Abstract: A pressure relief valve (10) for a pilot operated fluid system (FIG. 4) for a pressure vessel (12). Pressure relief valve (10) has a valve body (14) forming a valve chamber (16) accessible by upper cover plate (24). A cylindrical housing (32) is mounted in the valve chamber (16). A valve stem (38) has a diaphragm assembly (40) on its upper end and a valve assembly (42) on its lower end. Diaphragm assembly (40) includes a rolling loop diaphragm (44) fitting between opposed surfaces (36, 60) of housing (32) and piston member (56). A circular guide (66) on valve stem (38) fits within housing (32) for guiding the movement of the valve stem (38). Valve assembly (42) is connected to valve stem (38) about a ball and socket joint formed by ball (70) on the valve stem (38) and a socket (84) on the valve assembly (42).