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A high vacuum needle valve may be used as an adjustable leak for regulating the flow rate of gas samples to a mass spectrometer, when the valve is equipped with a wedge and lever system providing very sensitive control of the needle position. Flow through the leak is molecular at spectrometer pressures, but mass flow may be secured by inserting a capillary tube between the sample and the leak. The leak may be closed completely, thereby simplifying the design of the sample inlet system.
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Babelay et al. (1953) studied this question.
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