Hydraulic fluids - Influencing factors

For a hydraulic fluid, first and foremost good thermal stability is required, followed by good lubricity, a good viscosity curve, a good compressibility factor and good resistance to oxidation. Certainly, fire resistance is a useful feature for a hydraulic fluid operating at high pressure, and particularly so in an aircraft circuit where it circulates to all points of the structure.

This article examines the influence of these properties on fluid quality.