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Auto-Off Safety Vent Valves (KF Flanged)

Our automatic foreline shut-off valve is a safety valve that protects the vacuum system upon power failure by isolating the vacuum system and venting the mechanical pump.


  • Eliminate time consuming and costly cleanup of dirty vacuum lines, caused by oil backstreaming from the pump
  • Small orifice in the shut-off valves vents the mechanical pump to atmospheric pressure for easy restart when power resumes
  • Even when the mechanical pump is equipped with an anti-suckback valve, these valves are recommended because the pump’s integral valve will not vent the pump
  • Available in a variety of ISO-KF flange sizes, solenoid voltages, and frequencies

How it all works

The automatic foreline shut-off valves (anti suck-back vent valves) are connected in parallel with the mechanical pump’s electrical supply, either at its source or at the pump’s switch. When the electrical power is on, the solenoid valve is held closed, enabling the pump to keep both the shut-off valve’s body and the vacuum system evacuated. Interruption of electrical power to the mechanical pump causes the solenoid valve to open, admitting air into the shut-off valve, causing it to close. The pressure differential between the outside atmosphere and the vacuum system provides the necessary force to maintain the valve in its closed position without the aid of electrical or pneumatic power. With the vacuum system isolated, a series of small orifices admits air into the inlet port of the mechanical pump until it has risen to atmospheric pressure. When the power comes back on, the solenoid closes the pump. The mechanical pump is then restarted, and evacuates the area above the piston until the pressure is lowered to approximately that of the vacuum system. The automatic foreline shut-off valve then reopens, enabling the vacuum system to be pumped at the full speed of the mechanical pump.

Additional features and benefits

  • Protects vacuum system from oil backstreaming in the event of power failure (to the pump)
  • Enables quick system restarts
  • Operates up to 100,000 cycles
  • No external pressurized gas source required for actuation
  • Available in a variety of sizes for use with the most common mechanical pumps

Specifications Table

Manufacturer KJLC
Rates Leak Rate Body
1.010 x 10-9 mbar*L/s
7.620 x 10-10 Torr*L/s
Leak Rate Seal
1.010 x 10-9 mbar*L/s
7.620 x 10-10 Torr*L/s
Temperature Body Temp
100 ºC
212 ºF

Solenoid Temp
55.0 ºC
131 ºF

Valve Body
6061-T6 Aluminum
Valve Seal
2024 Aluminum
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Flange Selection Guide
With a variety of flanges to choose from, the Flange Selection Guide is designed to help you find one to meet your vacuum requirements. Shop Now!
Can't find the flange you need or want a custom configuration? Please call us at +1 800 245 1656 or email with your inquiry.
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