A relief valve assembly comprising: a main relief valve positioned adjacent a valve seat of a pressure vessel containing a sour gas, the main relief valve comprising: a main valve diaphragm selectively sealable against the valve seat of the pressure vessel, the valve diaphragm enclosing a valve dome containing an inert clean gas; and a hollow valve tube in pressure communication with the valve dome; and a pilot relief valve in pressure communication with the pressure vessel and the valve dome of the main relief valve, and having a pilot seat selectively sealable against the hollow valve tube, the pilot relief valve comprising: a biasing mechanism in communication with the pilot seat to urge the pilot seat toward sealed engagement with the hollow valve tube; and a sense diaphragm attached to the pilot seat and enclosing a sense cavity in pressure communication with the valve dome and the pressure vessel so that when a pressure in the pressure vessel exceeds a predetermined level, pressure within the sense cavity urges the sense diaphragm and the pilot seat away from the hollow valve tube, which in turn allows compression of the valve diaphragm so that it separates from the valve seat, thereby allowing sour gas to escape from the pressure vessel; and an equalizing line for sensing and substantially equalizing the pressure in each of the valve dome, the sense cavity, and the pressure vessel; the equalizing line providing fluid communication between a gas cylinder containing an inert clean gas, the valve dome, the sense cavity, and the pressure vessel. a main relief valve positioned adjacent a valve seat of a pressure vessel containing a sour gas, the main relief valve comprising: a main valve diaphragm selectively sealable against the valve seat of the pressure vessel, the valve diaphragm enclosing a valve dome containing an inert clean gas; and a hollow valve tube in pressure communication with the valve dome; and a pilot relief valve in pressure communication with the pressure vessel and the valve dome of the main relief valve, and having a pilot seat selectively sealable against the hollow valve tube, the pilot relief valve comprising: a biasing mechanism in communication with the pilot seat to urge the pilot seat toward sealed engagement with the hollow valve tube; and a sense diaphragm attached to the pilot seat and enclosing a sense cavity in pressure communication with the valve dome and the pressure vessel so that when a pressure in the pressure vessel exceeds a predetermined level, pressure within the sense cavity urges the sense diaphragm and the pilot seat away from the hollow valve tube, which in turn allows compression of the valve diaphragm so that it separates from the valve seat, thereby allowing sour gas to escape from the pressure vessel; and a main valve diaphragm selectively sealable against the valve seat of the pressure vessel, the valve diaphragm enclosing a valve dome containing an inert clean gas; and a hollow valve tube in pressure communication with the valve dome; and a pilot relief valve in pressure communication with the pressure vessel and the valve dome of the main relief valve, and having a pilot seat selectively sealable against the hollow valve tube, the pilot relief valve comprising: a biasing mechanism in communication with the pilot seat to urge the pilot seat toward sealed engagement with the hollow valve tube; and a sense diaphragm attached to the pilot seat and enclosing a sense cavity in pressure communication with the valve dome and the pressure vessel so that when a pressure in the pressure vessel exceeds a predetermined level, pressure within the sense cavity urges the sense diaphragm and the pilot seat away from the hollow valve tube, which in turn allows compression of the valve diaphragm so that it separates from the valve seat, thereby allowing sour gas to escape from the pressure vessel; and a biasing mechanism in communication with the pilot seat to urge the pilot seat toward sealed engagement with the hollow valve tube; and a sense diaphragm attached to the pilot seat and enclosing a sense cavity in pressure communication with the valve dome and the pressure vessel so that when a pressure in the pressure vessel exceeds a predetermined level, pressure within the sense cavity urges the sense diaphragm and the pilot seat away from the hollow valve tube, which in turn allows compression of the valve diaphragm so that it separates from the valve seat, thereby allowing sour gas to escape from the pressure vessel; and an equalizing line for sensing and substantially equalizing the pressure in each of the valve dome, the sense cavity, and the pressure vessel; the equalizing line providing fluid communication between a gas cylinder containing an inert clean gas, the valve dome, the sense cavity, and the pressure vessel.