As part of the final thesis, we experimentally analysed the behaviour of directional control valves in relation to their internal leakage, when the input parameters were changed. The main objective of the final thesis was to list the causes of changes in the operation of the directional control valves, whose bodies are manufactured by additive three-dimensional printing. The focus was on a changed internal leakage of unknown origin. The analyses were based on changing input parameters, which are related to the type of fluid, the temperature at which the system is operated, and the pressure in the system, as well as listing the effects caused by different combinations of given parameters on the operation and leakage of the system. For comparison, a standard valve, mass-produced by the casting process, was tested in parallel. Three different fluids were used in the laboratory tests, namely water, mineral hydraulic oil ISO VG 46 and glycol. Since it is difficult to keep up temperature of the test fluids stable, the values of 50 °C and 70 °C were used as input data. The tests were performed at three different pressure levels: 100 bar, 200 bar, and 300 bar. Since the geometry of the spool in the valve differs from the geometric shape of the cylinder, its torsion was considered as the last parameter.
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