Compare Description Drawings, CAD & Specs Availability Price
225 auto-soft flow actuated check valve
Check Valve, Flow Actuated, NW40 Size, Auto-Soft
4 Weeks
4 Weeks
225 auto-soft flow actuated check valve
Check Valve, Flow Actuated, NW50 Size, Auto-Soft
2 Weeks
2 Weeks


  • Type
    Check Valve for Automatic Soft Starts
  • O-ring
  • Operating Temperature
    100°C max.
  • Tube Outer Diameter
    NW40, NW50
  • Required Clearance
    0.3 - 1.0 inches, depending on configuration
  • Spring Material
  • Closing Flow
    NW40: 6 CFM/sec, NW50: 12 CFM/sec
  • Ring, Tabs, Stop & Axel Material
    Type 304 stainless steel
  • Vane Material
    Inconel® 625
  • Bearing Material
  • Closing Time
    NW40: 10 ms, NW50: 12 ms
  • Opening Pressure
    NW40: 2 Torr, NW50: 3 Torr
  • Pumpdown Time
    Typical increase in pumpdown time is 3 times.
    Times were measured using a pump capacity of 27 CFM for NW 40, 70 CFM for NW 50 and a volume of 100 liters.


Automatic Soft Starts

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.


In the semiconductor, thin film, and other industries, Auto-Soft replaces pressure controlled bypass valves to provide a soft start. The soft start then reduces turbulence in the vacuum system. Particles resident in the system are not stirred up and the work in progress is not damaged. During pumpdown, the pressure differential across products in the system can displace or break them. Auto-Soft slows the pumpdown process, eliminating the wide pressure differential. Auto-Soft can be used when venting a system. Used with a vent valve, Auto-Soft will reduce turbulence and extreme pressure differentials while venting the system. Auto-Soft can be used in many other applications. When used with potting compounds, Auto-Soft prevents excessive foaming. Auto-Soft used in a vacuum glove box avoids the rupture of filters. When used on a system with a mechanical pump, Auto-Soft reduces exhaust oil mists.

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