Improving the performance of a proportional 4/3 water-hydraulic valve by using a diamond-like-carbon coating

► Lifetime performance of real-scale 4/3 water-hydraulic valve is studied. ► We compare two types of contacts in the valve: steel/steel and DLC/steel. ► DLC coating significantly reduces the leakage of the valve compared to steel valve. ► DLC coating significantly reduces the wear of the valve compared to steel valve. ► On steel counterpart low-friction amorphous transfer film is formed.