The use of a silicon carbide porous plug for the control of gas flow into a vacuum system down to 1 l torr sec-1

Abstract

Results are presented on the suitability of a porous plug as the basic element for the control and measurement of gas flow in a vacuum system. A plug of silicon carbide is shown to have a very low gas conductance, of the order of 1 μl sec-1. Because the plug is, in effect, a large number of very fine interconnected capillary tubes, the flow obeys the basic Knudsen laws of molecular flow, i.e. flow is proportional to pressure difference up to at least 100 torr and also to the square root of the gas molecular weight. The stability of calibration and the agreement with theory is reported to be within ±1% for the inert gases, that is within the limits of measurements of these experiments. It is estimated that this accuracy can be maintained for flow rates down to 1 or even 0.01 μl torr sec-1.