Determination of flow-rate characteristics for pneumatic components using a quasi-isothermal tank with temperature compensation

A measurement method is proposed to compensate temperature change for the isothermal discharge method, which determines flow-rate characteristics of pneumatic components by measuring the pressure response in a tank when air is discharged. The tank was stuffed with isothermal materials, such as a thin copper wire, to keep the temperature change small. However, the isothermal performance worsened when less material and a smaller tank were used to reduce the test device cost. This state is called quasi-isothermal. A compensation term for the temperature change in an exponential expression is proposed as a component of the flow-rate equation based on the mathematical model for the air discharge process for a quasi-isothermal tank. The compensated flow rate was found to be in good agreement with that measured by the ISO6358 Exhaust-to-atmosphere method. There were very small errors between the flow-rate characteristics of the sonic conductance C and the critical pressure ratio b as calculated by the proposed equation and the results measured by the ISO6358 method.