What are the characteristics of good hydraulic oil?

Hydraulic systems are systems where energy is transmitted through fluids. These fluids are called hydraulic fluids and have various applications such as agriculture, construction, forestry, mining, steel, aviation, etc.
In addition to acting as a power transmission medium, they also have sealing, lubricating, and cleaning properties.
In this brief guide, we discuss the main characteristics of high-quality hydraulic oils.
Optimal viscosity
Viscosity indicates the fluid’s resistance to flow. Only by maintaining the optimum viscosity in hot and cold temperatures can they transmit power effectively. If the hydraulic oil has a low viscosity, it means that it is too diluted. In this case, it is not able to protect and seal efficiently and increases the risk of wear and tear. On the other hand, when the hydraulic oil has a high viscosity, it is more difficult to pump through the system, reducing overall efficiency.

Note that hydraulic oil viscosity requirements vary depending on the type of pump used in the hydraulic system. There are three types of pumps – vane, piston and gear.

Low compressibility
Fluctuations in working pressure and temperature affect the volume of hydraulic fluids. As the temperature increases, the density of oil decreases and the volume of hydraulic oil increases. The compressibility of hydraulic oil indicates the change in fluid volume caused by pressure fluctuations.

High compressibility may cause severe performance problems in high pressure fluid systems. Some of them include servo failure, cavitation and metal fracture and power loss. That is why it is important to choose hydraulic oils with low compressibility.

Oxidation stability
Oxidation stability refers to a chemical reaction that occurs when oxygen and hydraulic fluid mix.

The rate of oxidation grows over time and is accelerated by high temperatures, water, acids and catalysts. In addition, it affects the useful life of a lubricant and causes oil degradation and sludge formation.

Of course, the rate of oxidation depends on various factors such as the type of base oil, the quality of the oil, and the additive package used. Synthetic fluids typically have better oxidation stability and can operate at higher temperatures than their mineral counterparts. To improve the oxidation stability of the oil, antioxidants are used in additive packaging.

Thermal stability
Thermal stability refers to the ability of hydraulic fluids to resist degradation at high temperatures. It is essential for the performance and efficiency of all mechanical systems.

Antiwear additives have a limited shelf life, meaning they degrade over time. This may lead to sludge formation which can clog filters, reduce oil flow and increase downtime. In addition, anti-wear additives decompose at very high temperatures. This leads to the formation of acids that attack and damage the metals in the hydraulic system components.

Thermally stable hydraulic oils reduce these performance problems and extend the life of hydraulic system components.

Hydraulic stability
When water comes into contact with your hydraulic fluid, it changes its additive system, leading to the formation of acids that attack metals. In addition, fluids with low hydraulic stability are hydrolyzed. They create insoluble salts that can clog filters and valves, preventing the uninterrupted flow of oil. Lack of lubrication and power transmission may cause severe damage to the hydraulic system.

This is why you should choose hydraulic oils with high hydrolytic stability, meaning they resist chemical degradation in the presence of water. They increase the overall performance and lifespan of your hydraulic machinery and equipment.

Anti-foam properties
Foaming is caused by air entering the hydraulic oil through the reservoir or air leakage. When the fluid is under high pressure, it may have many scattered air bubbles. However, when it is not under pressure, those air bubbles expand and begin to form foam.

Foam is one of the biggest enemies of hydraulic systems because it compromises their efficiency and lubrication. The solution to the problem of foaming is obvious – choose hydraulic oils with anti-foaming additives.

Anti-corrosion properties
When water mixes with hydraulic fluids, it increases corrosion of hydraulic system components. In addition, it accelerates the breakdown of additives in the oil formula and forms chemicals that may damage the yellow metals in the hydraulic system.

This is why quality hydraulic oils contain rust and corrosion inhibitors. They prevent water and other chemical components from attacking metal surfaces.

Use of low-quality hydraulic fluids
Using low-quality or inappropriate hydraulic fluids may reduce the life of your heavy industrial machinery. It leads to frequent device breakdowns, costly repairs and increased downtime. That’s why it’s so important to choose high-quality lubricants that match the needs of your hydraulic system.

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