In this study, the specifications of the components of the vent vale were optimally determined in order to enhance the performance of the vent valve. Design objective was to minimize fuel leakage while satisfying the design constraints on the performance indices. To obtain the optimum solution based on real experiments, several design techniques available in PIAnO, a commercial PIDO tool, were used. First, an orthogonal array was used to generate training design points and then real experiments were performed to measure the experimental data at the training design points. Next, Kriging metamodels for the objective function and design constraints were generated using the experimental data. Finally, a genetic algorithm was employed to obtain the optimization results using the Kriging models. Fuel leakage of the optimized vent valve was found to be reduced by 95.8% compared to that of the initial one while satisfying all the design constraints.