Blaise Pascal discovered the power of fluids around the year 1650. He propounded a theory that the pressure developed on a confined fluid acts equally through the fluid in all directions. The mechanical lever was the only known device till then for moving heavy masses in order to gain mechanical advantage. Pascal's discovery gave birth to the “fluid lever,” or, in today's parlance, “fluid power,” for force amplification (fig. 1—1).
As with many discoveries, Pascal's was not put into use for a long time. The first known application of Pascal's law was the hydraulically operated Bramah Press, which used water as the hydraulic fluid for power transmission — 100 years after Pascal's time . The application of fluid power since then has expanded leaps and bounds, in practically all conceivable engineering devices — from hi-tech aerospace applications to entertainment artifacts, machine tools to mobile equipment, and sugar mills to simple loading platforms.
The functions, operating conditions, and the types and ranges of fluid power machinery are so varied now that the fluids used in hydraulic systems over the years has also gone through many development stages to meet such varied performance requirements. Consequently, many types of hydraulic fluids have also emerged. Hydraulic fluid is a vital component of the hydraulic system, and it will be seen that no other component in the hydraulic system is as multifunctional as the fluid.