Downstream Vacuum Regulator, Sliding Gate Seat; 1/2″ – 2″ (DN15 – DN50) The Mark 65 Series is ideal for steam, water, oil, gas, air and chemical services. The vacuum pressure regulators control very accurately and shutoff tightly to maintain the proper vacuum setting. They are used to maintain vacuums at predetermined settings and to regulate vacuum on evaporators, cookers, grinding fixtures, milling machines, altitude chambers and other vacuum systems.