Granular material unloading vehicle with pressure-relief box

An improved granular material unloading vehicle, such as a feed grain cart, comprising a wheeled chassis having a material bin mounted thereto, a substantially horizontal screw conveyor for moving the material from the bin through a discharge opening therein, a substantially vertical screw conveyor in material communication with the horizontal conveyor outside the bin for further moving the material therethrough, a power transmission arrangement for cooperatively driving the horizontal and vertical conveyors and a pressure-relief device for assisting with the start of material conveyance from the bin by relieving pressure in the forward end of the horizontal auger outside the bin and adjacent the junction with the vertical auger during the start of material transfer therebetween. This pressure-relief device includes an elongated inverted box mounted atop the horizontal auger adjacent its forward end and enclosing an internal chamber for expansion of the feed grain during initial or subsequent starts of the unloading operation. The device eliminates the problems of back charging and jamming in the horizontal conveyor and avoids the potential for resulting damage to the farm equipment without slowing down the unloading operation.