Most machines are compatible with several different types of lubricating oils, but in order to reach optimal machine performance, the correct oil must be selected. Going through the process of choosing the right hydraulic oil ensures that you provide your machines with what they need without wasting money on unnecessary features.
The role of hydraulic oil
The most important roles of hydraulic oil are the transfer of energy, the transfer of heat, and lubrication. Hydraulic fluids are designed with these roles in mind and have unique chemical compositions compared to other common lubricants. Generally, the makeup of a hydraulic oil is customized based on specific operational needs. The three main types of hydraulic oil are:
- Synthetic — Synthetic oils, as the name suggests, are man-made. The molecules of these oils are arranged in a way that provides high levels of fluid stability, enhanced lubricating abilities, and other performance-enhancing properties. Often, synthetic hydraulic oils are chosen for applications that involve high pressures and/or extreme temperatures. Despite their advantages, synthetic oils are typically expensive and require special handling. Additionally, such oils present the potential for compatibility issues.
- Mineral-based — Mineral-based oils are derived from crude oil and employ additives to achieve desired qualities. Common additives include viscosity index improvers, rust and oxidation inhibitors, and anti-wear agents. Mineral-based oils are a lower-cost alternative to synthetic oils and, when enhanced with the right additives, offer comparable performance.
- Water-based — Water-based oils are less common and are most frequently used in applications where there exists a high risk of fire. These oils lack wear-protection capabilities and are best suited for specific applications.
A technician examines hydraulic fluid before it is analyzed. Differences in oil type, viscosity, and additive packages can completely change the long-term performance and service life of your hydraulic assets.
Pumps and application considerations
The two most important factors when choosing a hydraulic oil are pump design and viscosity grade requirements. Every type of pump requires a different viscosity. Typically measured in centistokes (cSt), an oil’s viscosity refers to a liquid’s resistance to flowing. For reference, water is measured at 1 cSt.
Different styles of hydraulic pumps require vastly different oil viscosities. Vane pumps and Piston pumps, for instance, typically require oils with viscosities of 10 to 160 cSt. In contrast, gear pumps can operate with a wide range of viscosities, with some internal gear pumps calling for hydraulic oils with a viscosity of up to 2,200 cSt. The viscosity of an oil also needs to match the amount of pressure being generated.
Viscosity selection for Hydraulic Fluids according to pump type, operating temperature, pressure, and viscosity.
Determine a pump’s optimum viscosity requirements before selecting a lubricant. This information can be acquired through the Original Equipment Manufacturer (OEM). It is also essential to determine a hydraulic system’s operating temperature to ensure the chosen oil will function properly. Ultimately, the most important consideration when choosing a hydraulic oil is the hydraulic system’s application.
Hydraulic oil longevity
An oil’s lifespan is another important factor in the lubricant selection process, especially when considering the cost of replacing lubricants. Oils operating in dirty environments are prone to heavy contamination, which leads to more frequent lubricant changes. Certain lubricants have additives that combat some harmful effects of contamination, but even with quality additives, desiccant breathers, and quality filtration, hydraulic oil usually has a finite service life.
But today, things are changing. With the right technology and contamination control practices in place, it is possible to maintain hydraulic fluids in a “like new” state of cleanliness for much longer. In some cases, the same hydraulic oil may be used indefinitely. Consider how frequently you change hydraulic oil in your equipment. The associated environmental, labor, and product costs add up quickly. Shifting to a more proactive approach to lubrication may unlock savings and reduce the environmental impact of your operations in unexpected ways.