In hydraulic systems, hydraulic fluid is crucial to the performance and lifespan of equipment. Choosing the right hydraulic oil not only makes the equipment run more smoothly but also helps you reduce maintenance costs.
This article will explore the hydraulic fluid types, characteristics, applications, and factors to consider when choosing it, in order to help you find the best option for your equipment.
What is Hydraulic Fluid
Hydraulic oil is a medium used in hydraulic systems to better transmit power. It is mainly composed of base oils and some chemical additives. Furthermore, it can provide lubrication, reduce the wear of each component, and protect the components from corrosion to extend the service life of the hydraulic machinery.
4 Main Types of Hydraulic Fluid
Petroleum-Based Hydraulic Fluid
It is also known as mineral-based hydraulic oil. Because its raw materials are readily available and easy to manufacture, it has become the most commonly used hydraulic oil. The base oil comes from crude oil distillation followed by refining, and can achieve anti wear, anti corrosion, anti oxidation, anti foaming effects by adding various additives while also improving viscosity.
Its biggest advantage is cost-effectiveness. It can exert excellent lubrication and help you keep procurement and operating costs under control, meeting the needs of most industrial and automotive hydraulic systems.
However, you need to pay special attention to one point before choosing to use petroleum-based hydraulic oil. This oil is flammable, so it should not be used in high-temperature or high-pressure environments where safety risks are higher.
Since the base is petroleum, it cannot be fully biodegraded. This means that in the event of a leakage, it will cause serious pollution to the soil and water sources. And if you use it for a long time, some contaminants will be produced, which will lower oil performance and may shorten equipment life.
Water-Based Hydraulic Fluid
Water-based hydraulic fluid uses water as its base, mixed with additives or synthetic components. Because it contains a high amount of water, it offers strong fire resistance and is biodegradable, making it safer for both equipment and the environment.
But its lubricity is not as good as petroleum-based hydraulic fluid and synthetic hydraulic fluid. Especially in extremely low-temperature environments, water will freeze into ice.
Water-Oil Emulsion
It mainly includes two types: water-in-oil emulsion and oil-in-water emulsion.
In water-in-oil emulsion, water makes up the majority—often more than 80%. This high content helps hydraulic equipment release heat more efficiently. Nevertheless, it’s best for you to add some additives to improve its lubricity and enhance the stability of the liquid.
The proportion of oil in the oil-in-water emulsion is even larger, reaching over 60%. Although such a ratio ensures good lubrication performance, its fire resistance is much lower than that of water-in-oil.
Water Glycol Hydraulic Fluid
It is made by mixing ethylene glycol and water. It is relatively expensive but performs well in high-temperature environments. If you need to use water glycol hydraulic fluid in environments that require long-term exposure to chemical corrosion, you can add some rust or corrosion inhibitors to improve its resistance.
At the same time, you need to conduct regular maintenance and check to prevent contaminants from affecting lubrication performance.
Synthetic Hydraulic Fluid
Synthetic hydraulic fluid is made from chemical compounds. Compared with mineral oil, it is more expensive. Fortunately, it can maintain good viscosity and lubrication even under extreme temperatures. This makes them highly reliable for long-term use.
Phosphate Ester
Known for excellent lubrication, fire resistance, viscosity, and stability, and widely used in the aerospace field. However, it is very important for you to avoid using them on painted surfaces or seals, as it will corrode the paint and seals, and the viscosity will also decrease, leading to poor compatibility.
Polyol Ester
It shares the same advantages as Phosphate Ester and has excellent fluidity. But you need to be careful with material selection since they are not well-suited for silicone or rubber components.
Biodegradable Hydraulic Fluid
Biodegradable hydraulic fluid is derived from some renewable resources such as vegetable oil and synthetic esters. Therefore, it is non-toxic and can break down naturally, making it suitable for forestry and agriculture. It has good wear resistance and oxidation resistance, and its lubrication can match mineral oil, which can help you significantly reduce the failure rate of your equipment.
On the other hand, the cost is higher than mineral and synthetic fluid, so you need to plan for a larger upfront budget if you choose it. Also, under extreme heat, their stability will drop slightly.
Applications of Hydraulic Fluid
Aerospace
In the aerospace industry, the requirements for hydraulic oil are more stringent. The fluid must stay stable whether it’s exposed to low temperature at high altitude or extreme heat in brake systems. Moreover, the hydraulic oil must be fully compatible with the seals to prevent leakage or expansion.
For this reason, synthetic hydraulic fluids are commonly used. They deliver strong resistance to oxidation at high temperatures, remain fluid in the cold, as well as fire-resistance, ensuring flight safety.
Industrial
Hydraulic oil needs to undertake multiple functions such as lubrication and cooling in industrial equipment. The viscosity consistency and oxidation resistance of hydraulic oil are particularly important for your equipment. Machines such as injection molders and hydraulic presses often run under high temperature and continuous load. Once the oil quality deteriorates, it will lead to a decrease in efficiency or even shutdown failures.
By adding anti-wear additives, you can further reduce damage to molds, cylinders, and pumps. This not only cuts maintenance costs but also lowers the need for frequent spare parts replacement. Therefore, it is crucial to select the appropriate hydraulic oil for your production line. You will achieve higher production stability and a longer equipment lifespan.
Marine
Hydraulic systems are widely used in ship steering gears, lifting devices, and subsea equipment. You should be aware that even a small leakage of mineral oil at sea can cause serious pollution to the marine ecosystem. At the same time, the fluid must resist corrosion to keep water intrusion from reducing system performance. That’s why biodegradable hydraulic oil is often your best option. It breaks down quickly, meets environmental regulations, avoids penalties, and keeps your operations safe even under extreme conditions.
Food
In the food processing industry, hydraulic systems are also widely used, such as in food packaging machines, filling machines, and cutting machinery, etc. However, unlike other industries, the requirements for safety and cleanliness here are extremely high. You need to ensure that the hydraulic fluid won’t pose any health risks even if it accidentally comes into contact with food. Therefore, ordinary mineral oil or high-risk synthetic oil is often not suitable for use in food machinery.
At this point, you need to choose food-grade hydraulic fluid. Food-grade oils are tasteless, non-toxic, and highly resistant to oxidation and microbial growth, which can reduce system contamination caused by oil degradation. What’ s more, it has excellent lubricity, wear resistance and high-temperature resistance, meeting the requirements of continuous production.
Of course, you also need to consider the specific working conditions of the equipment. If the equipment operates under high temperatures and heavy loads, synthetic food-grade hydraulic oil can be selected to ensure stable viscosity and long service life. For light-duty equipment at normal temperatures, cost-effective food-grade mineral oils are sufficient.
Factors You Should Consider When Choosing Hydraulic Oil
Hydraulic Fluid Viscosity
Viscosity is one of the most key performance indicators of hydraulic oil. It directly affects how the fluid moves through your hydraulic system. When the viscosity is too low, lubrication becomes insufficient, parts wear out faster, and the risk of leakage increases. When the viscosity is too high, the flow resistance of the oil is too large, forcing the pump to work harder, which raises energy consumption and operating temperature.
Generally, you should match the viscosity grade to your working conditions and follow the equipment manufacturer’s recommendations. The right choice helps your machines run smoothly under different loads and environments.
Compatibility
Hydraulic fluid must be compatible with the seals, hoses, and other components in the system. If you choose improperly, seals may swell, shrink, or crack, leading to leaks and shutdown issues. Besides, you should pay attention to whether the additives in the oil work well together. Incompatible additives may produce foam and reduce the lubrication of your hydraulic fluid.
Therefore, if you are considering changing the type of hydraulic oil, you had better consult the manufacturer or relevant experts to confirm compatibility first.
Temperature
Temperature has a direct impact on the viscosity and stability of hydraulic oil. In a low-temperature environment, the fluid will thicken and make it harder to start your hydraulic system. At high temperatures, it becomes thinner, the lubrication will decrease, and even accelerate oxidation. The higher the viscosity index (VI), the less the viscosity changes with temperature. This means the oil can keep a steady performance in both cold and hot conditions.
That’s why you should always choose the right viscosity index based on your working environment to ensure stable operation.
Cost
Price is a factor that many enterprises care about, but being cheap doesn’t always mean cost-effective. High-quality hydraulic oil offers stronger oxidation resistance, better wear protection, and a longer service life. This helps you cut maintenance costs and reduce downtime. Although lower priced hydraulic oil can save you money upfront, premium oil delivers far greater value in the long run.
Conclusion
Whether you use mineral oil, water-based fluid, synthetic oil, or biodegradable options, you should decide based on operating conditions, safety, and environmental rules. If you’re looking to boost performance and cut risks, we can provide tailored hydraulic fluid solutions. Feel free to reach out—we’ll help you choose the option that best fits your business.
FAQ
Can different types of hydraulic oil be mixed together?
Not recommended for mixed use. Due to the different formulations of base oil and additives, chemical reactions may occur after mixing, creating sediments that may block precision valves. At the same time,mixing reduces lubrication performance, which can compromise system stability and shorten equipment life. If you replace the oil urgently, first fully drain the existing fluid and then clean the system before adding the new oil.
