| abstract |
The present invention is a method for operating a hydraulic system at pressures of about 4000 psi or higher, preferably about 5000 psi or higher by using as the lubricant a phosphate ester hydraulic oil comprising a fire resistant phosphate esters base stock, a viscosity index improver, an anti erosion agent, an acid scavenger. The fluid used in the present method can also contain rust inhibitors and/or antioxidants. |