Hydraulic fluid serves as the energy transfer medium within the hydraulic system, circulating throughout the mechanical equipment. It is incompressible and does not easily deform under pressure.
In this article, we will provide a detailed explanation of what hydraulic fluid is, its functions, and its 15 key properties. This will enable you to better choose the best type of hydraulic fluid for your project, generating greater economic benefits.
What is Hydraulic Fluid?
Hydraulic fluid, also known as hydraulic oil, consists of water, a base oil, and additional additives. It is considered a kind of non-compressible, engineered medium. When you put force into one end of a hydraulic system, it generates pressure and then travels through the hydraulic fluid. Finally, the fluid works to provide motion or power for driving the whole system.
What is The Function of Hydraulic Fluid?
The primary function of hydraulic fluid in your hydraulic system is to transmit energy. Due to its incompressibility, it helps your system convert mechanical energy into hydraulic pressure. And the fluid is then evenly distributed throughout the entire hydraulic system. The generated hydraulic pressure drives hydraulic pistons or hydraulic cylinders, enabling the operation of other equipment components.
Hydraulic fluid also functions as a lubricant for internal components. It ensures smoother operation between hydraulic components while you are operating the system. Without this lubrication, metal parts would friction against each other, significantly accelerating wear and tear. This would lead to a reduction of your hydraulic equipment effective power.
Hydraulic fluid also serves as the final seal for your hydraulic system. While O-rings and other seals already provide sealing functions, hydraulic fluid offers the last line of defense for system sealing. It fills microscopic gaps within the system, preventing external contaminants like dust from entering. This ultimately maintains stable pressure within your hydraulic system, ensuring continuous and reliable operation.
15 Properties of Hydraulic Fluid
Next, you will learn about the various properties of hydraulic fluid. We have categorized them into 15 different types. After reviewing these, you will undoubtedly gain a deeper understanding of hydraulic fluid.
Viscosity
The higher the viscosity of hydraulic fluid, the thicker the fluid becomes, and the greater the flow resistance it encounters. You need to carefully control the viscosity of your hydraulic oil. If the viscosity is too high, the fluid will become completely immobile, ultimately leading to dangerous consequences. Your equipment may be shut down and then could cause damage to your interests.
You require a fluid with appropriate viscosity to ensure your machinery operates smoothly. This fluid aids in effectively sealing your hydraulic equipment. It also forms a lubricating film on the metal mechanical components within the hydraulic system. This film enables your equipment to run more efficiently.
It’s noted that hydraulic oil viscosity is inversely proportional to temperature. Higher temperatures reduce viscosity, potentially causing internal leaks. Conversely, as temperatures drop, viscosity increases, leading to the dreaded outcome. That could obstruct fluid flow and ultimately lead to equipment shutdown.
The viscosity level of hydraulic oil also determines whether it can smoothly traverse the narrow passages in the system. It further influences the oil’s ability to navigate sharp turns.
Lubrication
The lubricating property of hydraulic fluid is to reduce friction between metal components in the hydraulic systems. Meanwhile, it could protect system parts from wear.
If you use hydraulic fluid with poor lubricity, you may find that it will decrease the efficiency of your hydraulic system and eventually shorten the lifespan of your machinery.
Hydraulic fluid with excellent lubricating properties forms a robust film on surfaces it contacts. This action could ensure your components remain protected from abrasion. This provides you with superior lubrication for moving parts and minimizes functional degradation caused by wear.
Minimum Compressibility
The incompressibility of hydraulic fluid enables efficient operation of hydraulic equipment. Since all hydraulic systems adhere to Pascal’s principle. So the minimal compressibility of hydraulic fluid makes it the optimal medium for transmitting force. It also facilitates the application of smaller forces over larger areas to generate greater forces. This approach helps reduce the cost of your initial power source.
Demulsibility
A qualified hydraulic fluid possesses the ability to resist emulsification, enabling it to rapidly and completely separate from water when contaminated. If water becomes incorporated into the hydraulic fluid, it can lead to corrosion of hydraulic components and potentially damage your critical machinery.
Fire Resistance
The fire resistance of hydraulic fluid can significantly reduce the risk of your hydraulic equipment catching fire or burning. In high-temperature or hazardous environments, such as coal mining and hot metal processing applications, the hydraulic fluid used faces a heightened fire risk.
Using fire-resistant hydraulic fluid is critical for the safety of both you and your equipment.
Foam Resistance
Because air is compressible, foaming will definitely occur when air mixes with hydraulic fluid. Therefore, strong foam resistance is also a crucial aspect of hydraulic fluid. The primary cause of hydraulic fluid foaming and overflowing from your reservoir is likely contamination of the hydraulic fluid. Other possible causes include poor system design and cavitation.
The best way to eliminate foam formation is to ensure your hydraulic system is completely sealed. If foam has already formed in your hydraulic system due to air ingress, you can also follow the methods below to minimize the damage as much as possible.
Surface foam appears on hydraulic lines. You can eliminate it by using defoaming additives. These additives limit foam from entering the system.
Entrained air is air absorbed by the system. You need to pay close attention to the equipment design viscosity. You also definitely use suitable base oils. Most importantly, avoid overusing defoaming additives. You need to monitor their quantity carefully, as excessive use can produce the opposite effect for your devices.
Material Compatibility
A qualified hydraulic fluid should be compatible with various materials, including metals, rubber, and elastomer components. Only such hydraulic fluid can adapt to diverse material environments, thereby enhancing its versatility and reducing your cost of investment.
Heat Removal
The heat removal of hydraulic fluid enables it to absorb energy from components and release it. Hydraulic fluids with poor heat dissipation cause oil temperatures to rise, which in turn increases the temperature of your system components. This can ultimately lead to system component failure.
Flow
The flow velocity of your hydraulic fluid determines how quickly pressure is transmitted throughout the system. Excessively slow flow rates reduce the operating speed of hydraulic equipment. Conversely, excessively fast flow rates cause excessive friction and wear. Meanwhile, you may find that it is simultaneously causing the generated pressure to drop.
Density
The density of hydraulic fluid affects lubrication and performance, thereby impacting the overall efficiency of the hydraulic system.
Oxidation Stability
Oxidation stability refers to a hydraulic fluid’s ability to resist chemical reactions with oxygen. If a hydraulic fluid lacks this oxidation stability capability, the chemical reaction between the fluid and oxygen will cause the hydraulic fluid to degrade or become completely ineffective.
Water Resistance
The water resistance of hydraulic oil refers to its ability to resist or repel water. Water resistance significantly impacts the performance of hydraulic oil in humid environments.
Anti-Wear
The anti-wear capability of hydraulic oil stems from the addition of the anti-wear additive zinc dithiophosphate (ZDP). It forms a protective film during operation, thereby reducing metal wear.
Corrosion Resistance
Corrosion resistance is another property of hydraulic oil. You can use additives like R&O (rust and oxidation) inhibitors to reduce the extent of system corrosion. It also protects ferrous metals from rusting.
When hydraulic oil operates at extremely high temperatures or cycles between hot and cold conditions, it becomes highly susceptible to oxidation. You might ask: What are the hazards of oxidation? Oxidized hydraulic oil corrodes softer metals like brass and bronze. It can also generate sludge, which clogs passages and prevents the system from functioning properly. You can address hydraulic oil oxidation by adding antioxidant additives.
Thermal Stability
Your hydraulic equipment operates most efficiently between 100˚F and 140˚F, with a maximum temperature not exceeding 150˚F. Temperatures above this range reduce both hydraulic fluid and system efficiency. So you need to change the hydraulic fluid more frequently.
If your hydraulic equipment operates under high-pressure conditions, we recommend premium-grade hydraulic fluid with superior thermal stability. This type of fluid resists decomposition at elevated temperatures. Avoid choosing lower-grade fluids solely for cost savings, as they conduct heat and can inflict irreparable damage to your machinery.
Conclusion
Hydraulic fluids possess a wide range of properties that combine to make them perfectly suited for your project. If you find yourself overwhelmed by the variety of options and unsure which types of hydraulic fluid to choose, feel free to consult Target Hydraulics! We’re always here to solve your challenges.
