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A continuous-purge pulsed valve has been designed to introduce supersonic jet samples into a vacuum chamber. The new valve design separates the heated sampling and transfer lines from the solenoid coils with a long metal valve stem, which is kept cool with annular cooling fins. The valve is heated using electrical heating elements wrapped around the valve stem. A precision-machined stainless steel plunger maintains a metal-to-metal seal at the valve orifice, which is broken when the induced magnetic field from the solenoid pulls the plunger upward. Stable gas pulse widths were obtained down to 200 μs, which compares favorably with the 165 μs value for the commercial unit which uses a small Teflon poppet instead of the metal plunger.
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Şenkan et al. (1997) studied this question.
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