Hydraulic Fluid

What kinds of fluids are used in hydraulic systems? Depending on the application the system is being used for; water, vegetable oil, and (tractor) petroleum oil are used for hydraulic fluids. Water and vegetable oil is used for applications with fire or food safety hazards. Tractor fluid is used in most heavy equipment applications. Petroleum based hydraulic fuels have different additives giving them different viscosities at specific operating temperatures. The correct fluid not only ensures proper performance of the machinery, but also extends its lifespan. Some fluids contain detergents that can emulsify water and cause contaminants to float to the top of the fluid tanks. This means contaminates must be filtered out of the system. The emulsification of water also causes the oil to age more rapidly. Antiwear is another additive that can aid in lubrication. This additive is known as ZDDP, zinc dialkyl dithiophosphate. This helps to lubricate high pressure/performance systems containing piston pumps and motors.



Component Type Minimum Permissible Viscosity (cSt) Minimum Optimum Viscosity (cSt)
Vane 25 25
External Gear 10 25
Internal Gear 20 25
Radial Piston 18 30
Axial Piston 10 16