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Como Academy

July 14, 2019

What Is Viscosity and Why Is It Important

The technical definition of viscosity when it relates to fluid is “a measure of its resistance to deformation at a given rate.”

There are two main kinds of viscosities when dealing with fluid: Dynamic viscosity, which is a measure of internal resistance to force, and Kinematic viscosity, which is a measure of internal resistance to flow when no force other than gravity is applied.

When looking at the viscosity specifications of a fluid we are typically looking at the kinematic viscosity. Centistokes (cSt) and Saybolt Universal Seconds (SUS) are the two main units of measurement used when referencing kinematic viscosity. Both cSt and SUS specifications are given at two temperatures, 40°C/100°C, or 100°F/212°F respectively. This is because viscosity will increase with higher temperatures and decrease with lower temperatures.

Monitoring Viscosity

When it comes to machine guidelines, fluid viscosity is one of the most critical aspects to monitor.

When it comes to machine guidelines, fluid viscosity is one of the most critical aspects to monitor. If the fluid viscosity falls outside of the recommended range for machine components it can no longer provide adequate lubrication to keep components protected. When the viscosity is too low it can result in a loss of oil film which will lead to excessive wear and increased mechanical friction. If the viscosity becomes too high it can result in oil oxidation, varnish build-up, and poor pumpability throughout your machine.

Monitoring the oil viscosity is also important because it can tell you if the fluid itself is within spec. Typically a fluid that is +/- 10% of its original viscosity would be considered out of spec and should be replaced. For example, if a hydraulic oil with a kinematic viscosity of 68 cSt @ 40°C (104°F) is measured for viscosity and is <62 cSt or >75 cSt @40°C (104°F) it would be considered out of spec and should be replaced.

How Does Viscosity Impact Filtration?

Viscosity plays an important role in filtration because it impacts the speed at which the fluid can be pushed through a filter to remove contaminants. As fluid viscosity increases, the flow rate that is pumped through a filter must be decreased. This is because higher viscosity fluids have a higher resistance to flow resulting in a higher pressure drop and shorter filter life. Selecting a filter with a larger micron size will help decrease the pressure drop since there will be less resistance moving through the filter.

Viscosity plays an important role in filtration because it impacts the speed at which the fluid can be pushed through a filter to remove contaminants.

At COMO Filtration we take many different factors into consideration when making a recommendation for you. Fluid viscosity and temperature are two of the main influencers in our decision-making. Extensive testing is performed at our facility using our variety of filter elements to determine proper flow rates for all fluid viscosities. We are dedicated to finding the proper equipment to ensure you get the filtration results you desire, and longest possible filter life to help maximize your investment.