The MKS 656 Throttling Isolation Valves are designed on the platform of the industry standard MKS bellow-sealed angle and in-line valves. The Type 656 provides: 1) fast, accurate closed-loop control of process pressures; 2) positive leak-tight shutoff when closed; and 3) soft pumpdown from atmosphere. These valves are a simpler and less costly alternative to the combination of shutoff gate, butterfly control, and soft start valves. The valves are available in angle or in-line configurations in 40 mm, 50 mm, 80 mm, and 100 mm sizes (1.5, 2, 3, 4 inches). 656 Valves feature a patented, unique constant force closure that compensates for thermal expansion/contraction and seals leak-tight even under changing sealing conditions as encountered in many contaminant-prone processes.