The objective of this research was an in-depth analysis of energy losses in hydraulic systems. Energy losses were analysed on the basis of the leakage in the annular gap between the spool of hydraulic directional control valves and the hole channel. The impact of various annular gap heights during the different pressure conditions was investigated for two hydraulic fluids with different viscosities: tap water and ISO VG 46 mineral oil. The results were obtained using analytical, simulation and experimental methods. The results of leakage show good agreement between these three approaches. It was shown that grooves with an unusually larger gap (100 µm) led to less leakage in the case of the hydraulic fluid with the lower viscosity. Although the presence of a groove in combination with standard, small gaps (in classic hydraulic systems: 1 µm–5 µm) leads to greater leakage, the grooves are important to reduce the contact pressure along the sealing side of the spool, friction and wear.

A gerotor with the floating outer ring is a low speed high torque hydraulic motor. It is a special type of hydraulic motor, which is very rarely described in literature. In this study, the pressure and efficiency characteristics of...

The increasing focus on reducing the environmental impact of hydraulic applications has driven efforts to apply new surface-engineering technologies and replace classic lubricants with alternative solutions. In particular, water has gained increasing attention in recent years. However, water has very poor lubrication properties and, especially in combination with steel/steel contact, it leads to severe tribological behavior. A literature review and preliminary research showed that appropriate surface engineering regarding diamond-like carbon (DLC) coatings represents a promising solution to overcome the limitation of steel/steel contacts in water. Basic tribological ball-on-disc tests were performed. The result of the tribological investigation showed that there was very low friction and wear in the steel/DLC contact in water. This was our motivation for using DLC coating in a real hydraulic application. The DLC was deployed on the floating outer ring, so steel/DLC contacts between the floating outer ring and three other important parts were created. It was proven that the poor lubrication properties of the water were overcome with appropriate surface engineering. In such a case, the hydraulic motor operated satisfactorily when the water was applied as a working fluid.

The primary purpose of this paper is to estimate possible energy and cost savings in the optimization of mobile hydraulics. A gerotor is a low-speed, high-torque hydraulic motor, which is very rarely described in the literature and often use in mobile hydraulics. In this paper, the total efficiency of the hydraulic motor was investigated. The influence of the size of the holes in the valve plate on the total efficiency of the gerotor was analysed. The total efficiency is the most important and prominent information about the energy conversion of hydraulic components, such as hydraulic motors and pumps. The operation of a gerotor is briefly described as well as some equations for the determination of displacement and efficiency. The results show that there is a correlation between the size of holes in the valve plate and the total efficiency of the gerotor. Furthermore, a very high total efficiency was obtained with the hole size of Φ6.3 mm. In that case, the total efficiency was on average 16.1% higher in comparison to the total ef- ficiency when the hole size was Φ5.5 mm. It plays a significant role in possible reductions in energy cost. Energy analysis and cost estimation were conducted.