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Contamination in Hydraulic Systems ben lee

How to Minimise the Damage from Contamination in Hydraulic Systems 

It’s no secret that contamination in hydraulic fluid systems can cause no end of issues. If you’ve been following our blog posts for a while, you’ll know that basically efficiency is increased by minimising gaps and clearance between moving parts. But whatever you do with this, particles can and will abrasively wear against components and can even lodge themselves in valves.


Contaminants can be easily introduced, for example with the addition of a component that is not fully clean. Manufacturers are aware of the trouble that contaminants can cause and they will try to improve matters for us mere mortal engineers. Here’s how manufacturers of hydraulic equipment minimise contamination:

  1. Determine limits of contamination for any new components
  2. Check that component contamination do not pass established contamination limits
  3. Flush the system to achieve target of roll off cleanliness 

As with any other engineering, identifying suitable contamination limits is about analysis costs/benefits. Although it’s obvious that a clean part is preferred to a dirty part, there is of course a cost associated with achieving that cleanliness. Therefore it’s important to the sensitivity of contamination and the working pressure of the system to establish the correct limits of contamination.


The measurement of contamination limits is specified in milligrams (mg) and length (longest chord) of the largest particle present.


Verify the Cleanliness Level

It’s possible to remove contamination from hydraulic components by rinsing them under pressure, using an ultrasonic cleaning device and giving functional bench-test methods. Using an extraction fluid such as a petroleum distillate is preferred as it does not encourage rust nor does it interfere with the filter membrane used to measure the level of contamination.


Recently an engineering organisation tested contamination levels of over 100 new hydraulic system components. Within their collection they looked at pumps, reservoirs, tubes, hoses, valves and other fittings. They found more than 8mg of dirt and debris on one of out of three of the components. All of this can be taken through the rest of the hydraulic system upon start-up of the machine.


Contamination is produced during any manufacturing or adjustment process. Even cutting a hose can create particles of rubber and metal. Performing the task of machining a valve manifold will create cutting chips. Welding spatter is produced from fabricating a steel reservoir and welding can also introduce iron-oxide. In every situation components should be prepared for use before adding to a fluid power system.


As new systems are put together, it makes sense to check what their contamination level is. This is a common activity for manufacturers to undertake as part of a testing procedure whilst systems are still being put together on the assembly line.


Using online portable particle counters is the preferred approach for verifying the level of cleanliness. These types of particle counters provide a rapid result and they don’t come with the issues that bottle sampling can.


Under certain circumstances, it’s possible to clean the system by cycling the actuators. If the fluid is not returned fully to the reservoir by the components, then it might be necessary to use an auxiliary flushing cart to attain the correct cleanliness level.


Once a system has been assembled, cleansed and then shipped, it needs to remain sealed in order to prevent any contamination from occurring. Keep in mind that engineers have observed that it can do more harm than good to perform oil changes during the first 2000 hours of machine operation. This is because new oils are not always clean and it’s often the case that end users don’t have the required equipment for filtering the fluid.


It’s vital to start the machine with a clean hydraulic system if you’re looking for a reliable and long equipment life. It’s the only way that you’ll be able to minimise it’s contamination from the outset and hopefully be able to continue to keep control over what’s going into your system and how much damage it does to components.

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