Three Questions to Ask Before Choosing Hydraulic Fluid

Lubrication. Anti-wear. Heat transfer. Sealing. Pump efficiency. Hydraulic fluid wears many hats, but that doesn’t mean that they are one–size–fits–all. When choosing the proper hydraulic fluid, the requirements are based on many factors including the fluid’s components and the hydraulic system itself. With that, here are three questions you should be asking yourself before choosing a hydraulic fluid.

What are the Characteristics of My Hydraulic System?

The type of hydraulic fluid that you need is dependent upon the type of hydraulic system you operate: vane, gear, or piston pumps. Unlike piston pumps, which run along an oil film, vane and gear pumps involve metal-to-metal contact. Due to this, they require a fluid with strong anti-wear (AW) capabilities over rust and oxidation (R&O) capabilities. That said, if your operation takes place in an environment where humidity is present, R&O capabilities may be just as important. Paying attention to the additives and components of the hydraulic fluid can make a great difference in fulfilling these needs. 

Furthermore, take into consideration the following:

  • System speed
  • System operating temperature
  • System’s age
  • Load size

Are My Options Limited?

The answer to this question lies in the base stock. Is a common mineral oil-based fluid sufficient for your pump? Or, is there a possible fire hazard that makes a petroleum or mineral oil-based fluid dangerous at high operating temperatures? In this case, a flame-retardant hydraulic fluid would be best. This may include a water-glycol or ester-based fluid.

Or, perhaps a biodegradable hydraulic fluid is more aligned with your environmentally-conscious operation. Hydraulic fluids that use rapeseed (canola) oil have a lesser impact on the environment, best for a setting with strong environmental restrictions.

What is The Most Effective Viscosity Index for My Operation?

Remember the first question? This is where your system’s characteristics make all the difference. Start with your system’s operating temperature. Typical ISO viscosity grades include ISO 32, 46, 68, and 100 or above for particularly heavy-duty fluids. As these numbers increase, the fluid’s ability to maintain its viscosity at higher operating temperatures increases as well. Therefore, a high operating temperature may require a grade of 68 or higher. Consider, however, if a very thick lubricant is fluid enough for your system’s speed. Try out our line of Truegard products for just about any operation:


Rust and oxidation:

Don’t forget to also look at the system’s age and condition. Does your system run the same as it did five years ago? Is a certain viscosity still appropriate? Is there any contamination that may compromise viscosity, or that first requires maintenance? Your system may be more nuanced than what it would theoretically be in a new model, so it is important to choose hydraulic fluids on a case-by-case basis.


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