The environment management system of an aircraft requires regulated air at nearly constant temperature and pressure, despite their wide variations at the system inlet. A pressure regulation valve is an important part of that system. In response to the variation of inlet pressure, a change in the motive flow force on a spool causes a change in the steady-state opening of an orifice in the main flow path, thereby providing the pressure regulation. The change in the flow force is contributed both by the main flow and a pilot flow through a fixed orifice and a relief valve. Simple models for the pilot flow and the pressure dynamics of a pilot chamber at the head side of the spool have been developed here for capturing the spool dynamics. The transient flow through the fixed valve body and the moving spool chamber has been solved by finite-volume method with dynamic meshing. The numerical results of the pressure drop in the main flow path for the fully open spool valve have shown good agreement with the corresponding experimental results with the pilot-line flow put off by the closed relief valve. Detailed analysis of the transient main flow leading to useful design conclusions has been provided in terms of different contour plots. For a given specification of the spool valve, a parametric study has provided the appropriate length of the pilot chamber, the stiffness of the spring in the relief valve, and the size of the fixed orifice in the pilot line.