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Why Are Hydraulic Fluids Important and How Do You Choose the Right One?

Why Are Hydraulic Fluids Important and How Do You Choose the Right One?

Hydraulic systems are the backbone of numerous industries, providing the power necessary for heavy machinery, industrial applications, and even renewable energy projects. At the heart of these systems lies the hydraulic fluid, a crucial component that ensures efficient operation, longevity, and safety.

In this post, we'll explore why hydraulic fluids are essential and guide you through choosing the right one for your system. We'll discuss the different types of hydraulic fluids, their properties, and key selection criteria to help you make an informed decision.

The Importance of Hydraulic Fluids

Hydraulic fluids perform several critical functions in a hydraulic system:

Power Transmission

Hydraulic fluids transmit power from the hydraulic pump through valves to actuators or motors. The fluid's ability to flow and transmit force from one location to another through pipes or flexible hoses is essential for efficient system performance.

An image of an old excavator with a red and black structure, equipped with steel cables (strings) instead of a hydraulic system. The excavator is positioned outdoors on gravel, with trees and a blue sky in the background.

Lubrication

Oil is now widely used because it freezes at much lower temperatures, turns to gas at much higher temperatures, and is a much better lubricant of a system's components. Oil reduces friction and wear, helping to reduce maintenance costs and extend the life of your equipment.

Close-up image of a shiny hydraulic system with multiple cylinders and pipes, lubricated with oil. The system features yellow and black components, with visible connections and fittings, highlighting the complexity and precision involved in hydraulic machinery. The shine indicates the effectiveness of oil in reducing friction and wear.

Heat Dissipation

Hydraulic systems generate heat during work operations. Hydraulic fluids absorb and dissipate this heat, preventing overheating and ensuring the system operates within safe temperature ranges. If temperatures in a hydraulic system are too high, several detrimental effects can occur. The hydraulic fluid can degrade, losing its lubricating properties and leading to increased friction and wear on components. This degradation also reduces the fluid's viscosity, impairing its ability to transmit power efficiently. High temperatures can cause seals and hoses to harden and crack, resulting in leaks and reduced system pressure. Additionally, metal components may expand, leading to tighter tolerances and potential binding or seizure of moving parts. Overall, excessive heat can significantly reduce the efficiency, reliability, and lifespan of a hydraulic system.

Close-up image of a hydraulic cylinder showing signs of heat damage and wear. The surface is corroded and the surrounding area appears degraded, illustrating the detrimental effects of high temperatures on hydraulic components. This visual highlights the importance of hydraulic fluids in absorbing and dissipating heat to prevent overheating and maintain system efficiency.
Close-up image of a hydraulic cylinder with visible oil leakage. The seal area shows signs of wear and degradation, illustrating the impact of high temperatures on hydraulic components. This visual emphasizes the importance of hydraulic fluids in absorbing and dissipating heat to prevent overheating and ensure the system operates efficiently and reliably.
Close-up image of a hydraulic hose showing significant cracking and wear. The surface of the hose is deteriorated, demonstrating the effects of high temperatures on hydraulic system components. This visual highlights the critical role of hydraulic fluids in absorbing and dissipating heat to prevent overheating, which can cause hoses to harden, crack, and ultimately fail.

Corrosion Protection

Quality hydraulic fluids contain additives that protect the system's components from rust and corrosion, especially in harsh environments.

Close-up image of two rusted and corroded threaded metal components. The severe rusting highlights the importance of using quality hydraulic fluids with additives that protect system components from rust and corrosion, particularly in harsh environment

Contaminant Removal

Hydraulic fluids help transport contaminants to the system's filters, maintaining cleanliness and preventing damage to sensitive components. Contaminants in hydraulic systems can significantly damage sensitive components through various mechanisms. Abrasive particles can scratch and wear surfaces of pumps and motors, reducing efficiency and causing failures. Contaminants can clog valves and orifices, resulting in erratic behavior. Substances like water cause corrosion in cylinders and pumps, weakening structural integrity. Fluid degradation from contaminants can form sludge that affects seals and gaskets, leading to leaks. Erosion from particles can alter the dimensions of precision components like pumps, motors, and servo valves. Hard particles cause galling in piston rods and bearings. Increased friction generates excessive heat, degrading components and fluid. Finally, contaminants can interfere with electrical sensors and actuators, causing erroneous readings and malfunctions. Effective filtration is essential for the longevity and reliability of hydraulic systems.

Close-up image of a hydraulic system filter with a cylindrical design, surrounded by pipes and fittings. The filter is clean and well-maintained, illustrating the role of hydraulic fluids in transporting contaminants to filters, ensuring system cleanliness, and preventing damage to sensitive components.

Types of Hydraulic Fluids

Selecting the right hydraulic fluid depends on understanding the different types available and their specific properties. Here are the most common types:

Mineral Oil-Based Fluids

Mineral oil-based fluids are the most widely used hydraulic fluids. They are derived from refined petroleum and are known for their excellent lubricating properties and thermal stability. These fluids are suitable for a wide range of applications, including industrial machinery, automotive systems, and construction equipment.

Close-up image of a bright yellow hydraulic cylinder with a polished steel rod. The clean and well-maintained appearance highlights the use of mineral oil-based hydraulic fluids, known for their excellent lubricating properties and thermal stability, suitable for industrial machinery, automotive systems, and construction equipment.

Synthetic Fluids

Synthetic hydraulic fluids are engineered from chemical compounds to provide superior performance in extreme conditions. They offer better thermal stability, oxidation resistance, and low-temperature fluidity compared to mineral oil-based fluids. Synthetic fluids are ideal for applications requiring high-performance lubrication and extended fluid life, such as aerospace, military, and advanced manufacturing.

Image of an aircraft hangar with a fighter jet undergoing maintenance. Technicians are working with advanced hydraulic equipment, highlighting the use of synthetic hydraulic fluids. These fluids are engineered for superior performance in extreme conditions, offering better thermal stability, oxidation resistance, and low-temperature fluidity, making them ideal for aerospace, military, and advanced manufacturing applications.

Water-Based Fluids

Water-based hydraulic fluids include water-glycol solutions and water-oil emulsions. These fluids are non-flammable, making them suitable for use in fire-prone environments like steel mills and foundries. However, they have lower lubricating properties and require more frequent maintenance to prevent corrosion and bacterial growth.

Image of a steel mill with large industrial machinery and glowing hot metal being processed. The environment showcases the use of water-based hydraulic fluids, such as water-glycol solutions and water-oil emulsions, which are non-flammable and ideal for fire-prone settings. These fluids require more frequent maintenance to address their lower lubricating properties and prevent corrosion and bacterial growth.

Biodegradable Fluids

Biodegradable hydraulic fluids are designed to minimize environmental impact. They are typically made from vegetable oils or synthetic esters and degrade naturally over time. These fluids are ideal for use in environmentally sensitive areas, such as forestry, agriculture, and marine applications. Biodegradable fluids provide good lubrication and thermal properties but may have shorter service lives compared to synthetic fluids.

Image of a green logging machine in a forest, lifting logs with its hydraulic arm. This scene illustrates the use of biodegradable hydraulic fluids, made from vegetable oils or synthetic esters, which minimise environmental impact. These fluids are ideal for forestry, agriculture, and marine applications, providing good lubrication and thermal properties while being environmentally friendly

Properties of Hydraulic Fluids

When choosing a hydraulic fluid, it's essential to consider its properties to ensure it meets the specific requirements of your application. Here are some key properties to evaluate:

Viscosity

Viscosity is a measure of a fluid's resistance to flow. It affects the fluid's ability to transmit power and lubricate components. Hydraulic fluids should have a viscosity that matches the operating conditions of the system. Low viscosity such as ISO 32 can lead to increased wear and reduced efficiency, while high viscosity such as ISO 120 can cause excessive friction, heat generation, and in some cases cavitation.

Chart titled "Viscosities of Various Liquids" showing approximate values at 20-24°C. The chart categorizes liquids into low viscosity (1-1,000 mPa·s), medium viscosity (1,000-100,000 mPa·s), and high viscosity (100,000-1,000,000 mPa·s). Examples include water, salad oil, and engine oil in the low viscosity range; mayonnaise, honey, and chocolate in the medium range; and peanut butter, silicone sealant, and shortening/lard in the high viscosity range. This illustrates how viscosity affects a fluid's ability to flow, transmit power, and lubricate components in hydraulic systems.

Viscosity Index (VI)

The viscosity index indicates how much a fluid's viscosity changes with temperature. A high VI means the fluid maintains a more consistent viscosity across a wide temperature range, ensuring reliable performance in varying conditions.

Graph showing the viscosity-temperature relationship for crude oil, a commingled mixture (3:1), and GTL (Gas-to-Liquids) fluid. The x-axis represents temperature (°C) ranging from -30 to 70, and the y-axis represents viscosity (kg/m·s). The graph illustrates how viscosity decreases with increasing temperature for each fluid. This highlights the importance of the viscosity index (VI), which indicates how much a fluid's viscosity changes with temperature, with a high VI ensuring consistent performance across a wide temperature range.

Thermal Stability

Thermal stability refers to a fluid's ability to resist degradation at high temperatures. Hydraulic fluids with good thermal stability maintain their properties and performance under heavy load and high-temperature conditions, reducing the need for frequent fluid changes.

Image of a large industrial machine in a factory setting, highlighting the importance of hydraulic fluids with good thermal stability. The machine's size and complexity illustrate the need for fluids that can resist degradation at high temperatures, maintaining performance under heavy load and high-temperature conditions, thereby reducing the frequency of fluid changes.

Oxidation Resistance

Oxidation resistance is the fluid's ability to resist chemical breakdown due to exposure to oxygen. Fluids with high oxidation resistance have longer service lives and provide better protection against sludge and varnish formation.

Lubricity

Lubricity is the fluid's ability to reduce friction between moving parts. Hydraulic fluids with excellent lubricity minimize wear and extend the life of system components.

Close-up image of various hydraulic components and fittings, illustrating the importance of lubricity in hydraulic fluids. The metallic parts highlight the need for fluids that can reduce friction between moving parts, thereby minimizing wear and extending the life of system components.

Corrosion Protection

Corrosion protection is essential to prevent rust and corrosion in hydraulic systems. Quality hydraulic fluids contain additives that form protective films on metal surfaces, safeguarding against moisture and contaminants.

Water Tolerance

Water contamination is a common issue in hydraulic systems. Fluids with good water tolerance can separate and remove water, preventing emulsification and maintaining system performance.

Selection Criteria for Hydraulic Fluids

Choosing the right hydraulic fluid involves evaluating the specific needs of your system and operating environment. Here are some critical criteria to consider:

Operating Temperature

Consider the temperature range in which your system operates. Ensure the hydraulic fluid has a suitable viscosity and viscosity index to perform reliably across this range.

Load and Pressure

Evaluate the load and pressure conditions of your hydraulic system. Select a fluid with the appropriate lubricity and thermal stability to handle these conditions effectively and always follow manufacturers' specifications whenever possible.

Environmental Impact

If your system operates in environmentally sensitive areas, consider using biodegradable hydraulic fluids. These fluids minimize environmental harm in case of leaks or spills.

Image of a construction excavator operating near a waterway, illustrating the importance of using biodegradable hydraulic fluids in environmentally sensitive areas. The setting emphasizes the need for fluids that minimize environmental harm in case of leaks or spills.

Fire Risk

In fire-prone environments, opt for water-based hydraulic fluids. Their non-flammable properties enhance safety and reduce the risk of fire hazards.

Compatibility

Ensure the hydraulic fluid is compatible with your system's materials and seals. Incompatible fluids can cause swelling, cracking, and other damage to seals and components.

Manufacturer Recommendations

Always refer to the equipment manufacturer's recommendations when selecting hydraulic fluids. Using recommended fluids ensures optimal performance and maintains warranty coverage.

Hydraulic fluids are vital for the efficient and reliable operation of hydraulic systems. Understanding the different types of hydraulic fluids, their properties, and key selection criteria is essential for choosing the right fluid for your application. By considering factors such as operating temperature, load, environmental impact, and manufacturer recommendations, you can ensure your hydraulic system performs at its best, minimizing downtime and maintenance costs. Whether you’re operating industrial machinery, construction equipment, or renewable energy systems, selecting the right hydraulic fluid is a critical step towards achieving operational excellence.

Next article How Hydraulic Reusable Fittings (Field Fittings) are changing the game.

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