Chevron U.s.a. Inc.

Patricia V Lemay

John Michael Rosenbaum

Nancy J Bertrand

William Loh

A hydraulic fluid composition having excellent seal compatibility is prepared from an isomerized base oil is provided. The composition comprising (i) 80 to 99.999 wt. % of a lubricating base oil having consecutive numbers of carbon atoms, less than 10 wt % naphthenic carbon by n-d-M, less than 0.10 wt. % olefins and less than 0.05 wt. % aromatics, a molecular weight of greater than 600 by ASTM D 2503-92 (Reapproved 2002), a wt % total molecules with cycloparaffinic functionality greater than 25 and a ratio of molecules with monocycloparaffinic functionality to molecules with multicycloparaffinic functionality greater than 10; and (ii) optionally from 0.001 to 6 wt % of a viscosity modifier; and (iii) 0-10 wt % of at least an additive package. When used in operations, the composition results in an average volume change in a rubber seal of less than 3% and an average hardness change in the rubber seal of less than 1 pts. when tested under ASTM D 471-06 (SRE NBR1 at 100&#xb0; C., 168 hours).

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Vallejo, CA, United States of America

Patricia V Lemay