This document discusses the working principles of hydraulic lifts and presses. It explains that hydraulic lifts use high-pressure liquid to lift passengers or goods between floors in multi-story buildings. Hydraulic presses also use high fluid pressure to lift heavy weights using a much smaller applied force, based on Pascal's law that pressure in a fluid is transmitted equally in all directions. The document then provides details on the components and operating mechanisms of both hydraulic lifts and presses.