Abstract: A load-unload device is disclosed for use in a vertical conveyor system hng means for sensing a jam condition between a downward moving conveyor tray and an article that has failed to remove from the load-unload device. The device includes linkage means for creating an over-center locked condition automatically releasable at a preset force. A spring receives the load due to a jam and develops the force necessary to unlock the linkage and allow the platform to move to a position for relieving the overload. A limit switch opens the conveyor drive motor down circuit as the platform moves. Provision is made for presetting a limited amount of platform movement without shutting off the conveyor.