A wide variety of valve designs – e.g. cartridge, CETOP, sandwich, subplate valves – and general operating principles – e.g. poppet valves, spool valves or rotary valves – are used for hydraulic control tasks. Valve types are directional valves (2/2-way; 4/3-way; 3/2-way…), pressure valves – e.g. pressure relief valves, pressure reducing valves -, flow valves – e.g. 2-way flow regulators or 3-way flow regulators and special safety valves – e.g. lowering brake holding valves or unlockable check valves.