Synthetic Hydraulic Fluids

Synthetic fluids on the whole have excellent fire resistant properties. Many of these fluids may be used at high temperatures, and some are quite expensive. Such fluids are named after their base stocks, that is, the predominant material, and their formulations are chemically involved.

Phosphate ester base fluids are used in both aircraft and industrial applications. Their thermal stability is rather poor for sustained operation at temperatures in excess of 300°F, but their lubricity is excellent [4], These fluids are solvents for many types of paints and seals so that care must be used to ensure compatibility with system materials. Examples of commercially available fluids include Skydrol 500A, Pydraul F-9 and 150, Cellulube 220, Houghto-Safe 1000 series, and Nyvac 200.

Silicate ester base fluids have excellent thermal stability which permits their use as high temperature fluids, but they have poor hydrolytic stability. Commercial fluids include Monsanto OS-45 and Oronite 8515. The halogens of chlorine and fluorine are united with hydrocarbons to form fluid base stocks of chlorinated hydrocarbons and fiuorinated hydrocarbons.

Such fluids have high thermal and oxidative stability required for high temperature applications, but relatively high freezing points limit their use at low temperatures. Commercial chlorinated hydrocarbons include Aroclor 1000 series and Pydraul A-200.

Silicone base fluids have excellent viscosity-temperature characteristics but are limited by their lubricating ability. Examples of commercial silicone fluids are Dow Corning F-60 and Versilube F-50.

The water base fluids are fire resistant and compatible with standard seal materials but have poor lubricating ability. tVaier glycols are a formulation of water and a glycol, which thickens the fluid to increase viscosity,
with various additives to improve lubricity and corrosion resistance. Commercial water glycols include Ucon Hydrolube 100 series, Houghto- Safe 600 series, and Cellugard. Water-in-oil emulsions are formed by a stable suspension of water particles in a hydrocarbon oil. However, the water and oil does tend to separate and, if allowed to stand, agitation is required to maintain the dispersion of water in the oil. Checking the fluid while in use is desirable to ensure that the water content is at a satisfactory level. Commercial examples are Shell Irus 902, Sunsafe, and Houghto-Safe 5000 series fluids. Although their high temperature range is limited because of the water content, the water base fluids offer a satisfactory and economical
industrial hydraulic fluid when properly used.

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