a pressure relief valve includes a two - piece housing having therein a generally circular diaphragm backed by a spring biased plate . the outer edge of the diaphragm is captured between the two pieces of the housing and to provide a first sealing area . the central portion of the diaphragm has a circular opening therein with an annular sealing lip formed thereabout . the sealing lip provides a seal when the spring biased plate moves the diaphragm against a flat circular seat . when pressure at the inlet of the housing overcomes the spring biasing force , the diaphragm is moved away from the seat and the gas is relieved through an outlet in the housing .