Abstract

In this paper an alternative method for obtaining the sonic conductance of pneumatic valves, C, is presented. The method uses the characteristic unloading time defined in a transitory discharge process and supposes an experimental cost lower than the ISO 6358 procedure. With this method the test rig needed is not so large and a precise measure of the variables involved in the discharge, pressure, mean temperature or specific volume, is not required either. Furthermore, the author has found experimentally that C depends on the geometric factor L/D of the chamber that impulses the mass flow rate and not only on the effective section A of the valve element. The sonic conductance obtained by the characteristic unloading time method is smaller than the obtained by the ISO 6358, and finally explains some experimental points. Firstly, the effective mass flow through some valves is significantly inferior to the one expected when considering the C ISO estimation. And secondly, it looks like if the valve would conduce a different mass flow depending on the system to which it is connected.

Keywords: sonic conductance, mass flow rate, pneumatic valves and nozzles, characteristic time