The 225-0040 Auto-Soft is a flow actuated, size NW40 check valve used for throttling roughing pumps during initial evacuation. Auto-Soft closes very quickly at the start of system evacuation and opens automatically upon reaching a set pressure differential. This leaves the pumping line open for the balance of the pumping process. Auto-Soft has a vane that pivots about an off-center axis. A pair of coil springs hold the vane open when the pressure differential is low enough. When the roughing system goes into operation, the initial flow closes the vane assembly, automatically throttling the roughing pump. Initial pumpdown occurs through small openings around the vane. This reduces the effective pumping speed, which minimizes turbulence and extends pumpdown time. When the pressure differential reaches the level determined by the springs, the springs open the vane and full pumping speed is restored. When installing the Auto-Soft, adequate space is needed, the amounts are listed in the specifications table. The user can adjust the closed conductance of the valve over a limited range by bending tabs adjacent to the vane. The Auto-Soft should be installed between the vacuum system and the roughing valve. Trapping of contamination before the Auto-Soft will help to ensure a long life.