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Hydraulic systems are widely used in working actions of mobile machines. They offer good power to weight ratio, robustness and relatively good controllability. However, there has been growing interest on the energy efficiency of such machines during recent years. Load sensing proportional valve control is a typical solution for multi-actuator systems leaving a significant margin for improvement of energy efficiency. Digital hydraulic valve system enables independent metering and reduces losses significantly without a need of complete redesign of the hydraulic system of such machine. Digital hydraulic valve system consists of parallel connected on/off-valves and offers deterministic operation which is crucial for successful implementation of independent metering. Four different digital hydraulic valve control approaches are analyzed in the paper: four-edge-control, four-edge control with pressurized tank line, five-edge-control and six-edge-controlled three-chamber-cylinder.

Filtration in water hydraulic system may be very problematic, due to physical and biological contamination. This contamination may cause quick increase in pressure difference over the filter element, and aim of this research was to test different kinds of filters and determine the effects of microbial growth on filtration in a water hydraulic system. In this paper the results of these experiments are presented, and it is shown that the most of the micro-organisms of the water hydraulic system after experiments was on the filters.

Measuring water quality and preventing drawbacks caused by deteriorated water quality in tap water fluid power systems is a unique problem. Tap water is a suitable environment for waterborne microorganisms. It also contains dissolved and undissolved organic and inorganic matter. Wear particles in the tap water fluid power systems are a separate problem, however closely linked to problems above mentioned. Contamination and the quality of the pressure medium in the system is a function of local characteristics of tap water, operating parameters, system and component design and contamination introduced to the system. To study effects of water quality on tap water fluid power systems, and to evaluate methods for measuring water quality and particle counting, a pilot scale hydraulic system was constructed. The pilot scale system emulates typical operation of a commercial tap water fluid power system.