A hydraulic device is any device that uses an incompressible liquid such as oil to exert force from one point to another. Hydraulic devices use Pascal's law to multiply the exerted force, enabling them to accomplish a wide range of tasks, ranging from small assembly processes to integrated steel- and paper-mill applications.
A hydraulic device consists of a reservoir, pump, valve(s) and actuator(s). The reservoir holds a volume of hydraulic liquid and facilitates the release of air and moisture from the fluid. The pump converts mechanical energy into hydraulic energy when a transmission medium such as a lever moves the fluid inside the reservoir. The hydraulic valves start, stop and direct fluid flow, whereas the actuators convert the hydraulic energy back into multiplied mechanical energy.
For instance, an input force of 100 pounds on 10 square inches supports a 1000-pound weight if the area of the weight is 100 square inches. The reason that this is possible is Pascal's law, which states that the pressure applied to a confined fluid at any point remains undiminished throughout the fluid in all directions. Since hydraulic fluid is incompressible, it can transmit power instantaneously. According to MachineryLubrication, the three common varieties of hydraulic fluids found on the market today are petroleum-based, water-based and synthetics.