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Hydraulic Oil

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Hydraulic oils, also called hydraulic fluids, are the medium by which power is transmitted in hydraulic system. Hydraulic fluids are also responsible for lubrication, heat transfer and contamination control. Common hydraulic fluids are petroleum-based or mineral-based fluids ,water-based fluids , synthetic fluids are used. Examples of equipment that might use hydraulic fluids include excavators, brakes, power steering systems, transmissions, backhoes, garbage trucks, aircraft flight control systems and industrial machinery.

Pascal's Law: It states that pressure exerted anywhere in a confined incompressible fluid is transmitted equally in all directions throughout the fluid such that the pressure ratio (initial difference) remains the same.

Pascal constructed the first known hydraulic device, which consisted of two sealed containers connected by a tube. The pistons inside the cylinders seal against the walls of each cylinder and prevent the liquid from leaking out of the cylinder and prevent air from entering into the cylinder. When the piston in the first cylinder has a force applied to it, the pressure moves everywhere within the system. The force is transmitted through the connecting tube to the second cylinder. The pressurized fluid in the second cylinder exerts force on the bottom of the second piston, moving it upward and lifting the load on the top of it. By using this device, Pascal found he could increase the force available to do work, just as could be done with levers or gears.


One of the most important examples is the hydraulic brake system to stop moving vehicles.


  The hydraulic brake system consists of a master cylinder joined by tubes to four smaller cylinders, one for each wheel of the car. They are called brake cylinder .All cylinders are provided with oil tight pistons.

A forward push on the brake pedal causes a force on the piston in the master cylinder and a consequent pressure on the brake oil. These undiminished transmitted pressure forces the piston in each brake cylinder to act on the brake shoe attached to a caliper or against a rotor in the case of disk brake. The resulting friction stops the car.

A simple hydraulic system consists of hydraulic fluid, pistons or rams, cylinders, accumulator or oil reservoir, a complete working mechanism, and safety devices. These systems are capable of remotely controlling a wide variety of equipment by transmitting force, carried by the hydraulic fluid, in a confined medium.

Fluid Properties
Viscosity, viscosity index, oxidation stability and wear resistance are very important characteristics of a hydraulic fluid. These characteristics will determine how your fluid operates within your system. Fluid property testing is done in accordance with either American Society of Testing and Materials (ASTM) or other recognized standards organizations.


1. Viscosity (ASTM D445-97) is the measure of a fluid’s resistance to flow and shear. A fluid of higher viscosity will flow with higher resistance compared to a fluid with a low viscosity. Excessively high viscosity can contribute to high fluid temperature and greater energy consumption. Viscosity that is too high or too low can damage a system, and consequently, is the key factor when considering a hydraulic fluid.

2. Viscosity Index (ASTM D2270) is how the viscosity of a fluid changes with a change in temperature. A high VI fluid will maintain its viscosity over a broader temperature range than a low VI fluid of the same weight. High VI fluids are used where temperature extremes are expected. This is particularly important for hydraulic systems that operate outdoors.

3. Oxidation Stability (ASTM D2272 and others) is the fluid’s resistance to heat-induced degradation caused by a chemical reaction with oxygen. Oxidation greatly reduces the life of a fluid, leaving by-products such as sludge and varnish. Varnish interferes with valve functioning and can restrict flow passageways.

4. Wear Resistance (ASTM D2266 and others) is the lubricant’s ability to reduce the wear rate in frictional boundary contacts. This is achieved when the fluid forms a protective film on metal surfaces to prevent abrasion, scuffing and contact fatigue on component surfaces.







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