The 253B-20-40-1 Exhaust Throttle Valve regulates the removal of gas from a processing system. It features a 0.779 inch (20 mm) nominal inside diameter and a size NW40 ISO-KF Flange. A flapper O-ring is included. Its flapper is positioned to modulate gas flow, thereby controlling process pressure. The 253 has a patented non-linear actuator placed between the flapper shaft and the motor drive shaft in order to generate a linear valve transfer characteristic and provide smooth linear pressure control. The Type 253 is available in standard sizes and flange styles, and is compatible with all MKS throttle valve controllers.