The key role of hydraulic oil in a hydraulic system is to transfer power from one end of that system to another end through and the various hydraulic components.
When an external force is applied to the non-compressible hydraulic fluid – usually from a piston within a cylinder – the oil is pushed through the hydraulic system and ultimately produces a force on another part of the system. This results in a movement or action.
Usually applying force to material results in compression, so you may be wondering whether hydraulic oil is compressible or not, but a key property of hydraulic fluids is that they must be non-compressible.
‘Non-compressible’ means that the fluid cannot be compressed. Liquids are compressible to some degree, but it is incredibly negligible and not considered for our guide. In contrast, gases are compressible, and so are not used in hydraulics.