Proportional and servo valves are used to control the velocity, or force of an actuator. In some cases, two or more parameters have to be controlled. For example, as a cylinder is extended, its velocity might be controlled. At the end of the cylinder's stroke, the servo system may be used to either position the cylinder or to control the exerted force on the
work piece. In present study the dynamic performance of an electrohydraulic system, containing a proportional directional valve, has been investigated theoretically and verified experimentally. The electro-hydraulic system, under investigation, contains an electrohydraulic proportional valve which is used to control a hydraulic cylinder velocity under constant load. The electrohydraulic system consists of a hydraulic tank, a gear pump; a relief valve; a proportional directional valve; a hydraulic cylinder with vertical load; and connecting hoses. Experimental works have been carried out to measure the pump-relief valve characteristics and the pressure losses in the connecting hoses. These measured data have been curve fitted to simulate the characteristic of the pump-relief valve and the connecting hoses. A verified theoretical model of the directional proportional valve, which was previously presented and published in [Menshawy, T.M., “Investigation of Dynamic Behavior of an Electro-hydraulic Proportional System", M.Sc. Thesis, Military Technical College, Cairo, Egypt, 2006.], has been used here. The simulation model of the hydraulic cylinder with vertical load has been carried out. All these models have been introduced within the MATLAB-SIMULINK environment in order to obtain the theoretical simulation program of the electrohydraulic system operation. The model of the electrohydraulic proportional system has been validated experimentally and has been used to investigate the performance of the system when works under different operating conditions.