A vacuum-actuated valve assembly, comprising: a bellows defined at least in part by an enclosed chamber sealed to isolate said chamber from an outside region surrounding the bellows, said bellows comprising side regions configured to longitudinally expand in response to a predetermined vacuum condition surrounding the outside region of the bellows, said bellows having a top portion threadably engaged to a port body along an outer diameter of the bellows, and said bottom portion of the bellows substantially defined by a contact plate; a pin having a top end extending towards the bottom portion of the bellows and a bottom end extending through an opening of a stationary thermoplastic seat and an opening in a top portion of a stabber to contact a surface of the stabber; the stationary seat consisting essentially of a thermoplastic material and further wherein said thermoplastic seat is characterized by the absence of elastomeric material, said stationary seat comprising the opening extending from an outer surface of the seat to an inner sealing surface of the seat, said seat further comprising a grooved region extending along said inner sealing surface of said stationary seat; the stabber comprising a body portion and the top portion each of which is situated within the interior of the stationary seat, said interior of the stationary seat defined, at least in part, by an inner diameter greater than an outer diameter of the top portion and an outer diameter of the body portion thereby creating a passageway between the stabber and the seat; wherein said top portion of the stabber is engaged within said grooved region of the stationary seat so as to be maintained in mechanical engagement therealong when the bellows is in a non-expanded state, said engagement creating a seal that blocks the passageway and prevents the flow of fluid therethrough, thereby creating a closed configuration of the valve assembly; wherein expansion of the bellows along the side regions in a longitudinal direction in response to the predetermined vacuum condition surrounding the outside region of the bellows increases the length of the side regions of the bellows by an incremental amount sufficient to urge the contact plate downward against the top end of the pin, thereby causing said bottom end of the pin to push down against the surface of the stabber and disengage the top portion of the stabber from within the grooved region along the inner sealing surface of the stationary seat, thereby mechanically disengaging the seal to unblock the passageway and create a gap between the top portion of the stabber and the inner sealing surface of the stationary seat to create an open configuration of the valve assembly for the fluid to pass therethrough. a bellows defined at least in part by an enclosed chamber sealed to isolate said chamber from an outside region surrounding the bellows, said bellows comprising side regions configured to longitudinally expand in response to a predetermined vacuum condition surrounding the outside region of the bellows, said bellows having a top portion threadably engaged to a port body along an outer diameter of the bellows, and said bottom portion of the bellows substantially defined by a contact plate; a pin having a top end extending towards the bottom portion of the bellows and a bottom end extending through an opening of a stationary thermoplastic seat and an opening in a top portion of a stabber to contact a surface of the stabber; the stationary seat consisting essentially of a thermoplastic material and further wherein said thermoplastic seat is characterized by the absence of elastomeric material, said stationary seat comprising the opening extending from an outer surface of the seat to an inner sealing surface of the seat, said seat further comprising a grooved region extending along said inner sealing surface of said stationary seat; the stabber comprising a body portion and the top portion each of which is situated within the interior of the stationary seat, said interior of the stationary seat defined, at least in part, by an inner diameter greater than an outer diameter of the top portion and an outer diameter of the body portion thereby creating a passageway between the stabber and the seat; wherein said top portion of the stabber is engaged within said grooved region of the stationary seat so as to be maintained in mechanical engagement therealong when the bellows is in a non-expanded state, said engagement creating a seal that blocks the passageway and prevents the flow of fluid therethrough, thereby creating a closed configuration of the valve assembly; wherein expansion of the bellows along the side regions in a longitudinal direction in response to the predetermined vacuum condition surrounding the outside region of the bellows increases the length of the side regions of the bellows by an incremental amount sufficient to urge the contact plate downward against the top end of the pin, thereby causing said bottom end of the pin to push down against the surface of the stabber and disengage the top portion of the stabber from within the grooved region along the inner sealing surface of the stationary seat, thereby mechanically disengaging the seal to unblock the passageway and create a gap between the top portion of the stabber and the inner sealing surface of the stationary seat to create an open configuration of the valve assembly for the fluid to pass therethrough.