A check valve unit is provided for a high-speed phase change ink image producing machine between a reservoir for receiving and holding a volume of melted ink from a source and a receiving unit, which may be a printhead system. The check valve unit includes a plurality of ball elements trapped between upper and lower housings defining a like plurality of inlet and discharge passageways. The passageways are configured to optimize flow of melted ink through the unit during charging of the secondary reservoir. The check valve unit is scalable as to size and number of reservoirs for a particular application. The unit further incorporates features that simplify the manufacturing and assembly process while maintaining optimal performance.