Method for lubricating high pressure hydraulic system using phosphate ester hydraulic fluid

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.

What is claimed is:  
     
         1 . A method for operating and lubricating hydraulic systems at pressure of about 4000 psi by employing as a hydraulic fluid a phosphate ester functional fluid comprising a major amount of fire resistant phosphate ester base stock and a minor effective amount of additives comprising one or more anti erosion agent(s), one or more acid scavenger(s) and one or more viscosity index improver(s).  
     
     
         2 . The method of  claim 1  wherein the hydraulic system is operating at a pressure of about 5000 psi or higher.  
     
     
         3 . The method of  claim 1  or  2  wherein the phosphate ester hydraulic fluid base oil comprises a mixture of tri alkyl phosphate, di alkyl aryl phosphate, alkyl diaryl phosphate, and triaryl phosphate.  
     
     
         4 . The method of  claim 3  wherein the dialkyl aryl phosphate and alkyl diaryl phosphate are selected from dibutyl phenyl phosphate, butyl diphenyl phosphate, diisobutyl phenyl phosphate, isobutyl diphenyl phosphate.  
     
     
         5 . The method of  claim 1  or  2  wherein the phosphate ester hydraulic fluid base oil comprises tri alkyl phosphate and tri aryl phosphate.  
     
     
         6 . The method of  claim 5  wherein the tri alkyl phosphate is a mixture of tri iso butyl phosphate and tri-n-butyl phosphate.  
     
     
         7 . The method of  claim 6  wherein the tri iso butyl phosphate constitutes about 30 to 80 wt % of the base stock, the tri n-butyl phosphate constitutes about 20 to 60 wt % of the base stock and the tri aryl phosphate constitutes about 3 to 15 wt %/o of the base stock.  
     
     
         8 . The method of  claim 5  wherein the trialkyl phosphate is tri isobutyl phosphate.  
     
     
         9 . The method of  claim 5  wherein the trialkyl phosphate is tri n-butyl phosphate.  
     
     
         10 . The method of  claim 5  wherein the triaryl phosphate is tri (isopropyl phenyl) phosphate, tri (tert-butyl phenyl) phosphate, or a mixture of the two.  
     
     
         11 . The method of  claim 1  or  2  wherein the fluid further contains one or more of an effective amount of a rust inhibitor or mixture of rust inhibitors and an effective amount of an antioxidant or a mixture of antioxidants.  
     
     
         12 . The method of  claim 8  wherein the fluid comprises a major amount of a fire resistant phosphate ester base stock and a mixture of additives comprising 
 from 2 to 10 wt % active ingredient, based on the total fluid, of a viscosity index improver,  
 from 4 to 10 wt %, based on the total fluid, of an acid control additive,  
 from 0.01 to 0.15 wt %, based on the total fluid, of an erosion inhibitor,  
 from 0 to 1.0 wt %, based on the total fluid, of one or more rust inhibitors,  
 from 0 to 3 wt %, based on the total fluid, of one or more antioxidants.