In this paper, two new methods for obtaining the sonic conductance and the critical pressure ratio of pneumatic valves are proposed. Both methods use a chamber that can approximate isothermal conditions. This was achieved by filling the chamber with metal wire, which creates a larger heat transfer area and heat transfer coefficient. The sonic conductance and the critical pressure ratio are obtained by measuring the pressure in the chamber during charging and discharging. These methods take only seconds to perform and require less energy than the ISO 6358 procedure. The major factor in the error for the pressure response during the charging of the isothermal chamber is the upstream pressure change. Nevertheless, the sonic conductance can be determined within a 3% uncertainty. In addition, the sonic conductance calculated from the pressure response during the discharging of the chamber can be determined within a 1.2% uncertainty.
In this paper, alternative methods for obtaining the sonic conductance and the critical pressure ratio are presented.The methods use the isothermal chamber that can almost realize isothermal condition due to larger heat transfer area and heat transfer coefficient by stuffing metal wire in it. Using this chamber, the sonic conductance and the critical pressure ratio are obtained by measuring only pressure in the chamber. With this method, it takes only some seconds and costs lower energy than the ISO 6358 procedure. Furthermore, the authors haveinvestigated the effect of temperature change in the isothermal chamber. In the proposed charge method, temperature change affects pneumatic characteristics measurement not so much. On the other hand, the proposed discharge method is easy to be influenced by temperature change. However, the discharge method has the merits not to dependon the dynamic characteristics of the regulator and to simplify the measurement system.
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