A nonlinear dynamic model of a Honeywell Lucifer-type EPP3 J-21-U-100-10 (now Parker P3P-R) pneumatic proportional pressure valve is formulated by modeling the valve's main internal mechatronic devices in order to simulate its dynamic behavior in the time and frequency domains, for several operating conditions and different downstream loads. Mechatronic design and functionality of this valve are carefully analyzed by considering the conditions of its internal devices for each of the three standard working configurations of a three-way proportional valve. The main physical parameters introduced in formulating the dynamic model were identified by means of an experimental investigation. Finally, the experimental and simulated diagrams in the time and frequency domains are compared in order to validate the proposed model, which can be used as a general approach for modeling any pneumatic proportional pressure valve featuring a similar mechatronic design and internal structure.