Directional valves are usually a spool type, which means, that the spool inside the valve is sliding through the bore in the valves housing. In doing so friction, wear and leakage occur. Because the housing is usually softer than the spool inside the valve, signs of wear typically begin to appear on it. The purpose of the research was to determine the optimal material pair for the spool and housing through tribological and hydraulic research, so that the valve would have the longest possible lifespan in practice. The piston is made of high-quality structural steel 42CrMo4, while the valve housings are made of C45, 42CrMo4, and free-cutting steel 11SMn30 with different bore roughness levels. In the tribological research, we conducted tests using the pin-on-disc method, while in the hydraulic research, we performed durability tests. In the tribological tests, the coefficient of friction and specific wear were measured,
while in the hydraulic tests, the internal leakage of the valves and pressures were measured. Based on the results of the measured parameters, the most suitable material pair was selected.
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