T. Stanciu, A. Constantin
Thursday 11 October 2018 by Libadmin2018


The pressure regulators used in underwater breathing apparatuses determine the respiratory comfort of the diver. Our study focuses on the turbulent flow of gas through the series of valves and nozzles that are component elements of a pressure regulator. The pneumatic resistance, induced by the mechanism that controls the dependence between the air flow rate and the pressure differential created by the diver’s air intake, influences to a notable degree the breathing effort. The second stage of an underwater regulator decreases the medium pressure breathing air offered by the first stage, at 8-9 bar above the ambient pressure, to the ambient one. The air flow is critical (Mach number equals 1) in the smallest cross-section of the pneumatic circuit. The downstream valve of the second stage of an unbalanced underwater regulator is regarded as a variable section nozzle mounted in series with an orifice made in the poppet tube that conveys air to the casing of the second stage and further, to the mouth piece. Theoretical results regarding air flow rate and pressure drop in the main cross-sections of the pneumatic path are compared to the values obtained by numerical simulation and laboratory experiments on performance testing machines. Experimental results allowed us to assess the flow rate coefficients for different shapes of this orifice made in the poppet tube.

Keywords: compressible fluids, air flow rate, orifice, critical flow

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