an improved rotor retainer housing for a rotatable rotor body and a relief sealing mechanism for a gas flow rate regulator . the retainer housing having structural features equivalent to the essential corresponding features of a conventional metal part is formed of molded plastic . a thin metallic layer is provided on the exposed surfaces of the molded plastic part to enhance surface conditions for maintaining an effective seal between the retainer housing and associated parts . the relief sealing mechanism utilizes a separate relief valve and relief valve seal to prevent premature failure of the seal during normal operating pressures . the seal is a metal retaining ring having a polymer o - ring integrally formed within the retaining ring . the o - ring provides sealing surfaces between the relief valve and the gas inlet on the regulator .