Numerical investigations of the flow and pressure fields within a homogenizer valve have been conducted using the computational fluid dynamics code, PHOENICS 2.1. Results are obtained for two valve seat designs over a range of valve gaps. The dependence of valve gap on operating pressure is measured experimentally and compares well with numerical predictions. A simple expression that uses the numerical results and allows ready calculation of pressure gradient from homogenizer operating and design conditions is presented. Pressure gradient is shown to be a better independent variable for correlating cell disruption than operating pressure over a wide range of operating and design parameters.