The task of the solid conveying zone is to collect the entering material and transfer it to the compression zone. Therefore, its upstream interface is the hopper and its downstream interface is the melting zone where the first melting takes place. In general the screw channel is completely filled in which the gravitation acts on the pellets and creates a movement from the barrel onto the horizontally positioned screw. The screw rotation collects and conveys the material forward. For that reason commonly known models for describing the solid conveying in single screw extruders assuming that the screw channel is always completely filled so that a plug flow occurs. At high screw speeds however, these assumptions are no longer valid. In previous investigations, simulations based on the Discrete Element Method have been carried out to analyze and describe the throughput behavior at screws speeds up to 2000 rpm. The so found model for describing the solid conveying behavior allows a variation of general screw and hopper geometry parameters but neglects the backpressure that inhibits the solid movement. For that reason, further investigations are presented in this paper, which allow an extension of the known model by considering the pressure build-up in the feeding zone. Astonishingly, at high screw speeds a low filling degree in the screw channel was observed which didn´t meet the expectations that a backpressure always leads to a fully filled channel due to a particle backlog. Afterwards the conducted simulations were validated by experimental investigations. Therefore, a test stand was designed, which allows solid conveying analysis with adjustable backpressures. The results showed a good agreement with the formulated model which now allows the calculation of solid conveying zones with consideration of the pressure build-up and filling degrees.