Series 225 Auto-Soft
Check Valves for Automatic Soft Starts

photo - Series 225 AUTO-SOFT Flow-actuated Check Valve

The MKS Series 225 Auto-Soft is a flow actuated check valve used for throttling roughing pumps during initial evacuation. Auto-Soft check valves close very quickly at the start of system evacuation and open automatically upon reaching a set pressure differential. This leaves the pumping line open for the balance of the pumping process.

Features & Benefits:

  • Reduces particulate contamination by limiting turbulent flow
  • Replaces expensive pressure controlled bypass systems
  • Operates automatically without external power
  • Replaces ISO-KF centering ring for easy installation


In semiconductor, thin film, and other industries, Auto-Soft check valves replace pressure controlled bypass valves to provide a soft start and reduce turbulence in the vacuum system. On a system with a mechanical pump, Auto-Soft check valve can reduces exhaust oil mists.


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Part NumberPriceQTY
Series 225 AUTO-SOFT Check ValveQuote Only

Documents & Downloads:

Auto-Soft data sheet

Need help?

Contact an Application Specialist by sending an email to MKS Instruments or call 303-449-9861.