For operators looking to maximize productivity and reduce downtime in hydraulic applications, the correct specification of hydraulic oil is vital. Research from Shell Lubricants companies, which have been producing hydraulic oils for more than 50 years, shows that 70 percent of hydraulic equipment problems are due to the improper condition of hydraulic oils.

Although some of this is due to the performance of the oil in operation, companies need to play their part by selecting the most appropriate hydraulic oil in the first place.

The first thing operators should check is the OEM manual and specific lubrication guidelines and/or standards that are appropriate to their hydraulic system and production specifications.

A crucial and costly part of a hydraulic system is the pump, and engineers need to check the maximum oil viscosity (thickness) at which it will start and the minimum at which it will run while taking into consideration seasonal influences.

System risks

If the thickness of the oil selected is too high, money is being wasted because extra energy is needed to pump the fluid around the system.

During the winter period, problems associated with the selection of too high viscosity oils are exacerbated.

In extreme cases, if the viscosity is significantly higher than specified, severe damage to the pump and system may occur due to "lubricant starvation" – where the pump fails to deliver the fluid around the system.

Other risks include cavitation and possible filter damage, especially in open loop hydraulic systems common in mobile hydraulic equipment, which can all result in costly downtime.

In addition, equipment filled with a higher viscosity oil can take longer to reach operating temperature from startup, possibly requiring the use of additional reservoir heating to thin the oil to the correct viscosity, potentially wasting vital production time.

Take Note

If the oil viscosity is too low, an insufficient lubrication film is formed between moving parts, resulting in accelerated wear.

This is most likely to occur in highly loaded contact areas and could result in catastrophic failure or a long-term decline in system performance.

Increased wear also can result in larger clearances than originally designed, resulting in increased leakage and system noise during operation.

"Checking the OEM guidelines is a must in order to determine the correct viscosity of a hydraulic oil for use in a specific application," said Eduardo Tavcar, product manager for Shell Lubricants' Global Hydraulic Oils. "However, operators looking to optimize performance should look further than just OEM requirements. They should check all of the characteristics of a lubricant. Leading lubricant manufacturers have developed hydraulic oils which surpass these guidelines in order to extend areas such as oil life."

Consider temperature

Once the correct viscosity oil has been selected, a factor that many operators fail to consider is the actual surrounding temperatures in which a machine will operate.

Machines and applications that are regularly exposed to the outside environment (such as lifts and cranes, off-road hydraulic equipment and high-precision presses) are open to wide variations in operating temperatures depending on factors such as location, season and startup versus operating temperature.

These can all have a significant effect on the viscosity of the hydraulic oil and its lubrication properties.

For mobile and stationary hydraulic applications regularly exposed to the outside environment, operators need to ensure that they select an oil that has a wide operating temperature range and can adapt to an increase or decrease in temperature to ensure minimal viscosity change.

A good way to estimate any change in temperature is to check local weather reports over the past 12 months, taking into account any summer/winter temperature highs and lows. A lot of this information is freely available on the Internet.

"It's all a matter of careful selection," Tavcar said. "Understanding the full range of temperatures to which a hydraulic oil will be exposed is key to selecting an oil to optimize performance."

Once the temperature range has been calculated, engineers can then look to match it against the most appropriate oil.

In choosing a variable temperature hydraulic oil, operators should ensure the fluid has a high shear stability (the polymers' resistance to stress, which can break the molecules and reduce the viscosity of an oil at operating temperature), as well as excellent hydrolytic stability, which reduces the impact of unavoidable water condensation in machinery after shutdown, helping to reduce wear and corrosion.

"The true test of a good variable temperature hydraulic oil is finding one which offers a wide temperature range as well as other key performance features such as excellent shear and hydrolytic stability," Tavcar said. "Only by choosing a product that performs well in all areas will you be able to reduce downtime and maximize productivity."