A fifth wheel hitch may include a skid plate having a plurality of recesses, and a skid plate cover secured to the skid plate. In the outer andor inner platform there are core outlet openings which arise from the use of a casting core and which connect the cooling passage to the outside space and are sealed off by means of a sealing element. Each fluid pressure line that is in fluid communication with the purging subsystem being selectively purged by the purging subsystem when pressure monitoring subsystem determines the respective pressure line has become obstructed. When the tuning assembly axially \u201cexpands\u201d, it pushes increasingly \u201cupward\u201d against the drumhead, variably increasing its tension and the musical pitch of the drum. The proximal blocking signal is selected to at least partially block nerve impulses at the proximal blocking site. Whilst changing between performance levels, the further circuits are capable of supporting intermediate levels of operation and the processor exploits these by operating at those intermediate levels pending the final target level being reached.