The centerpieces of modern reciprocating compressor valves are high-temperature thermoplastic sealing elements, called valve plates. These injection-molded parts perform under extreme conditions and high loads. Short carbon fiber reinforced PPS shows an excellent performance in enduring these high requirements. To raise the valve life-time, one approach is to improve the mechanical properties of the valve plate material by an optimization of the injection-molding process. High shear rates in the plastification and injecting process shorten the fibers and leads to a low average fiber-length and furthermore to lower mechanical properties. The object of this contribution is to reveal the exact influence of the processing on the fiber-length distribution and the connections to the mechanical properties of the finished part. This paper investigates the impact of the injection-molding parameters dosing rate, back pressure and injection rate on the fiber-length, by means of a full factorial experimental design. The required samples for the fiber analysis and the tension tests were milled out of injection-molded valve plates. Since carbon fibers cannot endure the high temperatures of a pyrolysis, chemical exposure was chosen as fiber separation method. Chemical exposure destroys the molecular chains of the matrix polymer and reveals the more inert carbon fibers. Due to the high chemical resistance of PPS only a pressure exposure with nitric acid under high temperature yielded an acceptable separation result. The exposure degraded the polymer matrix to hardly visible rest particles. The carbon fibers remained unharmed and showed a strong contrast in reflected-light microscopy. Several scaled microscopy images were taken from each sample and analyzed by means of a self-written image processing program to gain the fiber-length distribution. Additional tensile tests showed the macroscopic effects of the different fiber-length distributions.