There is also the hydraulic fluid to consider. The pressure applied to the fluid will give the fluid the power necessary to transmit a force within the system. As the sophistication of the system increases , the work required of the fluid will also increase. The fluid transmits power while it lubricates the components which it flows through. The hydraulic fluid, as a lubricant, reduces friction in the components by producing a barrier or film which separates the surfaces that will roll or slide past each other.
Viscosity is a measure of a fluid's resistance to flow.
Viscosity of the fluid is directly related to its ability to lubricate. A high viscosity fluid generates greater film thickness between lubricated surfaces because it has a greater resistance to being squeezed out from between the lubricated surfaces. Viscosity of the fluid will change with the temperature of the fluid. Raising the temperature of the fluid will reduce its viscosity. Conversely, lowering of the temperature will increase its viscosity.