Hydraulic System Component Storage with Military Hydraulic Fluids

In the military aerospace community, most hydraulic fluid pumps and components are currently being stored in rust inhibited fluids containing barium dinonylnaphthalene sulfonate (BSN). Fluids containing barium are hazardous waste after use, with expensive disposal, and have caused operational problems in aircraft hydraulic systems including helicopters and fighter aircraft. In this program, bearings and pistons were stored in jars containing both operational hydraulic fluids (MIL-PRF-83282, MIL-PRF-87257, and MIL-PRF-5606) and rust-inhibited hydraulic fluids containing BSN (MIL-PRF-46170 and MIL-PRF-6083). In addition, hydraulic pumps were filled with MIL-PRF-83282, MIL-PRF-87257, and MIL-PRF-46170. Hydraulic pumps were not filled with MIL-PRF-5606 or MIL-PRF-6083 because these hydraulic fluids are being phased out of military aerospace applications as operational and storage fluids, respectively. Jars, containing bearings and pistons, as well as hydraulic pumps, were stored for up to three years in a laboratory environment to determine if operational fluids would protect them from rusting during storage. After each year, the bearings, pistons, and pumps were inspected for corrosion. At the end of three years of storage, pumps were endurance tested using fresh operational fluid, MIL-PRF-83282. The bearings, pistons, and pumps showed no rusting for the duration of storage with either operational or storage fluids. The pumps stored with the operational fluids, MIL-PRF-83282 and MIL-PRF-87257, were in better condition than the pump stored with the rust-inhibited fluid. The operational hydraulic fluids, MIL-PRF-83282 and MIL-PRF-87257, provided excellent protection against rusting during storage.

Manuscript contributed February 1, 2005

Review led by Paul Bessette

KEY WORDS:

• Hydraulic Fluid Pumps
• Aircraft Hydraulic Systems
• Operational Fluid

ACKNOWLEDGMENTS

The authors thank Charles Tobin ¹ and Timothy Reid ¹ for conducting laboratory fluid evaluations and Gregory Palm ² for assisting with pump testing and taking photographs.

Notes

Manuscript contributed February 1, 2005

Review led by Paul Bessette

¹Hydrogenated polyalphaolefin with ∼33% ester and other smaller amounts of performance improving additives.

*= Parts soaked in fluid and drained for 10 seconds.

* = Measured water value determined by ASTM D 6304.

* = Measured water concentration determined by ASTM D 6304.

** = Water content was only measured initially and in year 3 for the bearing and piston jars.

*** = Had darkened bands on race and at the bearing contact surface areas, but no corrosion.

1. University of Dayton Research Institute, Dayton, OH.

2. Southwestern Ohio Council for Higher Education, Dayton, OH.