Hydraulic Fluids
Background & Properties
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May 2025
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Important Anti-wear Hydraulic Fluid Properties
Tractor Hydraulic Fluid (THF)
When formulated to meet OEM specifications, THFs are designed to operate in the presence of water. Good
hydraulic pump and wear protection result from a GL-4 level of gear wear protection. OEMs do not monitor
THFs and low-cost marginal base oils and incomplete additive systems can sometimes show up in low-priced
fluids. THF's viscosity grades may be too high for some hydraulic applications but are the best choice for
consistently water-contaminated systems.
Biodegradable Fluids
Biodegradability simply means a chemical breakdown of the material by living organisms in the environment.
e biodegradable portions of the fluid biodegrade to carbon dioxide and water.
e definitions in the oil industry are:
Inherently biodegradable: An oil that degrades >20% in an extended period of time. (By that definition, all oil
products are inherently biodegradable.)
Readily biodegradable: >60% of the oil is converted/biodegraded in 28 days.
N.B. No oil fluids will completely break down and return to nature within one year.
Non Toxic Fluids
Fluids which have a low level of toxicity to living organisms. White mineral oil and vegetable oil would be
common examples.
R & O Fluids
Lubricant where the only additives are antioxidants and corrosion inhibitors (most rust inhibitors). ere are
no anti-wear or EP additives present. Such a lubricant is appropriate for air compressors, non anti-wear
hydraulic and circulating systems, as well as non-EP gear oil applications.
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