Vacuum pumps are predominantly used in diesel engines of passenger cars and trucks for generating vacuum in servo brake applications. With the emission norms getting stringent, there is a need for vacuum signal for EGR actuation, turbo-charger waste gate actuation and other servo applications. These multi-functional applications of vacuum pumps and the functional criticality in application like braking system demand an effective and reliable performance. In gasoline engines, the vacuum generated in the intake manifold is tapped for braking. The recent technology of gasoline direct injection compels the use of vacuum pump in gasoline engines also due to scarce vacuum in intake manifold.The performance of the vacuum pump is highly dependent on the opening and closing of the check valve sub-system, which is positioned between the vacuum reservoir and the pump at the suction side. Hence, it becomes critical to investigate and optimize the airflow through the check valve sub-system, upfront during the concept and design verification stage.Numerical tool comes in handy to investigate and optimize the flow through the check valve. In this investigation, transient conditions are identified and simulated to study the airflow and pressure drop through check valve. A check valve sub-system consists of valve body, valve, spring and retainer. Numerical studies were conducted to optimize the passage within the boundary conditions.Numerical studies helped in visualizing the flow through the check valve sub-system and in understanding the behavior of vacuum pumps. Various factors like response time, mass flow rate and vacuum chamber pressure were studied for three configurations of the sub-system. Numerical results were validated with experimental results and the difference between the performances predicted by numerical simulation and corresponding experimental values was found within 7%. Based on the obtained results, it is possible to select the optimum size of check valve sub-system for a given pump capacity.