Hydraulic fluid is the power-transmitting medium in hydraulic machinery, formulated from mineral oil, synthetic base stocks, or water-glycol mixtures. Beyond transmitting force, it must lubricate pumps and valves, dissipate heat, and seal clearances between moving parts. These fluids require specific additive packages to resist foaming, prevent rust, and shed water.
We blew a line on the excavator and dumped thirty gallons of hydraulic fluid into the dirt.
Never mix different types of hydraulic fluid. Mixing a zinc-based anti-wear fluid with an ashless fluid can cause the additives to drop out and plug the system filters.
Also heard as
- hydraulic oil
Related terms
Demulsibility
How quickly an oil sheds water and settles into clean layers after being churned with it.
R&O
Rust and oxidation inhibited: a lightly additized oil with no antiwear or EP chemistry.
ISO VG
ISO viscosity grade, the number on an industrial oil that names its kinematic viscosity in cSt at 40 C.