Solutia SkyDrol 5 High-Temperature Hydraulic Fluid - SAE AS1242

Phosphate ester hydraulic fluid can degrade with time and temperature via two chemical mechanisms: hydrolysis and oxidation.

Hydrolysis is a chemical decomposition of the phosphate ester base stock of the hydraulic fluid. The rate of hydrolytic decomposition of the fluid is proportional to the water content and the temperature of the fluid. Skydrol 5’s patented formulation is built on a new phosphate ester base stock, Tri-isoButyl Phosphate. Type IV fluids are built on Tri-Butyl Phosphate. Tri-isoButyl Phosphate is more resistant to hydrolysisthan Tri-butyl Phosphate.

Oxidation is a chain reaction that leads to the degradation of the hydraulic fluid. The rate of oxidation is proportional to temperature. Anti-oxidants are added to fluid formulations to minimize the contribution of oxidation to fluid degradation. Skydrol 5 contains a more robust package of anti-oxidants than any Type IV fluid. This package of anti-oxidants makes Skydrol 5 more resistant to oxidation, and therefore, Skydrol 5 can operate for longer periods of time at higher temperatures.

The useful life of Skydrol 5 is more than twice that of Type IV fluids at 275 F. At 350 F, the useful life of Skydrol 5 is approximately four times longer than Type IV fluids.

The useful life of Skydrol 5 is compared with Type IV fluids in Figures 1 and 2, for two different moisture levels, at 212°F/100°C. The useful life of the fluids is based on sealed tube experiments. It is important to note that the useful fluid life is defined at a constant exposure temperature. While the temperature in a working hydraulic system normally remains below 225°F, the temperature of the fluid may be much higher at localized hot spots. The actual improvement in fluid life of Skydrol 5 over Type IV fluids will depend on the thermal environment of each particular system.

Skydrol 5 has been designed to provide the same erosion protection characteristics at 275°F/135°C that Skydrol Type IV fluids have demonstrated at 225°F/107°C. Skydrol 5 displays outstanding erosion protection and reliable pump performance at these elevated temperatures.

Airframe manufacturers and operators are becoming more conscious of the benefits of weight saving in today’s competitive environment. Any weight that can be removed from an aircraft translates to increased payload and/or fuel savings. Skydrol 5 sets a new standard as the lowest density phosphate-ester based hydraulic fluid.

The density of Skydrol 5 is lower than the density of existing Type IV fluids. Typical weight savings per aircraft model are given in the table. The use of Skydrol 5 can translate into 5 to 120 pounds of weight savings depending on the aircraft model. This weight saving will lead directly to reduced fuel burn!