Comparative evaluation of several hydraulic fluids in operational equipment, a full-scale pump stand test and the four-ball wear tester. Part II. Phosphate esters, glycols and mineral oils

A sequential four-ball wear test which has been designed and used to predict pump test and vehicular hydraulic system performance has been used to evaluate a series of mineral oil, water glycol and phosphate ester base hydraulic fluids. Specifically, run-in wear, steady-state wear and the effectiveness in forming antiwear coatings are evaluated by this technique. Steady-state wear and scuffing appear to be important factors in establishing correlation with pump stand test and vehicle hydraulic system performance. Vickers vane pumps are utilized in both of the hydraulic systems. The results of this study show a good correlation of the four-ball wear data at 10 kilogram load with the performance in both systems. Mineral oil formulations containing effective antiwear additives show good performance in all systems, while the water-glycol and phosphate esters show less effective wear protection. Increased wear problems with increasing test temperature in the four-ball wear tester have been demonstrated for both phosphate esters and the water glycol fluids.