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Be on the Watch for These Six Types of Hydraulic Fluid Contamination

Hydraulic system contamination is a problem that affects all hydraulic equipment types. In this article, we take a close look at the six most common types of hydraulic fluid contamination: built-in, generated, water, chemical, air, and ingressed particulate (the technical way of saying dust and droplets). How does this contamination get into your system in the first place? What does it do once it’s there? And what can you do to help avoid or limit the damage?

Types of Hydraulic Fluid Contamination:
1. Built-in Contamination

Of all the types of hydraulic fluid contamination, this is the least avoidable. Despite the best efforts of most OE manufacturers, all new equipment comes with some level of built-in contamination. Components, such as final drive motors or pumps, will have residual contamination from the manufacturing process. Machinery built from those components will add to the overall contamination, with additional found from its own assembly. No matter how controlled the manufacturing environment is, it’s inevitable for one or more of the following to make it through to the final product:

Piston rings are severely damaged by contaminants
  • Metal shavings left by drilling/tapping/grinding and threading metal components together 
  • Fine granules from component finishing processes 
  • Weld spatter from component manufacturing and solidified flux from fittings and pipe soldering 
  • Thread/fiber from cloth and paper used to clean components before installation 
  • Excessive grease/lubricant used in the assembly

If any of these surface contaminants on your equipment make it through to your hydraulic fluid, they contribute to contamination, which can impact your machinery’s efficiency.

Industry experts recommend that every time you install new hydraulic components to flush your hydraulic system to address this built-in contamination. The same recommendation applies whenever machinery is overhauled. In addition to flushing, the best approach to address built-in hydraulic fluid contamination is to ensure you’re using the best quality filters. Donaldson’s filter range covers every application, with options to suit different fluid characteristics and efficiency requirements.

2. Generated Contamination

During operation, moving components wear on each other and fine, dust-like metal particles are worn away from surfaces and joints. This is especially problematic when there’s insufficient lubrication, due to the wrong choice of fluid or a leak. The problem often occurs during the initial equipment break-in phase: either when commissioning a full new system or restarting an existing system with new components. This abrasion results in generated hydraulic fluid contamination.

Generated hydraulic fluid contamination isn’t always metal dust and fragments: particles from degraded rubber or polymer seals also break away over time. Occasionally, a larger particle will break off – for example, a chip that cracks off a gear cog, or a splinter from a metal edge.

Generated types of hydraulic contamination build up as your equipment runs and can negatively impact the efficiency of its hydraulic components. Worse yet: what starts as limited localized generated contamination can have an indirect effect, producing additional wear-and-tear as these contaminants disperse throughout the entire system.

Generated hydraulic fluid contamination is inevitable in any operating equipment, but using the right filters, and changing them regularly, will limit the potential damage.

3. Air Contamination

Foaming is typically the result of air contamination in hydraulic oil. Air in your hydraulic fluid affects its compressibility. Depending on the degree of the contamination, it may affect your machinery’s efficiency: cycle times may be impacted, or the torque from your final drive could be reduced.

To minimize air contamination in hydraulic oil, protect your hydraulic system from atmospheric exposure. Keep the system sealed aside from when performing essential inspections or maintenance. Never leave hydraulic fluid exposed when it’s in storage – make sure that containers are airtight and stowed where they won’t be damaged or pierced.

4. Water Contamination

Water is all around us and the humidity of the air can be a large source of contamination of hydraulic fluids. Air humidity varies depending on location and may be seasonal, so it’s worth keeping track of variations in environmental conditions around your hydraulic equipment. If you ever notice your hydraulic fluid is looking milky, this is a strong indicator of water contamination.

As with air contamination, water contamination in hydraulic oil affects compressibility and efficiency. Water contamination in hydraulic oil also reduces the lubricity of hydraulic fluid and may lead to sludge in your system. Possibly of greatest concern, though, is that water contamination can give rise to oxidization and corrosion with irreversible effects. Surface fatigue and cavitation on metal surfaces may lead to expensive and time-consuming repairs and replacements, depending on the location and severity of the damage.

While some choose to remove water from hydraulic fluids through filtration, the most effective way to handle moisture contamination issues is to prevent them from occurring. Hydraulic fluid will absorb moisture from the air if it’s left exposed, so keep your system covered. Make sure that hydraulic fluid in storage is sealed and secure to avoid water contamination.

You can protect against airborne contaminants – and moisture in particular – using Donaldson’s T.R.A.P. (Thermally Reactive Advanced Protection) breathers. T.R.A.P technology strips moisture vapor from intake air and expels moisture back to the atmosphere with each flow cycle. Additionally, the media regenerates its water-holding capacity, resulting in a service life 3 to 4 times that of conventional desiccant breathers.

5. Chemical Contamination

Hydraulic fluid is a chemical, and chemicals degrade naturally over time. This process may happen more quickly in cases where excess pressure or heat is applied to the fluid. Chemical degradation is the second most common source of hydraulic fluid contamination we’ll look at. When hydraulic fluids break down into other chemical components, those secondary chemicals may affect your hydraulic system.

Pay attention to manufacturer guidelines, which will provide information on the expected useful life of the particular hydraulic fluid you’re using. When you commission a new system or perform a routine fluid change, make note of when the next change is due. Additionally, adopting a hydraulic oil analysis program can bring benefits to an operation. An oil analysis report will summarize the condition of the oil, helping to identify any issues that may arise due to chemical or other contamination sources. Make sure you order oil and schedule maintenance time accordingly to minimize hydraulic system contamination.

Also, avoid mixing hydraulic fluids. While the fundamental fluid types may be the same, each manufacturer will employ its own blend of additives to enhance the fluid’s performance and life. If the additives from different fluids are incompatible, it may cause unanticipated chemical reactions, resulting in contamination. 

6. Ingressed Particulate Contamination

Ingressed particulate contamination is the result of any foreign bodies that have managed to penetrate your hydraulic system’s defenses. In plain language: dirt! The specific culprits will depend on where your machinery is operating, but they typically include dust, sand, and mud.

Your system is particularly vulnerable to this type of hydraulic system contamination whenever it is open for servicing or repairs. But you’re also likely to suffer ingress through leaky seals. Don’t risk ignoring leaking seals – it’s not just a question of what’s getting out, it’s also important to consider what’s getting in. You should carry out repairs or maintenance to your hydraulic system in as clean an environment as possible. Clean your machinery thoroughly before opening it to minimize the amount of particulate matter that might enter the system. Consider flushing your system or running your hydraulic fluid through off-line filtration before recommissioning it after the work has been performed. Donaldson Filter Carts, Filter Panels, and Filter Buddy™ offer convenient off-line filtration and flushing and can be used with industrial and mobile equipment.

Lessons Learned

All types of hydraulic fluid contamination pose a threat to the well-being of your equipment. Contamination of a hydraulic system reduces its efficiency, increases cycle time, leads to damage, and potentially results in system failure. If your system is recoverable (and that’s not guaranteed), it may be costly to fix. To avoid contamination issues, flush new or refurbished equipment before commissioning, check and change your filters in line with manufacturer guidelines, minimize contamination, and you’ll maximize your gains!

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