Abstract: A pressure regulator housing assembly includes a lower housing and an upper housing; a plunger and diaphragm assembly supported within the lower and upper housings, the plunger movable toward and away from a valve seat. The diaphragm has 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 locked against rotation relative to said upper housing thereby isolating said diaphragm from any contact with the lower housing. Upon assembly of the upper and lower housings requiring relative rotation therebetween, an upper edge of the lower housing is engaged by a lower surface of the clamp ring.