Measurement of flow rate characteristics of pneumatic components based on the dynamic regularity of polytropic exponents

To improve the measurement precision of flow rate characteristics of pneumatic components, a new measurement method is proposed, which is based on the dynamic regularity of instantaneous polytropic exponents during discharge. The dynamic regularity of polytropic exponents is obtained by the stop method, and it can be concluded as two change stages based on pressure time constant. According to piecewise polynomial fitting curves of instantaneous polytropic exponents, a new algorithm for the identification of flow rate characteristics is proposed. This method can accurately measure some components with a large sonic conductance and a small critical pressure ratio. Four pneumatic components are measured to compare the identification precision of those different methods. The results of comparison show that the new polytropic exponent method and its new algorithm have the higher precision than other alternative methods for the ISO6358 method. The identification errors of sonic conductance of the new method are less than 3%, and the identification errors of critical pressure ratio of the new algorithm are less than 15%.

The dynamic regularity of polytropic exponents during discharge obtained by the stop method can be concluded as choked stage and sonic stage. The temperature drops during discharge can be compensated by the gradient of polytropic exponent fitting curves. Even though the pressure drop in choked stage may exceed 300 kPa per second, the polytropic exponent method can still accurately measure some pneumatic components with a large sonic conductance and small critical pressure ratio. Figure optionsDownload as PowerPoint slideHighlights
► The instantaneous polytropic exponents change mainly in the choked stage.
► The gradient of polytropic exponents and their fitting curves can compensate the measurement error.
► The polytropic exponent method can accurately measure the pneumatic components with a large sonic conductance and a small critical pressure ratio.