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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.
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.
Lesker Auto-Off Safety Vent Valves (KF flanged)