with said second groove when said shift rod is in said second position with respect to said body;
- a first fluid conduit from without said body to within said first volume, said first fluid conduit being in fluid communication with said first pressure port of said valve block;
- a second fluid conduit from without said body to within said second volume, said second fluid conduit being in fluid communication with said second pressure port of said valve block;
- and
- whereby 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 within said second volume of said valve controller reaches a threshold value below the fluid pressure within said first volume 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 within said first volume of said valve controller reaches a threshold value below the fluid pressure within said second volume of said valve controller.