A relatively low pressure 
inert gas 
hazard suppression 
system (20) is provided which is designed to protect a room (22) or the like from the effects of fire or other 
hazard. The 
system (20) includes a plurality of pressurized 
inert gas cylinders (24) each equipped with a valve unit (26); each valve unit (26) is in turn coupled via a conduit (28) to a delivery manifold (30). The respective valve units (26) are operable to deliver gas from the cylinders (24) at a generally 
constant pressure (usually around 10-100 bar) throughout a substantial portion of the time of gas delivery, to thereby provide effective 
hazard suppression without the need for expensive high-pressure gas handling and distribution hardware and a reduction in room venting area due to lower room over-pressurization. Each valve unit (26) has a valve body (48) and a shiftable 
piston-type sealing member (56). 
Gas pressure from the cylinder (24) and a spring 
assembly (184) biases the member 56 to the valve open position, this being counterbalanced by 
gas pressure within 
equalization and modulation chambers (180, 182) provided in the valve unit (26). When a hazard is detected, the valve units (26) are actuated by draining of gas from the modulation chambers (182), allowing gas flow from the cylinders (24). As gas 
discharge proceeds, gas flows into and out of the modulation chambers (182) so as to achieve the desired generally 
constant pressure gas output. Near the end of gas 
discharge, the spring 
assembly (184) becomes predominant and holds the valve unit (26) open until all gas is discharged.