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Hydraulic fluid: types, classification and composition
Hydraulic fluid: types, classification and composition

In the installation and maintenance of technical mechanisms, the greatest attention is paid to functional elements, auxiliary equipment and various fixation and support systems. But at the same time, the quality of equipment operation largely depends on technical fluids. They perform different functions, but all of them ultimately come down to one task - to extend the service life of the serviced object. A special place in this group is occupied by hydraulic fluid, which also acts as a functional component, putting pressure on the working elements of the mechanism.

fluid hydraulic pressure

Where are hydraulic fluids used?

Oils of this type are used in various technical devices and mechanisms. A classic example of their application is pipeline valves. By themselves, hydraulic devices are widely used in various fields of industry, manufacturing and construction. These can be press machines, units in factory lines, hydraulic processing systems, etc. It is important to note that hydraulic fluid can also be used in household equipment. Some models of pneumatic stations, pumping equipment and power units may also use suchliquids. Moreover, the functions of this type of oil are also different - they should be considered in more detail.

Fluid functions

The main task of the hydraulic fluid is to transfer pressure to the working component of the system. It can be a piston or a valve, the main thing is that the volume of oil acts as a dynamic force transmitter and at the same time performs a number of auxiliary functions. For example, as already noted, technical oil provides lubrication of the rubbing elements of the working system, extending their life. Special tasks may be required depending on operating conditions.

For example, if the unit is planned to be operated in an environment subject to thermal effects or close contact with moisture, then the hydraulic fluid is replaced with a composition with suitable protective qualities. In this case, the technologist will recommend an oil with anti-corrosion properties and thermal stability. At the same time, by default, each composition of the hydraulic fluid provides for cleaning. Pipelines are regularly washed, as a result of which their internal surfaces get rid of precipitation and other destructive substances.

Properties of oils for hydraulic systems

hydraulic fluid replacement

The quality of the above functions is determined by the properties of a particular composition. The basic performance characteristics of hydraulic fluids include thermal resistance, viscosity, inertness, and density. But specialworking qualities, including protective ones. For example, anti-corrosion allows you to withstand liquid and humid environments without negative rusting processes. The hydraulic resistance of the liquid is also important, which determines the intensity of the working function of the composition. That is, the lower the resistance index, the easier it is to transfer the force from the power unit. As a result, less energy is spent to ensure the operation of the installation. Another thing is that the achievement of optimal resistance indicators is rarely achieved without loss in other technical and physical qualities of hydraulic oils.

Classifications of hydraulic fluids

hydraulic brake fluid

Specialists classify such liquids according to several criteria. For example, the main division is carried out on the basis of purpose - a separate place in the assortment is occupied by hydrostatic and hydrodynamic compositions. Liquids are also released depending on the application. In particular, ISO 15380 marked lubricant formulations provide fast biodegradation processes. There are also modifications that are more environmentally friendly. They are often used in food industry units. Hydraulic fluid labeled STOU is also common. It is usually involved in the maintenance of mobile systems. At the same time, a wide group of auxiliary fluids are in demand, which do not work in the main part of the hydraulic piston mechanism, but are used in the technical support of individual components, such as couplings, bearing groups andconverters.

Varieties of fluid based on working qualities

what kind of hydraulic fluid

In this classification, it is appropriate to consider three main groups of hydraulic oils. The first is represented by the main compositions, which are characterized by balanced indicators of viscosity, compressibility and pressure. It can be said that these are typical universal means of providing a liquid hydraulic function. The second group covers products that are resistant to oxidation processes. This includes thermally resistant types of hydraulic fluids that are able to circulate under high pressure, in contact with metal surfaces, water and air. The third group provides for a more perfect performance of the thermal protection function. These are compounds that are not subject to fire hazards even when in close contact with sources of fire.

Hydraulic fluid formulations

The output product is usually concentrates based on industrial oils and additives. A classic example is one made with mineral oil and emulsifiers, and diluted with rust inhibitors. Actually, such a combination in itself can serve as the basis for the preparation of more technological modifications, which can also be combined with a huge range of elastomers. For example, to increase the hydraulic pressure of a fluid, manufacturers introduce sealants into formulations. And vice versa, if you need to achieve a higher degree of elasticity of the working component, emulsionlubricating oils.

Basic foundation

hydraulic fluid

Paraffin compositions, naphthenic mixtures and various combined solutions can be used as base mineral oil. There are also special modifications with improved basic working qualities. These are synthetic fluids that use hydrocracking components, ester compounds and polyglycols, which are most often used for fire-resistant mixtures. Natural bases from which biodegradable hydraulic oils are produced also find their application. Liquids of this type may contain plant-derived products that are environmentally friendly.

Regardless of the type of base oils, the quality of their purification also matters. There are different categories, differing in the degree of preliminary preparation of the composition. There are mixtures of coarse cleaning, and there are also oils that have undergone repeated filtration. This is not to say that the second option will be the best in all use cases. In some areas, it is liquids that are optimally manifested, which are based on a rough elemental combination.

Additives and fluid modifiers

It is often the additional components that play the determining role in performance. They are mutually exclusive or complementary, so it is impossible to get a completely universal tool suitable for any need. To varying degrees, the base base can be given such properties as anti-corrosion, aging resistance,extreme pressure and anti-wear properties.

In this case, the additives are divided according to the nature of the application. There are components that are added as an addition to the mineral base oil, and there are also surfactants. For example, hydraulic brake fluid is obtained as a result of the inclusion of surface friction modifiers, which can be introduced into the composition already during the operation of the mechanism.

Basic oil additives are usually included at the factory. This category includes antifoaming elements, antioxidants, etc. Active additives against this background will be beneficial in that they do not require special treatment of the liquid after addition.

How to choose hydraulic fluid?

hydraulic oil fluids

To a large extent, the choice of one or another composition is determined by the operating conditions. In particular, the range of operating temperatures, type of hydraulic system, pressure, environmental requirements and external influences should be taken into account. It is desirable to pay special attention to the viscosity index. If the task is to reduce leakage and increase sealing, then mixtures with a minimum level of viscosity should be preferred. The temperature of the working environment is also taken into account in a separate order. When deciding which hydraulic fluid to choose for a stationary system, you can give preference to compositions designed for a regime of 40-50 ° C. For mobile and dynamic systems, highly specialized fluids are often selected.

How to change hydraulic fluid?

Firstturn it is necessary to open access to the liquid storage tank, as a rule, these are special metal tanks. Further, space is freed up for work with the communication infrastructure. Usually, the supply hoses are supplied with clamps, which should be unclenched. This will check the hydraulic fluid level, pressure and general condition. Next, the oil is pumped out. This operation can be performed using syringes or pumps with compressors, depending on the design feasibility.

Then you can start pouring a new mixture. This operation is also performed using an improvised tool or directly if it is possible to disconnect the supply hose. Proper hydraulic fluid replacement is also done with air evacuation. Excessive airing can lead to losses in unit efficiency, so removing excess gas mixtures is indispensable.


liquid hydraulic resistance

Hydraulic mechanisms often perform critical tasks that require the connection of high power. In turn, the hydraulic fluid acts as a full-fledged functional component of such systems, ensuring the stable operation of the units. With the right choice of this oil, maintenance personnel will be able not only to extend the life of the operating installation, machine or tool, but also to increase the energy efficiency of the equipment. This is due to the fact that the same indicators of the resistance of the working fluid can increase or alleviate the load on the drive mechanism,which will directly affect the amount of resource consumed.

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