Different types of pilot stages for a water hydraulic control valve

Large hydraulic valves usually have several stages. Typical solution is a two-stage valve with a pilot stage and a main stage. Multi-stage valves are usually required when the the output power of valves increases or the power level of control signals is low. In oil hydraulics there are well-known solution of different valve-stages in the water hydraulics there are no generally accepted solutions. Reasons are partly the newness of technology and partly the nature of water. The pilot stage can be controlled with analog or digital signals. Usually the analog signals are used, but in the water hydraulics, the digital signals can also be considered. The effects of different valve configurations of fast on/off-valves in the digital pilot stage are discussed in details by comparing performance and lifetime. The digital and the analog pilot stages are compared with each other. Analog pilot stages like nozzle-flapper, jet pipe and deflector jet types are introduced. A valve prototype with nozzle-flapper hydraulic pilot stage is tested and results are shown.