Advisor
Hydraulic fluids perform a wide range of tasks. Depending on the application area, these may vary further. Basically, however, the following are the main tasks of hydraulic oils:
- Transmission of power in the hydraulic system
- Lubrication
- Protect against corrosion, wear, and deposits
- Cooling and cleaning In addition
The following properties are essential in hydraulic oils:
- Air and water separation capacity
- Foam behavior
- Filterability
Transmission of power in the hydraulic system
Hydraulic oils must move machine parts under pressure. Usually, the oil is pumped through a pipe to move a piston at the end of the pipe. Thanks to the lever law, a small pump output (small input force) can generate a large output force.
Lubrication
Hydraulic oils must also lubricate the movable parts of the hydraulic system so that they can be moved with reduced force and the sliding metal parts are protected from abrasion. The ISO viscosity is important here as well. Depending on the application, a different viscosity is required. There are also multi-range hydraulic oils that have an improved viscosity-temperature behavior thanks to certain additives.
Protect
The task of the hydraulic oil is to prevent corrosion. Corrosion is defined as the decomposition of a metal caused by oxidation. By adding corrosion inhibitors to hydraulic oils, the oil forms a protective layer on the metal parts against water, oxygen, and other corrosive substances, thus protecting the engine.
Cooling and cleaning
On the one hand, the task of the hydraulic oil is to cool the hydraulic system by absorbing and removing the heat generated. It also transports the dirt generated such as metal chips or other contaminants to the oil filter.
Air and water separation capacity
There is a little air in every hydraulic oil. If this proportion becomes too high, there is a danger of the "diesel effect" in which the mixture of oxygen-rich bubbles and oil ignites and produces soot particles, darkening the oil.
Water particles also interfere with the functionality of the oil. Unlike engine oil, where any water particles are destroyed in the combustion chamber, they remain in the hydraulic oil and accelerate the formation of corrosion and cavitation. Therefore, the water should separate from the oil and can be removed. However, there are also systems in which so-called HLPD or HVLPD Oils are used, which distribute the water particles in the entire oil into tiny particles and thus neutralize them to a certain extent.
Foam behavior
Foam is usually caused by bubbles that form inside the oil but do not burst when floating on the oil. If such bubbles accumulate, foam is formed. This is bad for the hydraulic system, as it prevents the heat from being dissipated and it can also ooze out of the smallest system openings. The resulting loss of oil then leads to a lack of lubrication, which causes wear. Often, excessive use of additives promotes the formation of foam. An antifoam additive is therefore mixed into the production of hydraulic oils to prevent the occurrence of foam.
Filterability
In today's hydraulic systems, either built-in or mobile filters are always used. Their purpose is to free the oil from impurities and thus ensure the longest possible lifespan of the oil, which is crucial for the performance of the hydraulic system.
The filterability of hydraulic oil defines the change in differential pressure when flowing through a filter. For example, clogging of the filter can lead to an increase in pressure during flow, which must be prevented at all costs.
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More questions about Hydraulic Fluid
Due to this variety of tasks, there are different hydraulic oils depending on the application area. The DIN 51524 standard classifies hydraulic oils by defining minimum requirements.
If a hydraulic oil foams, this can be prevented to a certain degree with an antifoam additive. However, it is important to note that more of this additive does not equate to better foaming behavior. Therefore, the unauthorized use of antifoam additives is rather discouraged and it is recommended to change the hydraulic oil completely.
Foam in the hydraulic system is known to be something that is not desirable. The reason for this is that the foam can cause the oil temperature to heat up unnecessarily. In addition, the foam can cause oil loss, which leads to insufficient lubrication.
No, engine oils should not be used in the hydraulic system because they are designed for different tasks and thus cannot normally perform the tasks of the other.