Issue link: http://read.dmtmag.com/i/859318
Hydraulic Fluids Background & Properties castrol.com/GPS 800 255 4417 May 2025 GPS Important Anti-wear Hydraulic Fluid Properties Viscosity Index Viscosity Index, or VI, is one of the single most important performance indicators in both a base stock and finished hydraulic fluid. Viscosity is a measure of a fluid's resistance to flow. Flow characteristics and temperature are related: oil thins at higher temperatures, making it flow more freely; oil thickens at lower temperatures, inhibiting flow. Viscosity Index is a quick way to tell whether an oil can withstand extreme high and low temperatures. VI is a measure of change in an oil's viscosity relative to a change in temperature. Oils with higher VIs experience less change in viscosity due to temperature. Higher VI oils guard against wear at high temperatures and maintain pumpability at lower temperatures. is offers customers a more reliable hydraulic fluid during all temperature ranges. Base oils that exhibit natural VIs over 95 experience less change in flow characteristics as the temperature fluctuates. In a hydraulic system, where pressure and power are partly reliant on the hydraulic fluid's viscosity, oil that is too thin or too thick will ultimately shorten component life. Saturation Levels A base oil's saturation level can also impact finished product performance. When a base fluid is highly saturated, there are less chemical opportunities for oxygen to bond with hydrocarbon molecules—a process that results in oxidation or oil breakdown. Refining techniques, such as hydrocracking and hydrotreatment, can boost the base stock's saturation levels by forcing hydrogen through the oil, saturating oil molecules with hydrogen and eliminating the oxygen molecule's ability to bond with those molecules. In essence, the base oil is now more oxidation resistant. In addition, hydrotreated base oils have a longer working life and can endure higher sump temperatures than non-treated stocks. Key Base Hydraulic Oil Stock Property Performance Criteria Viscosity Index High Temp Viscosity Control Viscosity Index and Pour Point Low Temperature Fluidity Volatility Oil Consumption Control Amount of Saturates Oxidation Stability, Seal Swell and Additive Compatibility A note on base stocks: Hydrocracked Group II base stocks provide higher VIs and higher saturation levels than Group I or napthenetic base stocks. Base Oil Types Mineral Group I and II Group I base oils have VIs of 80 to 120 and were the original, traditional hydraulic fluids base stock. Group I base oils have more sulfur and less saturates than Group II, III or IV fluids. e performance of finished lubricants blended with Group I base oils is largely dependent upon the quality of the additive package. Group II base oils are known for their excellent deposit control and high level of saturates, which makes them more oxidation resistant. ey typically have VIs of 105 up to 120 and rely heavily on additives to enhance finished lubricant characteristics. Different refining techniques work to remove unwanted characteristics and improve upon desired ones, like viscosity index and oxidation control. Most of Castrol's hydraulic fluids are blended with Group II base oils and a premium-performing additive package. C10 ecastrof