Static and dynamic properties of selected hydraulic pressure reducing

A growing demand from the users of machines and hydraulic systems has created the necessity to increase the speeds, accelerations and loads of hydraulic drives. This often results in hydraulic drives working constantly in a transition state. At the same time, the area of dynamic properties of most hydraulic elements is rather unknown for most users of power hydraulics. This paper presents the results of the preliminary research on static and dynamic properties of pressure reducing valves, both with conventional and proportional control. The research focused mainly on the comparison of dynamic properties of tested elements. By dynamic properties, the authors mean pressure settling time-and its overshoot, excited by step change of the flow rate through valves. It is worth noticing that the manufacturers of conventionally controlled hydraulic valves do not include any parameters describing the dynamic features of their products. Because of the insufficient information, the constructors of hydraulic drives are unable to predict the behaviour of hydraulic drives equipped with conventional valves during transition states. The preliminary research showed that the momentary value of pressure can range widely for the pressure reducing valves. This can significantly influence on operation of a drive system. The authors propose to create procedures or norms to test the dynamic features of hydraulic valves excited by a hydraulic value (eg. step change in intensity of flow or pressure). Similar procedures were introduced in testing the proportional valves as well as servovalves, with the electric signal being the unit step function.