This study proposes a new concept for quantifying the energy of flowing compressed air, called air power. Air power is defined as the work-producing potential of compressed air, and its definition and general equation are presented. The properties of air power are also discussed. Air power is comprised of two components, transmission power and expansion power, while air temperature and kinetic energy can generally be neglected.

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.

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In this paper, a chamber called an “Isothermal Chamber” was developed. The isothermal chamber can almost realize isothermal condition due to larger heat transfer area and heat transfer coefficient by stuffing steel wool in it. Using this chamber, a simple method to measure flow rates of ideal gases was developed. As the process during charge or discharge is almost isothermal, instantaneous flow rates charged into or discharged from the chamber can be obtained measuring only pressure in the chamber. The steady and the unsteady flow rate of air were measured by the proposed method, and the effectiveness of the method was demonstrated. [S0022-0434(00)00301-4]