text: how to design and build a hydraulic device that uses the properties of fluids?   ummm what exactly are you asking, any hydraulic device uses fluids. the prefix "hydro" (or hydr before a vowel) means water or fluid. what particular properties are you asking about?  is this a school project or for a science fair? check google, but basically they all work on a cylinder. for example a log splitter. http://science.howstuffworks.com/hydraulic2.htm