Automatic pressure/flow device

摘要

A device for the determination of the gas permeability of a material such as paper includes a holder 1 for holding a sample across a gas flow passage of predetermined cross section and a pump 2 for drawing air through the passageway via one or more constant flow device C1-C6 arranged in parallel. Each constant flow device has a closable control valve V1-V6 respectively. A first pressure transducer measures the pressure drop across the sample and a second pressure transducer, in cooperation with a lamina flow element measures the rate of air flow through the sample. A by-pass by-passes selectively three of the control valves of the constant flow devices. The by-pass has valves B1-B3 arranged in parallel and operable to close the by-pass to gas flow therethrough to the respective constant flow devices C1-C6. The by-pass also includes an atmospheric bleed 11 and a valve B4 closable to stop the flow of air into the by-pass.