Hydraulic fluid contamination can cause major damage to hydraulic fluid power systems. To keep hydraulic fluid clean, it is important to know the main sources of contamination. In this article, we look at 5 major sources of contamination in hydraulic systems, followed by recommendations for how to address or prevent each.

Source #1: Hydraulic Fluid Contamination During Production

Facilities that produce hydraulic fluid may accidentally introduce contamination during processing and put contaminated fluid out on the market.

Since contamination can happen right out of the gate, it’s possible that a new batch of fluid was bad from the start. If the producer does not have (or adhere to) rigorous quality standards for manufacturing, or they simply experienced a production issue they’re not aware of that introduced a contaminant into the fluid, it will result in higher-than-acceptable levels of contamination.

Recommendation: Filter All Fluids

Filtration is an underprioritized part of a hydraulic system’s design, even with the amount of damage it can prevent by reducing contamination. Given how common contamination is, it is important to put a focus on hydraulic fluid filtration if you want your system to operate consistently & efficiently.

Source #2: Improperly Sealed Containers & Contamination During Storage

A sealed container of fresh hydraulic fluid is still at risk for contamination while it is being stored. One contamination-causing danger to sealed containers is moisture – it can seep into sealed containers in an effect known as breathing.

Breathing results in an accumulation of moisture in the storage container. It takes place when a container is improperly stored, for instance if the storage location caused the container’s temperature to go up and down—such as if it were stored outside in the sun during the day.

Unlike a car windshield experiencing the effects of condensation, it is not common to see the effects of moisture contamination in hydraulic fluid. It can be extremely damaging to a hydraulic system and its performance so it’s important to have a plan to mitigate it.

Loosely sealed containers—or those left open—create another source of contamination. In this case, in addition to moisture, dust and debris can easily enter the container due to the poor seal.

Recommendation: Control Temperature and Properly Seal Containers

The best way to prevent storage-related moisture contamination is to store fluids at a controlled temperature out of direct sunlight. To mitigate the contamination resulting from poorly-sealed containers, lay hydraulic fluid containers on their sides. Make sure to carefully – and completely—seal fluid that is not in use. Inspect container seals carefully upon receipt as another preventative measure.

Still worried about moisture contamination? Consider whether a desiccant breather would be useful to your hydraulic system.

Source #3: Contamination During Fluid Transfer

Fluids exposed to the atmosphere during transfer and handling risk absorbing moisture due to the effects of fluctuating temperatures on the container. They also have an increased risk of being exposed to dust and other particles in the air.

If the environment where the transfer is taking place is not clean, and the equipment used is dirty, the contamination risk is high.

Finally, flushing a hydraulic system is an important final step in the transfer of fresh fluid. Failure to flush the system before adding the new fluid creates a perfect scenario for contamination.

Recommendation: Follow a Strict Fluid Transfer Process

Minimize the chances of contamination by following these steps:

  • Do not open the fluid in an area that is not clean;
  • Do not leave the lid off the fluid longer than necessary;
  • Always flush the system before adding fresh fluid;
  • Always filter all hydraulic fluid before adding it to the system.

Source #4: Built-In Hydraulic Fluid Contamination

It is possible that a cause of contamination was inadvertently built into a hydraulic system during the manufacturing process, or is a byproduct of another machine defect.

Perhaps there is a tiny remnant of Teflon sealing tape on a hydraulic port. There may also be grease or other lubricants that were not completely wiped off as the pump was assembled. Any of these situations can cause fluid contamination. Unfortunately, not all of the causes can be fixed.

Recommendation: Filter, Filter, Filter

Address built-in contamination by appropriately and regularly using filters, which includes selecting the appropriate hydraulic filter media for your application, changing filters on a regular schedule and careful handling of the filters when they are installed.

Source #5: Fluid Contamination During Service

During service, a number of factors can lead to hydraulic fluid contamination, including:

  • Exposure to high temperatures;
  • The degrading of hydraulic fluid over time;
  • Moisture and debris from old, failing seals;
  • Tiny, loose pieces of bearings and other components.

Recommendation: Flush, Fill & Replace

When you suspect the fluid has begun to degrade or it has been exposed to high temperatures, the system should be flushed and new, filtered hydraulic fluid should be added.

Replace seals as suggested by the manufacturer, or whenever a leak is suspected, and regularly replace filter media.

Careful Handling & Regular Maintenance Keep Hydraulic Fluid Clean

There are many circumstances during which hydraulic fluid contamination can occur and damage a hydraulic fluid system. Careful attention to fluid cleanliness during various phases and functions will go a long way toward reducing contamination.

It is also key to keep up a regular maintenance schedule regarding system flushes, filter changes and seal soundness.

Steve Downey
Steve Downey

Steve Downey is an Adjunct Fluid Power Instructor at Henry Ford Community College and Macomb Community College. He has worked in the Fluid Power Industry for 30 years in both Industrial and Mobile Hydraulics. Steve Holds 11 International Fluid Power Society certifications.