Anti Wear Properties of Hydraulic Fluid

Anti Wear Properties of Hydraulic Fluid

Conventional hydraulic fluids are satisfactory for low-pressure and low-speed applications. However, hydraulic fluids for high-pressure (over 6900 kPa or 1000.5 lb/sq in) and high-speed (over 1200 rpm) applications that use vane or gear pumps must contain antiwear additives. These applications do not permit the formation of full fluid film lubrication to protect contacting surfaces--a condition known as boundary lubrication. Boundary lubrication occurs when the fluid viscosity is insufficient to prevent surface contact. Antiwear additives provide a protective film at the contact surfaces to minimize wear. At best, use of a hydraulic fluid without the proper antiwear additives will cause premature wear of the pumps and cause inadequate system pressure. Eventually the pumps will be destroyed.

Quality assurance of antiwear properties is determined through standard laboratory testing. Laboratory tests to evaluate antiwear properties of a hydraulic fluid are performed in accordance with ASTM D 2882. This test procedure is generally conducted with a variety of high-speed, high-pressure pump models manufactured by Vickers or Denison. Throughout the tests, the pumps are operated for a specified period. At the end of each period the pumps are disassembled and specified components are weighed. The weight of each component is compared to its initial weight; the difference reflects the amount of wear experienced by the pumps for the operating period. The components are also inspected for visual signs of wear and stress.