Hydraulic Efficiency: Impact of Temperature and Fluid Viscosity

Like looking for the Philosopher’s Stone in the Middle Ages or the Fountain of Youth in the 1600s, owners and operators of large machinery are always looking for better hydraulic efficiency for their hydraulic pumps and motors. Besides the obvious need to protect the moving parts in their machines via strong hydraulic fluids, there’s also the increased operational efficiencies to consider as well as the fewer repairs that come along with a maximized hydraulic fluids system. And of course there are many theories about the best way to go about getting this ultimate hydraulic efficiency.

A recent article on Machinery Lubrication.com explains that the real way to solve the hydraulic efficiency equation is by balancing the viscosity and the temperature of the hydraulic system for best results. As the article reports:

“Hydraulic efficiency in terms of hydraulic fluid depends on a few factors, all of which relate to the viscosity of the hydraulic fluid. Low viscosity, either from poor fluid selection or high temperatures, results in a loss of volumetric efficiency, overheating and wear. High viscosity, either from poor fluid selection or low temperatures, results in poor mechanical efficiency, difficulty starting up and wear.

Hydraulic pump and motor manufacturers have often based hydraulic fluid recommendations on viscosity requirements at startup, optimum running states and extreme running states. With this being the case, temperature control and/or controlling the fluid viscosity fluctuations will be critical in managing the two main drivers of hydraulic pumping efficiency.”

Since many machines utilizing hydraulic fluid systems tend to be stationary machines in controlled environments, controlling the temperature of the external environment is the easy part of the equation, and most hydraulic fluid manufacturers even provide information regarding the optimum temperature at which their fluids will operate at peak levels.

Selecting the hydraulic fluids themselves can prove a tougher problem – every manufacturer will claim that their product is the best, but we all know that isn’t the case. Some machinery manufacturers will recommend a certain brand of hydraulic fluid for their devices – this can be due to cross-promotions between the fluid and machinery manufacturers or some other partnership deal, or because the machine producer truly knows that there’s a great brand of fluid in the marketplace that works best for their machinery. If your machinery equipment manufacturer has a recommendation, we suggest you go with it.

Otherwise, as the article notes, a multigrade hydraulic fluid may be the best option since it can cover many scenarios. As the article explains, “When a hydraulic system is required to perform at temperature extremes, it is almost certain that a multigrade hydraulic fluid will be necessary to provide the highest efficiency.”

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