Experimental Methods in Valve Characteristic Assessment

Abstract: This thesis deals with experimental methods for assessing performance and characteristics of fluid power valves. Mobile applications are traditionally manually operated open-loop systems. However, there is an increasing number of applications where it is interesting to use feedback controls in an outer loop. In order to design the control systems, accurate data describing the dynamic properties of all the components in the system are necessary. The control valve is no exception.In addition to the flow gain the flow-pressure characteristics of the valve have great influence on the system properties. The relation between flow and the surrounding pressures, often described by the flow-pressure coefficient, has strong influence on the system damping and also the sensitivity to load interaction.A method to determine the dynamic flow-pressure relation and the relation between flow and input signal has been developed. The test method has the capability to determine the flow-pressure relation with respect to inlet or outlet pressure separately.Modern mobile control valves have developed into sophisticated designs incorporating several internal hydromechanical or electrohydraulic control systems, e.g. load sensing, pressure compensation and load pressure feedback. The internal feedbacks enhance the controllability but also make the valves more prone to interact in unforseen ways with the rest of the system.To reduce the need for costly full-scale tests usually used to analyse the interaction between a valve and a specific system a load simulator for testing valves has been developed. The test valve is connected to a simulated load system using a technique referred to as "hardware-in-theloop" simulation. This makes it possible to study the interaction between the test object and various systems as the simulated load system easily can be changed, thus reducing time as well as cost.Even though the work presented in this thesis has been focused on valves intended for mobile applications the presented methods are also applicable for testing other valve types, as well as components. Both of the developed test methods can easily be made fully automatic and built as compact test units housing all necessary transducers.