Since then emulsions and synthetics have been added to the choices available for hydraulic systems. It should be noted that under the right conditions these fluids ignite and are not fireproof. Viscosities are comparable to petroleum-based fluids. Operating temperatures must be kept below 140 F to prevent excessive water evaporation and control viscosity. Seals and paints may be affected and pumps may have to be derated to achieve a reasonable service life.
Additives provide for the properties desired in hydraulic fluids.
Over the past several years there has been an increased interest in hydraulic fluids that, if leaked, would be less detrimental to the environment. Most petroleum based and synthetic oils degrade and do not persist in the environment. To achieve better biodegradability and virtually no toxicity, vegetable oil-based hydraulic fluids have been developed over the past 5 yr. Their performance approaches that of petroleum-based fluids. Vegetable oil-based fluids have a very high viscosity index, which is valuable in applications where temperatures vary or are elevated.