Digital Hydraulics: A Theoretical Study Comparing Hydraulic Power Units

Recent research has been used to identify efficiency improvements that may be obtained by utilizing on-off hydraulic valves in the place of traditional hydraulic valves. These efficiency improvements reduce throttling losses in the valve by using wide-open valve positions that are intermittently turned on and off. While this efficiency idea has emerged with great interest among some, there are still those who remain doubtful about the efficiency improvements that have been claimed and anecdotal concerns continue to be voiced at conferences and in hallway discussions within industry. This paper is being written to address the subject from a theoretical perspective. In the analysis of this paper, the efficiency equations for an on-off valve will be derived and compared to the efficiencies of valves that are employed in pressure relief systems, pressure compensating systems, and load sensing systems. In conclusion, it is shown that valves operating in load sensing systems are always the most efficient valves, while digital valves are often the next most efficient design except during low flow conditions when the valve in a pressure compensating system may occasionally be more efficient than the digital valve. It is shown in this research that valves used in pressure relief systems are always the most inefficient design.