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8 Things You Need to Know About Hydraulic Oil Contamination

Comprehending the condition of your hydraulic fluid and knowing how to retain its cleanliness is the secret to giving your components a long life.

You may have learned a lot in college, university or even your apprenticeship, but you may not have had information on contamination packaged together in one place quite like this. Read on to access a concise overview of why you have to keep those contaminants out of your oil.

1. Know the types of contamination
Contaminants are surprisingly varied but those that cause the most damage include water, gases, particulates and even bacteria. When the temperature starts to rise and contaminants are present, then things can only go downhill; lubricants and oils start to degrade, oil break down and flow can collect discharge that is electrostatic.

2. Where is it coming from?
Surprisingly, there can be a lot of contamination in new oil. It can be cross contaminated, contain additives and be a victim to dust by not closing filler caps and being in the wrong storage. Only around 10% of hydraulic system contamination can be caused by system-generated wear.

It’s possible that additives can split from the oil and cause a lot of clogging of filters. Soft and sticky stuff can suddenly block the filter causing issues.

3. Recognise the dangers
unless the contaminants are large, and they drop to the bottom of the tank, they are going to create mayhem and damage as they flow around the system.

The contaminants that create the most damage are usually between 1 and 20 µm. Those that are smaller or larger can also create serious damage, but the larger the particles are, the more likely you can capture them. If they’re not removed and left to their own devices, they will get ground down into smaller particles. Those particles that are very small can be hard to catch, and they can also collect together and stick up the valves too.

Water is a contaminant that is very difficult to deal with. It can corrode and break down the chemistry of the oil so that lubrication factor no longer works effectively. Once you get water in the oil and warm weather comes along, then bacteria can develop. The most cost effective way to handle this is to stop water from getting into the system. Once it’s in it, it’s hard to get it out and will usually cost you.

Air is at the core of cavitation, in addition to the breakdown of fluids and growth of bacteria. That’s why we recommend that you submerge return pipes.

4. Don't forget filtration
Effective filtration is a habit that will help incredibly to keep your system clear. Of course, filters need to be designed to be able to handle flow rates, viscosity and different sized particles. A 10 µm absolute filter works very well and we suggest using one of that size over others.

5. Follow the ISO Code
The International Standards Organisation 4406 code is a form of measurement when it comes to how many particles are in a sample of oil. The result will usually be a 3-digit number and will come from a sample of between 1 ml and 100 ml.

It’s also used by manufactures to suggest how clean the oil should be in order to attain the optimal performance. To give you an idea of what is a typical measurement, in a 1ml sample of new oil you can find as much as 20,000 particles that are larger than 4 µm.

6. Don't make costly mistakes
Although it can get expensive to buy filters and other equipment to control contamination, not buying it can be even more expensive. You will retain a greater lifespan for your components by keeping your oil clean.

7. Remember service intervals
All oil will only last so long, and it could well be that you will need to change it regularly. By using filers and going out of your way to keep it clean, you can extend the amount of time between changes.

8. Take proper oil samples
Periodically, it’s necessary to change oil. Being heated for operation and then being pumped around a system that may have cavitation and other degradation going on, can result in the collection of particles and chemical degradation. You can compare a sample against a sample from the new oil to check for changes.

Always take a sample when you start the machine and continue to take samples over time to get an understanding of where the oil is in its lifecycle. You will need to plot the data.


It’s always better to prevent rather than cure. Go all out to stop human error from contaminating oil and address any other contaminations that have appeared in your oil. Gases, water, particulate and bacteria can all cause serious problems and should be removed as much and as soon as possible from the hydraulic system. You will enjoy greater performance and longer component life.


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