How Do You Know If You're Using The Right Hydraulic Oil?

How Do You Know If You’re Using The Right Hydraulic Oil?

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Maybe you are already using hydraulic oil, maybe you are not familiar with hydraulic oil, this article not only introduces hydraulic oil, but will teach you how to choose the correct hydraulic oil for your equipment.

What is hydraulic oil?

Hydraulic oil is a multi-functional fluid, usually, the composition of hydraulic oil is mineral oil. It can be used as a power transmission medium or as a sealing medium and lubricant and has certain fire resistance. Common hydraulic oils in life include brake fluid, power steering fluid, aircraft hydraulic system, transmission oil, etc. Commonly used in excavators, aircraft, automobiles and other mechanical products, it can be said that hydraulic oil is one of the most crucial lubricants in our lives. The three major areas of hydraulic oil are stationary, mobile and aviation hydraulics. When the right hydraulic fluid is selected, it can save energy and reduce wear and tear on machine components, which will save you maintenance costs and extend the working life of your equipment.

Types of hydraulic oil

Hydraulic oil is also similar to your engine oil and can be divided into mineral hydraulic oil and synthetic hydraulic oil. The former is an extract of petroleum, and the latter is synthetically manufactured. In addition, the fire protection applications of hydraulic fluids have been introduced before, and are generally used in such environments with refractory fluid-based hydraulic fluids. Below we will introduce the first two types of oils.

The low cost of such hydraulic fluids can enhance their qualities with additives. Just like the additives in 90/92 gasoline. Depending on the quality of additives and base oils, they can even achieve the same high performance as synthetic products, changing product stability, corrosion resistance, wear resistance, the temperature stability of viscosity, etc. But they are less tolerant to temperature changes where performance changes.

The reason for the birth of this type of hydraulic oil is to overcome some of the shortcomings of hydraulic oil. They are chemically produced, and they perform exceptionally well at high temperatures compared to mineral oils, with good oxidative stability and biodegradability. However, the cost of this hydraulic oil is generally higher than that of mineral oil, and it has higher toxicity.

How does hydraulic oil affect your machine performance

The fluid of the hydraulic system and the equipment itself are closely related. Together they determine the efficiency and longevity of the system. Generally speaking, the key elements of hydraulic oil are fluid type and viscosity. Hydraulic systems operating with poorly matched fluids experience the following problems:

  • Over-lubrication, resulting in reduced productivity.
  • Lack of lubrication leads to reduced mechanical excessive wear, severely reducing the service life.
  • Equipment corrodes, produces sludge and causes mechanical failure
  • Next, we will tell you several major elements for choosing hydraulic oil

The crucial properties of a Good Hydraulic Fluid

In order of criticality, the most important factors for selecting hydraulic fluids are: viscosity index, anti-wear properties. In addition to some industries, there are foaming properties, anti-rust and anti-corrosion properties, air release properties, and oxidation stability properties that need to be considered.

  • Anti-wear performance: Anti-wear additives will form a thin oil film on the metal surface. If the oil film is too thin, the metal will be in direct contact with the metal, resulting in excessive wear of the equipment, reducing the life of the equipment and increasing the maintenance interval. If the oil film is too thick, there will be problems with slow movement and reduced mechanical efficiency.
  • Viscosity Index: A value that expresses the effect of temperature on viscosity; high VI hydraulic fluids maintain their viscosity relatively well with changes in temperature. But the cost will be higher.
  • Oxidative Stability: Oxidative stability refers to the hydraulic fluid’s resistance to thermal degradation due to chemical reaction with OS2. A high-quality hydraulic fluid must contain additives that counteract the oxidation process, improve stability, and extend fluid life. Otherwise, the quality of hydraulic oil will deteriorate rapidly and affect machine life and working efficiency.
  • Air Release: The ability of the oil to release enclosed air. Air can cause system inefficiencies and cavitation.
  • Foaming: After the oil is stirred and aerated, it will foam. This is a common problem in hydraulic systems. This can seriously affect the lubricity of hydraulic oil due to the poor compressibility and lubricity of foam. Adding a foam inhibitor can change the surface tension of the bubbles, making them easier to burst.
  • Filterability: Water reacts with additives in hydraulic oil to form oil-insoluble contaminants. These contaminants can settle out of the lubricating oil and clog components such as filters, valves, etc., resulting in reduced or blocked oil flow, which can ultimately lead to serious consequences. Hydraulic fluids are designed to be filtered using modern filtration systems without fear of additives being depleted or removed from the system. This allows the system to remain unobstructed.
  • Emulsification Resistance: The ability to release moisture, which is vital in humid climates. Water entering the hydraulic system can mix or emulsify with the hydraulic oil. If this “wet” fluid circulates in the system, it promotes rust and corrosion. It is therefore necessary to rapidly separate or break the water. Hydraulic fluids require the addition of demulsifier additives to facilitate the separation of water and hydraulic fluid.
  • Rust and Corrosion Protection: In many equipment, water enters the circulation as condensate or contaminants and mixes with hydraulic oil. We all know that water can cause hydraulic components to rust. In addition, water can chemically react with some additives to form substances that are aggressive to metals. Hydraulic fluid formulations must contain rust and corrosion inhibitors to prevent this from happening.


In summary, this article summarizes several key points for choosing the best hydraulic oil:

  • Choose the correct viscosity for a given operating temperature
  • Choose the right anti-wear additive: zinc-containing or zinc-free anti-wear protection additive.
  • Choose an appropriate viscosity index. In extreme temperature changes or harsh operating conditions, high viscosity hydraulic fluids are the best choice. But too high viscosity can reduce operational efficiency.
  • When the industry has special needs, choose the additive hydraulic oil that meets the needs.

If you still want to learn more about hydraulic oil or have a need for it. Please feel free to contact us.

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