Choosing the Right Hydraulic Fluid Can Pay Dividends - Whitepaper

Hydraulics have been used for thousands of years. In fact, the term “hydraulic” was coined in the 17th century. It is derived from the Greek words “hydor” (water) and aulos (pipe). Water was the first fluid used in hydraulic systems, but the corrosive effects from water led to the development of petroleum-based technologies which have continued to evolve over the years. 

While the primary purpose of the hydraulic fluid is to transmit power, it also needs to perform a variety of other jobs, as described below. Choosing a hydraulic fluid can seem confusing at times; however, making the right selection can pay dividends in the form of improved productivity and lower operating costs. 

Important Characteristics of Hydraulic Fluids:


Viscosity is the single most important characteristic when selecting a hydraulic fluid. The right viscosity improves performance throughout all components of the hydraulic system and ultimately optimizes pump efficiency, which reduces lost energy and time while lowering operating costs.

The operating temperature range plays a significant role in selecting the right viscosity. At cold temperatures, the hydraulic fluid needs to allow free equipment operation. Good cold flow equates to quicker pumpability, better mechanical efficiency and less wear. At high temperatures, the viscosity should provide adequate film thickness to mitigate pump wear and overheating.

Another important characteristic of hydraulic fluids is its viscosity index (VI), which is a measurement of an oil’s change in viscosity relative to temperature change. A fluid with a higher VI will perform better across a wider operating temperature range, providing more efficient operation during cold starts and better wear protection at higher temperatures. For that reason, multi-viscosity fluids (which tend to have higher VI’s), are more frequently recommended for equipment where operating temperatures vary. In fact, through industry studies, it has been proven that high VI, multi-viscosity fluids can save operators thousands of dollars through increased productivity and lower operating costs.

Wear Protection

Good wear protection is critical, especially to protect the hydraulic pump. Anti-wear hydraulic fluids are most common and are typically formulated with a zinc-containing additive designed to coat surfaces for metal-to-metal protection. There are also applications that may recommend a “zinc-free” formulation. These oils are environmentally friendly.

Water Handling Capabilities

Hydraulic systems are typically open to the atmosphere, so humidity is common. In most industrial hydraulic systems, operators can drain off excess water, so demulsibility characteristics are very important. Demulsibility refers to a fluid’s ability to separate out water for easy removal.

In some mobile applications, it is not common or easy to drain excess water, so there are hydraulic fluids formulated to emulsify water, meaning the water is encapsulated and held in suspension. This prevents water from coming into contact with metal surfaces, which prevents corrosion, rust and filter plugging.

Foam Suppression

Foam causes spongy hydraulics, leading to loss of performance. Foam is also detrimental to hydraulic pumps and can decrease lubricant life, so good foam suppression is very important when selecting a hydraulic fluid.

Oxidation Resistance

It is quite common for hydraulic systems to operate at higher temperatures. Heat accelerates oxidation, leading to thicker oil, deposit build-up, varnish and sludge. Hydraulic oils with good oxidation resistance will not only last longer than sub-par fluids but will prevent the negative effects of oxidation, including varnish build-up on valves.

Archer-Quality Worth Talking About

The Archer line-up of hydraulic oils includes fluids with extremely low pour points for colder climates and fluids with superior anti-wear properties and outstanding thermal stability. These hydraulic fluids provide excellent protection from rust, oxidation, foaming, and wear while increasing performance and productivity.

Contact your local Archer distributor for more information or visit www.ArcherOil.com.