What’s That: Hydraulic Fluid

Published On: March 25, 2024Categories: Daily Market News & Insights

Often overlooked yet crucial, hydraulic fluid plays a fundamental role in heavy machinery ranging from vehicle braking systems to construction equipment. Today’s What’s That Wednesday will cover the essence of hydraulic fluid, exploring its composition, the vital properties that define its efficiency, and its indispensable role in the seamless operation of hydraulic systems.


What is Hydraulic Fluid?

At its core, hydraulic fluid, also commonly referred to as hydraulic oil, is an essential component that operates as the lifeblood of hydraulic systems. These systems rely on hydraulic fluid to transmit power, ensuring the smooth operation of machinery for various applications, including those in the fuel and lubricant sectors.

Hydraulic fluids are typically non-compressible liquids, which means they retain their volume under pressure, allowing them to efficiently transfer force through the hydraulic system. Depending on the specific requirements of the machinery and environmental conditions, hydraulic fluids can be either synthetic or mineral-based.

Although the terms hydraulic fluid and hydraulic oil are often used as if they are identical, there’s a distinction between them. Hydraulic oil represents a specific category of hydraulic fluids, primarily formulated from mineral oil. On the other hand, hydraulic fluid encompasses a broader range of substances that can be utilized within hydraulic systems. Thus, while all hydraulic oils are hydraulic fluids, not all hydraulic fluids are hydraulic oils.


The Role of Hydraulic Fluid

Hydraulic fluid goes beyond merely transferring power. It serves multiple functions within a hydraulic system, acting as a lubricant to reduce friction and wear between moving parts, a coolant to manage the system’s temperature, and a sealant to prevent leaks, ensuring the system operates efficiently and effectively.


Mineral vs. Synthetic Hydraulic Oils

The distinction between mineral and synthetic hydraulic oils lies in understanding their applications and benefits. Mineral-based hydraulic oils, which constitute the majority of hydraulic oils, are refined from crude oil fractions. In contrast, synthetic hydraulic oils are engineered from chemically produced base fluids.

Synthetic oils offer several advantages over their mineral-based counterparts, including enhanced physical properties such as superior performance at high temperatures, greater biodegradability, and improved oxidation stability. These benefits make synthetic hydraulic oils a preferable choice for specific applications demanding higher performance standards.


How Do Hydraulic Systems Work?

The primary function of hydraulic oil within a system is to convey power from one part of the system to another, facilitating movement and action through various hydraulic components. This process begins when an external force, often generated by a piston within a cylinder, applies pressure to the hydraulic fluid. This pressure propels the fluid through the system, activating other components and resulting in the desired mechanical action.


A key characteristic of hydraulic fluids is their non-compressibility. While all liquids can be compressed to a certain extent, the compressibility of hydraulic fluids is so minimal that it is virtually negligible for the purposes of hydraulic systems. This property is fundamental to the efficient operation of hydraulics, as it ensures consistent power transmission and system reliability.


Hydraulic Fluid Properties

The right hydraulic fluid must possess specific properties to ensure the hydraulic system performs optimally under the designated operating conditions. This is particularly significant for industrial or commercial applications, where the demands on hydraulic systems are more rigorous.

The essential properties that make hydraulic oil effective include its non-compressibility, thermal stability across a wide range of operating temperatures, fire resistance, and non-corrosiveness to system components. Additionally, the fluid should offer anti-wear protection, have a low tendency to cavitate, and exhibit tolerance to water, including resistance to water contamination and the ability to reject water completely. Maintaining a constant viscosity regardless of temperature fluctuations, longevity, and cost-effectiveness are also key criteria. While finding a hydraulic fluid that meets all these requirements perfectly is challenging, a diverse array of hydraulic oils is formulated to excel in specific conditions, such as extreme cold or high temperatures.

The composition of hydraulic oil plays a pivotal role in its properties and effectiveness. Typically, hydraulic fluids are based on a variety of ingredients, including mineral oil, esters, glycol, silicone, ethers, and a range of other chemically complex additives. These components are blended in different proportions to create hydraulic oils with tailored properties to suit varied applications. By adjusting the mix of base oil and additives, manufacturers can produce hydraulic fluids that cater to the specific needs of different hydraulic systems, ensuring that regardless of the operational demands, there is a hydraulic fluid designed to meet the challenge effectively.


Mansfield Service Partners offers hydraulic fluids to address diverse needs ranging from food-grade water separation performance to fire-resistant uses to aviation applications, in a variety of viscosity grades with a focus on seal capability, rust, temperature, and shear stability performance. Contact one of our experts today to learn more about our extensive line of services and industrial lubricants.