A pressure regulator housing assembly comprising: a lower housing and an upper housing adapted for assembly via axial engagement and relative rotation; a plunger and diaphragm assembly supported within the lower and upper housings, said plunger movable toward and away from a valve seat, and said diaphragm having a radially inner edge fixed to one end of the plunger and a radially outer edge clamped between an annular surface within said upper housing and a surface of a clamp ring; wherein an outer peripheral surface of said clamp ring is formed with a first plurality of vertically-oriented, tapered teeth and an inner peripheral wall portion of said upper housing adjacent said annular surface is formed with a second plurality of vertically-oriented teeth engageable, on assembly, with said first plurality of vertically-oriented teeth thereby locking said clamp ring against rotation relative to said upper housing; and further wherein an inner peripheral surface of said upper housing is formed with circumferentially-spaced locking pads and an outer peripheral surface of said lower housing is formed with circumferentially-spaced locking recesses which, on axial assembly of the upper housing over the lower housings, are offset from said circumferentially-spaced locking pads and which upon relative rotation between said upper and lower housings, are seated in said circumferentially-spaced locking recesses to thereby lock said upper housing to said lower housing, and wherein during said relative rotation, said diaphragm rotates with said upper housing and an upper edge of said lower housing is engaged by a lower surface of said clamp ring. a lower housing and an upper housing adapted for assembly via axial engagement and relative rotation; a plunger and diaphragm assembly supported within the lower and upper housings, said plunger movable toward and away from a valve seat, and said diaphragm having a radially inner edge fixed to one end of the plunger and a radially outer edge clamped between an annular surface within said upper housing and a surface of a clamp ring; wherein an outer peripheral surface of said clamp ring is formed with a first plurality of vertically-oriented, tapered teeth and an inner peripheral wall portion of said upper housing adjacent said annular surface is formed with a second plurality of vertically-oriented teeth engageable, on assembly, with said first plurality of vertically-oriented teeth thereby locking said clamp ring against rotation relative to said upper housing; and further wherein an inner peripheral surface of said upper housing is formed with circumferentially-spaced locking pads and an outer peripheral surface of said lower housing is formed with circumferentially-spaced locking recesses which, on axial assembly of the upper housing over the lower housings, are offset from said circumferentially-spaced locking pads and which upon relative rotation between said upper and lower housings, are seated in said circumferentially-spaced locking recesses to thereby lock said upper housing to said lower housing, and wherein during said relative rotation, said diaphragm rotates with said upper housing and an upper edge of said lower housing is engaged by a lower surface of said clamp ring.