There are three parts to the NEC fast acting valve system; the spring drive all-metal valve, coaxial pressure sensor and the trigger circuit. The following describes the fast acting valve only.
The fast acting valve (Model VS2F) is identical in construction and sealing principle to the VS2P (Pneumatic Straight Through Vacuum Valve) and VS2M (Manual Straight Through Vacuum Valve) straight through valves with the addition of a unique spring closure to actuate the toggle mechanism.
When a signal is received from the pressure sensor due to a pressure rise, a special solenoid releases the trigger, and the spring drive actuates the toggle mechanism for reliable closures in less than 35 milliseconds after the trigger signal is received.
In factory tests, 50 successful fast closings were made on the same aluminum seat without replacement. If the valve fails to seal, a simple in-line adjustment provides another series of successful closures without changing seals or breaking vacuum.
This valve can be operated in either the manual or fast acting mode. Resetting is done manually with a cocking handle supplied with the valve.
As with other NEC straight through valves, all flanges compatible with nominal 2” stainless steel tubing are available. Special extensions have been provided to accommodate 2.75” O.D. flanges.
Although designed for UHV systems, applications permitting o-ring seals can take advantage of an optional seal disk incorporating a Viton o-ring. This would be particularly valuable on systems that experience frequent vacuum failures.
The NEC coaxial pressure sensor and trigger controller are used with the fast acting valve and sensor trigger controller for reliable protection against catastrophic vacuum failure.
The NEC coaxial pressure sensor, which consists of a fine wire along the axis of a small grounded cylinder, detects a pressure rise, to a selectable level of 10-4 to10-2 Torr. The wire stays at a few kilovolts potential. As the pressure rises above the selected limit, a discharge occurs and a large current flows between the wire and the cylinder. This signal allows actuation of the trigger solenoid at the fast acting valve.
All materials in the coaxial pressure sensor are ultra-high vacuum compatible. There are no organic compounds in the vacuum volume.
This circuit uses the current signal from the coaxial sensor to discharge a capacitor into the valve trigger solenoid. This in turn releases the trigger plate that normally holds the handle of the fast acting valve in the open (cocked) position. Closure time is less than 35 milliseconds after receiving the trigger signal.
The sensor controller panel indicates the status of the valve, fired or disabled, and power to the unit. There is a switch on the front panel that allows the manual firing and able or disable of firing mechanism. There is also a trigger pressure sensitivity adjustment.
The complete system – consisting of the fast acting valve, coaxial pressure sensor and the trigger controller – provides reliable protection against damage due to catastrophic vacuum failure.
If multiple valves need to be triggered simultaneously, an additional controller (valve trigger controller) can be added to the CPS system to trigger a secondary valve when the CPS system triggers the primary valve.
NEC designed the coaxial pressure sensor to interface with the NEC sensor trigger controller, Model PS4, to actuate the NEC fast acting valve.
Triggering Pressure: |
Adjustable from 1 x 10-4 Torr to 1 x 10-2 Torr (measured for a gradual pressure rise) |
Sensor Mount: |
Standard NEC 3.5” O.D. NEC flange.(other flanges available on request) |
Sensor Controller: |
Input: 115V, 50-60Hz, 0.5A |
| Output: 4.3kV peak, 200mA |
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