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How to Reduce Hydraulic Fluid Contamination ben lee

With hydraulic fluid contamination being the cause of more than 75% of hydraulic system failures, it’s important to know how to reduce it.   

Hydraulic fluid contamination can cause many negative effects. For example, it can degrade fluid and prematurely age it. It can also raise the rate of internal leakage which will impact on performance and also decrease the efficiency of components such as motors, cylinders and pumps. Valves that have been affected by contamination will have a greater challenge when it comes to controlling pressure and flow, which will lead to increased heat being generated and wasted horsepower.


That’s not all of the issues hydraulic fluid contamination causes though. It can also make components stick or even seize when there are large amounts of contaminants getting stuck in clearances. This sludge and silting can be very damaging to hydraulic systems.


So where is all this contamination coming from?


A number of sources are involved including system wear, the manufacturing process, exposure to environmental contaminators, servicing and even hydraulic fluids themselves.


Read on to find out ways that hydraulic fluid contamination can be reduced.



Contaminants of hydraulic systems aren’t always solid particles, they sometimes come in the form of liquids, with the most common one being water. Solid particles can cause a lot of damage either by affecting the flow of the system by accumulation or even by reacting with the fluid.

Unfortunately, many new hydraulic fluids can contain high numbers of solid particles that are more than 5 µm in size. This will exceed recommendations coming out of most hydraulic system manufacturers and can be very harmful – especially when you can find over 500,000 particles in just 100 ml of fluid. Standards for cleanliness of hydraulic fluid are plentiful. This actually makes this issue worse.


When it comes to water, contamination can have a number of different effects depending on which system it’s in. It might be that water forms an emulsion or it may be slightly un-mixable (immiscible) and then float on the surface or even sit on the bottom of the fluid. Water can go on to create a lot of corrosion including that done through the process of cavitation. How water gets into the system is puzzling, but most often occurs through flaws in the design, servicing and maintenance or even through internal generation.


Contaminants can enter the system if there is improper storage of fluid in containers or inadequate fluid transfer. They may also enter when components are replaced and through the reservoir breather.


Proper storage

With moisture being so harmful to hydraulic systems, it’s essential to keep hydraulic fluid in proper storage. Even waterproof containers can allow moisture to enter when they are kept in a wide range of temperatures through condensation. By storing containers on their sides, it’s possible to prevent water from accumulating on the tops. In addition, it’s critical to check the lids of containers every so often to ensure that they are tight.


Additives in the hydraulic fluid can also cause degradation of it. For example, there are some additives that contain contaminants that are soluble in the additive, but not in the resulting hydraulic fluid. For example, corrosion inhibitors can create a slime as soon as they come across moisture. Others can create corrosion of steel.


If you opt to flush out the system, unless it’s thoroughly cleaned, you can have contaminated liquids. Although you may know of two fluids that are compatible in theory, as they do not develop a slime or other insoluble material, they will still be contaminated when mixed as they may not retain their individual performance properties.


In summary, the best way to reduce hydraulic fluid contamination is to use good handling and storage processes. Maintenance and flushing will need to be undertaken with care when cleaning out the system properly or by draining out the old fluid, and adding new fluid a handful of times to ensure a 95/5% mix. 

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