A new diodicity evaluation criteria, Volumetric Diodicity (Dv), is introduced to analyze the diodicity of NMP (No-Moving-Parts) valves. Recent studies about the valve system are based on the pressure diodicity, defined as the ratio between the pressure drop in forward and reverse flow. However, existing evaluation criteria do not show discrete relationships with actual data. In this paper, an inelastic collision-based analytic turbulent model was designed to approximate the tendency of diodicity by stage number and was verified both experimentally and numerically with CFD (Computational Fluid Dynamics). The new diodicity criterion can be applied in numerous fields that require NMP valves which are operated in relatively low-pressure ranges.