Modeling leakage gaps in Computational Fluid Dynamics (CFD) of pumps is critical in that parasitic leakage flow can severely degrade the performance and in some cases even lead to cavitation damage. Due to their complexity, leakage gaps used to be omitted from CFD models and instead attempts were made to account for them via estimates in post processing. With recent improvements in CFD capabilities, these gaps can now be rigorously included in the model as an implicit part of the simulation. Including gaps as an integral part of the model enables direct prediction of the leakage, pressures, loads, torques, and cavitation in these volumes.