A container pick and return system is provided having a two-tiered flow rail conveyor system that includes an inclined upper set of feed flow rails forming an input conveyor assembly and a lower set of inclined return flow rails forming an exit conveyor upon which a unit load may roll. The first unit may include a first member configured to be placed over a door opening on a fist side of a wall and a second member which can be positioned across the opening and against a second side of the wall. The structure is protected against contamination, package leaks, and changes to the piezoelectric material due to external effects while still providing inertial resistance.