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We were discussing in our previous posts about various hydraulic articles such as Basic principles of hydraulic system, Cost of hydraulic oil leaks, Common problem in hydraulic system and Cavitation in hydraulic system.

Today we will see here in this post about the basic tasks of hydraulic fluids, so let us come to the point where we will come to know about the various basic tasks of hydraulic fluids.

If we look the theory, any type of liquid could be used for transferring the pressure energy. But can we select any type of liquid in hydraulic units? Your answer will be no and that’s correct answer. There are various characteristics; those are very important and much required for a fluid to be considered as hydraulic fluid.

I have one question; can we use water in hydraulic system as hydraulic fluid? We will surely say no, never etc. Because there will be various issues if water is considered as hydraulic fluid in hydraulic unit such as corrosion, boiling point and freezing point , lower viscosity, poor lubrication etc. I am sure there will be many more reason and I will request to my readers to suggest me in comment box.

So, let us see now the key functions of hydraulic fluid

Power transmission

Hydraulic fluid will have to transfer the power in terms of pressure energy throughout the hydraulic unit to actuate the actuator in order to perform the specified task smoothly. Hydraulic fluid must be incompressible, however we use hydraulic accumulator in hydraulic unit to provide the characteristics of incompressibility in hydraulic system.


Hydraulic fluid must have ability to lubricate each moving parts of device in hydraulic unit and simultaneously to protect the components of hydraulic unit against corrosion, oxidation, friction, rust, wear and tear.


As we have discussed in our previous posts that loss in pressure energy will result the production of heat in hydraulic system, we will have to remove this heat for smooth operation of hydraulic unit and the task of this heat removal process will be completed by circulating hydraulic fluid.

Sealing Medium

There are various applications in hydraulic system, where hydraulic fluid will have to provide the suitable sealing.
Image courtesy : Google 

Hydraulic fluids, those are mostly used in industries, are 46 and 68 grades. There are two more grades i.e. 22 and 32. I have heard about these hydraulic fluid grades but I have not seen in applications. If you have seen the application of hydraulic fluid of grade 22 or 32, please share in comment box.

Such hydraulic grade fluid, as we have discussed above, with mineral oil base will be used as hydraulic oil for hydraulic units. If our hydraulic units are installed at a location where there are possibilities of catching fire, in this situation we should not prefer to use hydraulic fluid with mineral oil base in hydraulic units but also we should use synthetic hydraulic oil.

To secure the information’s about various properties of hydraulic fluid and classification of hydraulic fluid or oil, please read below mentioned posts.

Also read

Do you have any suggestion? Please write in comment box.

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