Hydraulic fluids are essentially nothing but base fluids blended with a host of chemicals, called additives, to impart or enhance desired properties and performance characteristics. Base fluids can be either from petroleum stock or synthetic fluids. Mineral hydraulic oils are derivatives from petroleum stock and are basically hydrocarbons—compounds of carbon and hydrogen. Over 95 percent of the lubricants in use today are made from petroleum stock; among all the hydraulic fluids, mineral oil is the most widely used. The reasons are:
• It is available in a wide range of viscosity, and hence users have a wide choice of selection for any application.
• Its performance can be enhanced or modified by blending with suitable additives.
• It is chemically inert and compatible with a variety of materials and other industrial lubricants.
• It can be used for lubrication of other machine elements, for example bearings and gears, thus helping in rationalization of lubricants.
• It requires a less rigorous maintenance schedule and retains its properties over a long period of time.
• It is cost-effective.