Particular care was devoted to the modelling of the single EHPV valve ([19]), since the evaluation of energy dissipation in the system may depend on both the steady-state and dynamic characteristics of the metering valves. The distinguishing features of these valves include an internal pressure compensation mechanism that helps considerably to reducing the initial input current required to open the valve. The valve has a three-degrees-of- freedom internal mechanical system with state constraints. The relative displacements of the mechanical components establish the flow rate through the valve. The relationship between the valve flow rate Q, pressure difference across the valve p and the valve flow conductance Kv is defined in the following equation: