pipes 14 and 15 each internal bore 19 is normally intermediately occluded by a rupture disc 21 to prevent flow therethrough to the vent pipes 14 and 15 respectively a locking mechanism 23 secures the rupture disc 21 within the cartridge 18 and sealing rings 24 and 25 prevent leakage of fluids past the cartridge 18 into the ambient atmosphere while particular relief devices 4 and 5 have been illustrated a conventional rupture disc assembly relief valve or the like could be utilized for the same purpose the valve mechanism 3 comprises a housing 30 having the inlet port 12 located therein as seen in fig3 the housing 30 includes a lower portion 32 and an upper portion 33 the upper portion 33 is joined with the lower portion 32 by suitable bolts 35 or the like a chamber 38 is formed within the housing 30 an inner surface 39 of the housing upper portion 33 is defined by rotation of a shape about an axis 41 which is generally symmetrical and smoothly curved in the illustrated particular embodiment shown in fig3 the surface 39 is generally hemispherical in shape except for openings therethrough which will be discussed herein below a first port 43 and a second port 44 pass through the housing upper portion 33 and open onto the surface 39 so as to communicate the chamber 38 with central bore 19 of the relief devices 4 and 5 respectively the ports 43 and.