Pressurized metered-dose inhalers (pMDIs) have been the most effective therapeutic treatment for controlling lung diseases such as asthma and COPD. The flow through a two-orifice system of pMDI is very complex and poorly understood. Previous experimental work has shown that metastability may play a significant role in determining the flow conditions inside pMDIs. In this paper, we present the findings of a homogeneous equilibrium model with those of a delayed equilibrium model (DEM) accounting for propellant metastability. These results are compared with the available experimental and numerical predictions Further, the DEM was applied with HFA propellants R134A and R227, and the results were compared with traditional propellant R12.