Hydraulic fluids can be compared to blood in the body of hydraulic systems, and given its importance I deemed it necessary to devote an entire article to these fluids. As the name itself suggests, hydraulic fluids refer to those group of fluids which are used in hydraulic systems of innumerable machines including but not limited to aeroplanes, industrial lifts, braking systems and so on. Depending on the type of machinery and its intended purpose the hydraulic fluids used in the same could range anything from water, water in conjunction with other compounds, oils and silicon fluids.
Petroleum based hydraulics fluids
Petroleum based hydraulics fluids have been in use for a long time and are quite popular in the industry mainly because of their near-perfect characteristics required for hydraulic operations. However whatever is petroleum based certainly has a tendency to catch fire or explode if the temperature or other conditions of optimum safety are exceeded, which is not very uncommon in industrial scenarios. Hence this renders these otherwise useful petroleum based hydraulic fluids to be susceptible to the risk of catching fire or even exploding under the right (rather the “wrong") environmental conditions. But the main advantages of such fluids are their strong anticorrosion characteristics which are generated by adding specific additives while manufacturing them.
Because of the drawbacks of petroleum based hydraulic fluids with regard to fire and explosion hazards, nowadays phosphate ester based hydraulic fluids are being increasingly used in situations where risk of heat is present, but they have the other disadvantage of attacking the paints, gaskets and sealings of the equipment in which they are used. Hence this calls for special grade materials in manufacturing those parts which means increased costs of operation and maintenance.
Fire resistant hydraulic fluids can also be water based instead of being based on phosphate ester. These are usually mixtures of water with either some synthetic base or glycol. Apart from these yet another variety of fire resistant hydraulic fluids come in the form of silicone based fluids. These also have strong anticorrosive characteristics.
Many times it is not only fire resistance but other features which govern the choice in a given situation. For example in case of hydraulic fluids used in the aviation industry weight is serious consideration, of course subject to optimum combination of other properties as well.
Since environmental concerns weigh heavily over any substance in industrial use currently, it is also important to know something about the environment hazards involved in the use of hydraulic fluids. Certain types of hydraulic fluids which are not biodegradable certainly can cause damage especially if they get into the environment in an unplanned manner, such as during oil spill from a ship. Yet no observable effects have been seen of hydraulic fluids on human body, except of course under circumstances when they might get swallowed accidentally or get in contact with sensitive parts such as eyes, though agencies such as OSHA (Occupational Safety and Health Administration) have set their limits on the weekly exposures of petroleum based substances on workers.
Read more about hydraulics:
Hydraulic Fluid - Why the Fuss About Being Incompressible?