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Soft Start Check Valves (KF flanged)

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Used for throttling roughing pumps during their initial evacuation.

  • Flow actuated
  • 304 stainless steel construction
  • Reduce turbulence in a system by extending the pumpdown time*
  • Ideal for applications (semiconductor, thin film, etc.) that are sensitive to the disruption of particles within the system
  • Also used in conjunction with vent valves when venting a system to avoid extreme pressure differentials and high turbulence

These valves feature a vane, held open by a pair of coil springs, that pivots about an off-center axis.

Whenever the pressure differential is low enough, the vane opens.

When the roughing pump is operated, the initial flow causes the vane assembly to close—automatically throttling the pump. Also, the valves close quickly at the start of system evacuation and open automatically when a set pressure differential is reached.

Additional benefits and features

  • Reduce particulate contamination by reducing turbulence
  • Prevent substrate damage
  • Replace expensive pressure control bypass valves
  • Fast-action vane closing—12ms or better during testing**
  • Operate without electrical power
  • Replace KF centering ring for easy installation


  • * Typical pumpdown time using the soft start check valve is increased by 3X.
  • **Test times measured using a 27 CFM pump evacuating a volume of 100 liters. Results will vary based on system configuration



Lesker Soft Start Check Valves (KF flanged)


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