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Intelligent Lubrication Solutions™

Intelligent Lubrication Solutions™


Hydraulic Systems: Selecting the Right Fluid

Posted by Matt Mohelnitzky on Oct 13, 2015 8:30:00 AM


There are many different types of hydraulic equipment and machinery in use today, covering a wide variety of industries and applications. From construction to steel mills, and just about everything in-between, hydraulics enable operators to perform significant tasks (e.g., lifting heavy loads, compacting materials, metal stamping, etc.) with minimal mechanical linkage, making them ideal for high-powered jobs that would normally place a lot of stress on mechanical components. Because hydraulic fluid is nearly incompressible, it is able to transmit large amounts of power instantaneously using Pascal’s law, but given this extreme pressure, it’s important that your hydraulic fluids are a perfect match for your machinery and operating conditions.

Hydraulic fluids interact with all major components of a hydraulic system, meaning the entire system is affected by choosing the correct fluid in order to avoid unplanned breakdowns and inefficient performance. The correct fluid is dictated by your system’s operating parameters, including its environment and application—which impact the properties your fluid will need for performance. In order to achieve maximum performance and life of your hydraulic systems, you must select the right hydraulic fluid considering the system’s environment and application.

Role of Fluids in a Hydraulic System 

The way a hydraulic system works is actually quite simple. Looking at the diagram below, you’ll see that by applying force with one piston, the force is then transmitted to the second piston through the oil in the reservoir, pushing it upwards.


While the primary function of a hydraulic fluid is to transmit energy through the system, hydraulic fluids are also responsible for the important jobs of lubrication, heat transfer, and contamination removal. In order to maximize your fluid’s energy transferring capabilities and performance, it’s important that your system’s components are well lubricated, don’t overheat (or get too cold!), and that your fluid integrity meets your operating standards. Without a well-balanced fluid that can do all of those things, your equipment will suffer from decreased performance and a shortened component life.

Fluid Selection Considerations

In order to maximize your machine’s performance and lifespan, it’s important that you carefully select the perfect hydraulic fluid for your machine’s operating conditions. Hydraulic equipment will require different properties in the fluid that is used, so as to provide the proper lubricating film, heat management, oxidative and hydrolytic stability, wear protection, and environmental considerations. To help you determine the best hydraulic fluid for your specific application, here are some things to consider when choosing a hydraulic fluid.

Industrial vs. Commercial & Heavy Duty Applications

Is your machine used for industrial or commercial purposes? Depending on the application of your machine, you’ll require a certain type of hydraulic fluid:

Industrial Applications—U.S. Lubricants blends and markets THRIVE™ brand industrial lubricants for nearly every application in small and large plants. Whether it’s manufacturing, food processing, paper mills, foundry operations, or machining centers, we have what you need. Depending on the application, you have a choice of several anti-wear (AW) lubricants, such as: HP-II high performance, multi-viscosity, fire-resistant, all-season, or environmentally friendly lubricants. For a complete list of our industrial hydraulic fluid options, click here.

Commercial & Heavy Duty ApplicationsIn addition to our industrial THRIVE™ brand lubricants, we also offer THRIVE™ brand heavy-duty lubricants for everything from heavy military spec equipment to construction and logging equipment, fire trucks to concrete mixers, snow removal equipment to on-road commercial fleet vehicles, and even snow blowers and lawn tractors. Fluid categories for hydraulics include several anti-wear lubricants, such as: HP-II high performance for extreme conditions; multi-vis (for climates with extreme temperature variations); multi-vis R (extreme protection for distinct pump and system standards/specifications); zinc-free (environmentally friendly and high performance); fire-resistant; synthetic (reduces wear and ensures long oil life); synthetic all-season; readily biodegradable and renewable; and MIL SPEC (for military vehicles). For a complete list of our commercial & heavy-duty hydraulic fluid options, click here.

Operating Environment

When deciding on a hydraulic fluid for your system, make sure you consider the physical space in which your machine is located, factoring in the potential consequences of a spill and the potential for contaminants to enter into your system. Is your machine indoors or outdoors? What is the temperature of the operating environment?  What is the operating temperature of your machine? Is your machine mobile or stationary? Do you require readily biodegradable fluids? These are the types of questions you need to answer before figuring out which hydraulic fluid is best.

Machine Susceptibility

In addition to thinking about your machines operating environment, you also need to consider the failures your machine is susceptible to. For example, do you need your fluid to resist foaming? Is your machine susceptible to oxidation, rust, or corrosion? Does it require fire-resistant fluids? You can use additives to increase your antiwear protection, decrease varnish build-up, extend machine life, and lower your maintenance costs.

Fluid Properties (Viscosity Index, Wear Resistance, etc.)

When it comes to choosing a fluid for your equipment, there are several characteristics that will affect its performance:

  • ViscosityThe higher the viscosity a fluid has, the more resistance it will create compared to a fluid with a low viscosity. Likewise, higher viscosity fluids can lead to increased fluid pressure and energy consumption. If your viscosity isn’t just right, you’ll end up damaging your system.
  • Viscosity Index—Viscosity index refers to how the viscosity of a fluid changes as the temperature changes. High VI fluids will maintain their viscosity over a wider temperature range, making them more useful in applications with extreme temperatures, and particularly outdoor hydraulic systems.
  • Oxidation StabilityIncreased operating temperatures act as catalysts to oxidation, which greatly reduces the life of a fluid.
  • Wear ResistanceThe right hydraulic fluid should form a protective film on your metal surfaces to prevent abrasion and wear when coming into contact with other components. The higher the wear resistance, the better protected your machine will be.

Petroleum-based vs. Water-based vs. Synthetic Fluids

There are three common types of hydraulic fluids available on the market today, each with their own pros and cons: 

  • Petroleum-based fluids (a.k.a. mineral-based fluids) are the most commonly used fluid today, thanks to their low-cost, high quality, and ability to be modified for many different applications. Additives are often added to petroleum-based fluids to enhance their performance, with common additives including rust and oxidation inhibitors (R&O), antiwear (AW) anticorrosion agents, and defoamants.
  • Water-based fluids are pretty much exclusively used when fire resistance is needed thanks to their high-water content. When using water-based fluids, your pump, filter, plumbing, and seal materials should be checked for compatibility. Water-based fluids can also be more expensive than petroleum-based fluids.
  • Synthetic fluids (PAOs) are man-made lubricants that are ideal in high-pressure and high-temperature systems. These fluids are known for their decreased friction, natural detergency, and thermal stability, offering many benefits to operators. However, these fluids are also more expensive than petroleum-based fluids and, although typically similar in terms of compatibility, seal compatibility should be checked.

U.S. Lubricants Can Help!

Did you get all that? We know it can be quite the process. Good news is: You don’t have to do all of this analysis yourself! U.S. Lubricants can help you determine the optimum viscosity range and select a lubricant that performs efficiently at the operating parameters of the system pump and motor, as well as within the machine’s operating environment. Below is a list of the different hydraulic fluids U.S. Lubricants offers, along with their specs, suitable applications, and key features.


To learn more about how U.S. Lubricants can help your company select the optimal hydraulic fluids for your machines, please contact Tony Springer at TSpringer@uslube.com or by phone at (800) 490-4900 ext. 8823.


Topics: Hydraulic Fluids