How clean should hydraulic oil be?

We want our oil and lubricants to be as clean as possible – especially hydraulic oil. But with every machine, there comes a point where the output does not justify the cost of meeting certain cleanliness standards. 

Consequently, there is no single answer when it comes to the question of oil cleanliness. Instead, cleanliness levels and goals should be determined based on strategic maintenance: you want your oil to be clean, but you don’t want to spend extra resources on making oil cleaner than it needs to be. In determining the level of cleanliness required for your operations and to optimize cost, there are a few things to consider.

The required cleanliness level (RCL) is the target level of cleanliness established as part of a machine’s lubrication maintenance program. Oil needs to be clean, but removing every contaminant from an oil or replacing an oil every time it becomes contaminated is unrealistic, and every extra step towards cleaner hydraulic oil increases monetary costs and time expended. Some of the factors that go into determining an oil’s optimal cleanliness level are:

How delicate are the machine’s components? Certain machine components, like valves and pumps, are more sensitive to contamination. Machines with highly sensitive components will require a high level of cleanliness. Hydraulic oils and hydraulic components are often especially sensitive to contaminants like water and therefore generally require higher levels of cleanliness.

The below table can serve as a guideline for understanding how different components and pressures affect cleanliness targets. Be sure to consult your OEM and consider your particular application, including its operating temperature and environment, when setting your own cleanliness targets.

How long do you expect the machine to last? Typically measured in hours, the lifetime of a machine is heavily affected by its contamination level. If you expect a machine to remain in service for a long time, you will want to have tighter control over the contamination in that machine.

On the other hand, if you expect to replace a machine regularly you don’t have to worry as much about contamination in regards to the machine’s long-term health (contamination should however not be ignored entirely, as it can still affect the machine’s performance and productivity).

How much will it cost to replace a component? Machines with expensive or complex components typically demand higher levels of cleanliness; you don’t want to replace expensive parts more often than is necessary. Conversely, if it is cheaper to replace a component than to maintain high levels of cleanliness, cleanliness standards can be relaxed.

Will a specific machine cause significant disruption to production if laid-up? If so, then that machine should have stricter cleanliness targets. Conversely, if the failure of a machine does not disrupt production, then that machine can have looser cleanliness demands. As with low life expectancy machines, contamination should still be accounted for when considering the productivity and performance of a low-impact machine.

Does the failure of a machine present a safety risk? If so, every effort should be made, in terms of cleanliness control, to protect that machine. The last thing you want to deal with is a safety incident caused by under-serviced lubrication.

Once required cleanliness levels are set, efforts must be taken to reach these goals. Proactive maintenance strategies can be employed to reach and maintain cleanliness levels. For hydraulic systems, a good proactive maintenance program will combine elements of contaminant exclusion and contaminant removal. Contamination exclusion is often more cost-effective than contamination removal; it’s cheaper to keep contaminants out of a machine than to remove contaminants that are already inside.

Implementing a proactive lubrication program can be complex, requiring regular oil analysis, data trending, and condition monitoring. It can be difficult to move to a proactive mode of lubrication on your own, but there are many benefits that come from treating your hydraulic oil as an investment to be protected rather than a product to be consumed. Our Oil as a Service offering is designed to help clients do just that. As we have seen, cleaner hydraulic fluid can improve reliability and even extend the service life of lubricants and the machines they protect. With the power of Double Separation Technology (DST) it is possible to regenerate hydraulic oil and maintain it in a highly clean state, in some cases even indefinitely.