This work presents a study of the applicability of optimal control theory to the design of a pressure regulator for an axial piston pump and single-stage electrohydraulic valve combination; in addition, a two-stage electrohydraulic valve was used in combination with the pump. Modeling has been accomplished for these valve systems and optimal control laws have been formulated;In the single-stage servovalve model, the time response curves due to a step input in flow rate and in current input to the servovalue have been obtained for the open loop and for the optimal control system. Comparison of the results has been made with previous work in which the supply valve to the swashplate actuators was not modeled. It is shown that controlled system modeling of the servovalve improves significantly system performance in terms of response frequency and pressure peaks;In the two-stage servovalve model, it is found that the open loop system of the model is unstable. The frequency response of the optimal controller is slower than that when a single-stage value is used, and the peak pressures are increased by a factor of 8. It appears therefore, that the performance of the single-stage valve, in terms of pressure peaks and frequency, is superior to that of a two-stage valve.