Direct Operated Tank De-pad Regulator or Gas Back Pressure Regulator for low pressures 3/4″ – 2″ (DN20 – DN50) The Mark 508 Series gas back pressure regulator is the ideal valve for low back pressure gas services. The Mark 508 works in conjunction with the Mark 608, in a low pressure tank blanketing valve system. The Mark 508 can be used to vent gas from the tank to prevent the blanketing pressure from rising to a level that could damage the tank while maintaining a small constant flow to keep the blanket fresh. It will also work well in any other type of low back pressure application.