purpose of protecting the cylinders only is fed to the enclosure 19 through a valve 17 which is a control valve for turning on and off the nitrogen supply valve 18 is a pressure reduction valve which reduces pressure to a low level such as two or three inches water column in order to provide a very slight positive pressure within the enclosure with respect to the mine ambient pressure this pressure in the enclosure is controlled by sizing orifices 31 in the upper flange as well as valves on the inlet and or adjustable valves at the outlets for example an r400 regulator manufactured by maxitrol can be used to provide an outlet pressure of four inches water column at the lower flange to provide a 100 cubic foot per hour flow rate with an exhaust velocity of 10 feet per second a total area of 0 4 square inches for the exhaust ports can be used eight quarter inch diameter holes will provide an appropriate size the enclosure 19 may be made of a flexible plastic material with a sealable longitudinal split which runs vertically along one side this enables the enclosure along with the upper flange 30 and the lower flange 32 to be wrapped around the hydraulic cylinder 21 without removal of the hydraulic cylinder 21 from the roof support assembly 10 this system and apparatus provides for protection against hydrogen sulfide corrosion.