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The Importance of Hydraulic Fluids

February 16th, 2011

hydraulic-oil-engines.jpgA very important element in any industrial hydraulic system is the hydraulic fluid. It is a means for transmission of energy, a sealant, a lubricant, and a heat transfer medium.

This industrial petroleum base fluid is more complex than ordinary oil. Commonly, paraffin compounds present in oil crystallize at low temperatures. This process increases viscosity of the fluid and accumulation of deposits. Exposure to air induces oxidation, carbon formation, acidity, and poor lubricity. Metals such as copper and lead present in the system aggravate this oxidation process at high temperature levels. Accumulation of air bubbles reduces lubrication and causes erratic operation. Hydraulic systems operate with high pressure, thus the components of the pumps are prone to welding along mating surfaces.

Oil is the life blood of a hydraulic system. Hence, ingredients are added to modify its characteristics suitable for hydraulic operations. These chemicals are called additives. There are additives that elevate the viscosity index of the fluid, usually 90 or above. These chemicals prevent thinning of oil at high temperatures and waxing at low temperatures. Anti-oxidation additives slow down oxidation process; hence, the right amount must be applied in an environment with high temperatures and high oxygen supply. Anti-corrosion additives either form protective films along the metal surfaces or neutralize acidic materials in the system. Anti-wear additives are used for extremely high pressure or temperature applications. Anti-foam additives collect tiny bubbles, combining them to rise and eventually burst at the surface.

Hydraulic fluids are preferred in the industry to be fire resistant but petroleum base fluids are highly combustible. To address this problem manufacturers develop different types of fire resistant fluids. These are synthetic base fluids, oil-in-water fluids (soluble oil), water and antifreeze fluid, and water-in-oil fluids (invert-emulsion). Synthetic fluids are petroleum fractional parts combined with chlorinated hydrocarbons or phosphate esters. Components of the hydraulic system utilizing synthetic fluids require special seal materials. Water and antifreeze fluids are 40% water and 60% glycol mixtures. Oil-in-water fluids are mixtures of oil in dominant water, while invert emulsion fluids are mixtures of water in dominant oil.

Proper selection of hydraulic fluids is important for every application. Regular inspections, adherence to manufacturers’ specifications, and implementation of recommended tests and maintenance activities of equipment will insure efficiency and reliability of its hydraulic system.


This article on hydraulic fluids was supplied by an anonymous Content Content author with the pseudonym of “a voice in the wilderness”.


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