What Is Hydraulic Fluid for and Why Is It Important

For any hydraulic system, fluids are the most critical component! 

hydraulic fluid running in a hydraulic machine

For fluid power applications, the primary distinguishing element is that fluids are present, which is the case with hydraulics and pneumatics. Hydraulic fluid is also required for each operation in a hydraulic system.

To move energy from one area of the system to another, hydraulic systems require incompressible hydraulic fluids, often known as hydraulic oils or liquids. Fluids are kept in a reservoir and are sucked up by a pump that moves them through the pipes to other components during hydraulic system operation.

Continue reading this article to know what hydraulic fluid is for.

Characteristics of a Great Hydraulic Fluid

1. Viscosity

The viscosity of hydraulic fluid measures flows resistance. It is the essential property of hydraulic fluid and substantially impacts the system’s performance.

Sealing is compromised when the hydraulic oil is too thin or viscous. As a result, there is a risk of leaks and part wear. Viscosity in hydraulic oil refers to how difficult it is to pump through the system, which can hurt performance.

2. Compressibility

Compressibility indicates how much volume is reduced when subjected to stress. A slight volume loss can occur even though hydraulic oils are essentially incompressible.

3. Resistance to Deterioration

Hydraulic fluid can minimize the rate at which it wears out in frictional boundary contact. Metal surfaces can be shielded against abrasion, scuffing, and contact fatigue with the antiwear components found in antiwear hydraulic fluids. Improved lubricant performance and longer equipment life can be achieved by using antiwear additives.

4. Stability of Oxidation

Heat-induced deterioration is caused by chemical reactions between oxygen and hydraulic oil. Additives that prevent oxidation, increase the fluid’s stability, and extend its life are required in hydraulic oils. You should expect the hydraulic oil to lose its quality rapidly if you don’t use these additions.

5. Stability in the heat

Thermal stability refers to a material’s capacity to withstand high temperatures without breaking down. At increasing temperatures, the degradation of antiwear additives is accelerated. Sludge and varnish can clog filters, reduce flow, and lengthen downtime due to low-temperature stability.

6. Filterability

Hydraulic fluid additives can react with water to produce an oil-insoluble substance. These impurities can precipitate from the lubricant and obstruct the flow of oil or cause the system to be bypassed. Unanticipated downtime is a possibility if a blockage persists. Filtration of hydraulic fluids in modern systems poses no threat to the additive because of the design of the fluids.

7. Anti-corrosion and Rust Prevention

Water can interact with hydraulic oil in many systems by condensation or contamination. Hydraulic components might corrode if they come into contact with water. As a bonus, some additives can react with water to generate chemical species that can harm yellow metals when combined. In hydraulic oil compositions, corrosion and rust inhibitors prevent water and other chemical species from interacting with the metal surfaces.

8. The Resilience of the Foam

When air or other gases are entrained into the hydraulic fluid, it Foam. The reservoir or air leaks inside the hydraulic system are the two main entry points for air into the system.

Large amounts of dissolved or distributed air bubbles can be found in hydraulic fluids under high pressure. Depressurization causes bubbles to expand and create Foam. Foam can significantly impact machinery performance and lubrication due to its compressibility and poor lubricating characteristics. Because they reduce air bubble surface tension, suitable foam inhibitors help break up Foam faster.

9. Demulsibility

Hydraulic oil can emulsify or combine with water that enters the system. Using this ‘wet’ fluid might lead to corrosion and rust if circulated through the system. Mineral oils that have been significantly refined allow water to separate or demulsify more easily. Hydraulic oils, on the other hand, often contain additives that cause emulsion formation, preventing water from dissolving and settling out of the fluid.


Top 5 Importance of Hydraulic Fluid

Hydraulic oils have a significant impact on the system’s productivity. Hydraulic systems are often made for high-speed, high-pressure, and high-temperature applications. Premature system failure can be avoided by analyzing and adequately maintaining the oil.

The task at hand determines the type of hydraulic fluid used. The perfect hydraulic fluid has a few characteristics. For example, lubrication and deductibility (the ability to release water), chemical and environmental stability; fire resistance; low flammability; foam resistance; low volatility, etc., are all included. 

1. Power Generation

The principle of Pascal’s triangle underlies the operation of every hydraulic system. For a process to be completed, an incompressible fluid must be present in the system that can transmit energy from one location to another. At the point of limitation, pressure builds up as a result of the flow being initiated by the pump. Force multiplication and control in any direction are also options.

2. Remove Contaminants

To avoid damaging the system or decreasing productivity, remove any pollutants that may be present. Solid particles or water can be used as pollutants. Hydraulic fluids play a critical role in the removal of these system pollutants. All of the foreign matter is carried by the fluid to the filter.

3. Lubrication and Protection

To prevent premature failures and wear, proper lubrication must be applied. There is much friction if the parts of the hydraulic components (pumps, motors, valves, etc.) are constantly moving. By forming a lubricating coating between the moving parts, hydraulic fluids can minimize friction.

4. Sealing

Most hydraulic systems include seals to prevent leaks and foreign particles from entering the system. Nonetheless, hydraulic components, such as control valves, will operate in highly compact spaces. The hydraulic fluids between mechanical parts will also serve as sealants.

5. Heat Transfer

Overheating is caused by friction between moving parts and the metal surface. Radiant cooling is provided by circulating fluid.



Many mobile and stationary machinery run on hydraulic fluid. It’s impossible to overstate the importance of protecting this valuable medium. While a quality fluid has been built and designed to execute complex duties, it cannot make up for a system with a small reservoir or a motor with a high shaft load, which must also be considered. In a well-designed hydraulic system, the good quality hydraulic fluid serves the vital function of connecting the pump and actuator and any components in between.