1 / 04 / 2022

What Do Hydraulic Filters Do and Why Are They Important?

From pumps and valves to motors and cylinders, hydraulic systems comprise many complex components. However, the contained hydraulic fluid used is undoubtedly the most important element of any system.

The mechanics behind hydraulics means that without the fluid, the system simply wouldn’t be able to run. For this reason, any variation in the hydraulic fluid used can lead to system failure. This can be anything from incorrect fluid level, fluid properties or contamination.

In fact, industry analysis has indicated that up to 90% of hydraulic system problems are the result of fluid contamination.

With contamination presenting such a great risk to hydraulic systems, how do we prevent it? This is where hydraulic filtration comes in.

What is a hydraulic filter?

Hydraulic filters are implemented in a hydraulic system to keep the fluid free from contaminants. Filtration works by continuously removing contaminants to keep the fluid clean.

The process of purifying the contents ensures that the system is protected from the damage that can be done when foreign particles enter the system.

There are many different types of filters, and typically more than one type will be found in every hydraulic system. Filters can be located at various points in the hydraulic system, some of the most common types are:

  • Suction filters – Positioned before the pump, and work to prevent larger dirt particles from entering and possibly damaging the pump.
  • Pressure filters – Positioned after the pump, and ensure that the fluid is cleaned after exiting the pump and before entering the circuit.
  • Return line filters – Low-pressure filters which purify the fluid just before it returns to the reservoir, filtering out any dirt that may have accumulated from the pump and actuators.
  • Off-line filters – Small independent filtration sub-systems which consist of a filter, pump, motor and hardware connections. These filters operate when the machine is not active to ensure that the fluid maintains a constant contamination level.
  • Air filters – Sometimes known as air breathers, these are used to filter the air brought into a system. Without an air filter, dirty air may be drawn into the reservoir and quickly contaminate the fluid contents.

hydraulic filtration

How does a hydraulic filter work?

Aside from off-line filters, all other hydraulic filter types work in the same way no matter where they are located in the system.

Essentially, any fluid entering the system will enter through the inlet port of the filter. The fluid will be cleaned as it flows through the filter, and pumped out through the outlet port.

An off-line filter has an independent pump that draws the fluid out of the reservoir, and through the filter. Once filtered, the fluid returns to the reservoir and the cycle repeats continuously.

By design, hydraulic filters should remove contaminants as efficiently as possible, whilst ensuring that the filter element retains most of the dirt without clogging.

Why hydraulic filters are important

Anyone who works with hydraulics will agree that equipment and running costs can be a substantial investment for any business, no matter the scale of the application.

As mentioned previously, fluid contamination is one of the leading causes of system failure. When considering the costs involved, filtration is key to protecting the system and preventing any foreign particles from disrupting its flow.

By definition, contamination is ‘anything in the system that is not supposed to be there’. Therefore, this can mean anything from water to air to dirt, and good quality filtration can control all of these.

Common causes of hydraulic contamination

You may be wondering, how can dirt enter a closed hydraulic system? There are many reasons. These include:

  • Introduced contaminants – If a system component requires repair or replacement, particles may enter the system through seals or breather caps when opened. Similarly, if unfiltered fluid is added to replenish the supply, this may introduce foreign particles.
  • Built-in dirt – This is typically caused by any particles generated from assembling or repairing the system such as metal chips, weld splatter and abrasive dust.
  • Internally generated particles – General wear and tear of system components during operation can contribute to fluid contamination, which may be generated from movements such as friction of moving parts.
  • Fluid breakdown – It’s possible that chemical reactions may occur in the reservoir, which can lead to the formation of a sludge type material and acids. This can lead to clogging and the corrosion of system components, resulting in a build-up of dirt particles.

hydraulic oil leak

How contamination affects system performance

The effects of contamination begin with the hydraulic fluid before being carried into the system. Over time, this contamination can build up and continuously worsen. For any system, this can have catastrophic consequences.

The presence of contamination can lead to the following conditions:

  • Corrosion – Fluid degradation can quickly lead to corroding any component in its path as it is carried through the system.
  • Leakage – The presence of dirt in a system can lead to internal leakage, which has a direct impact on the performance of valves, pumps, motors and cylinders.
  • Sticking parts – Contamination can cause components such as valves to start sticking. When this happens, the spool cannot change positions under normal force conditions, resulting in reduced performance and efficiency.

None of these conditions are desirable for any hydraulic system, which is why good quality filtration is crucial for optimising performance and increasing lifespan.

Criteria for selecting a hydraulic filter

Every hydraulic system’s individual filtration needs are completely unique, so there’s certainly no one-size-fits-all solution.

As discussed earlier, hydraulic filter components are designed depending on where they are to be placed within the system. The type of filter you need will first and foremost depend on its positioning, and from there, the most suitable filtration option should be chosen depending on the following factors:

  • Type of hydraulic fluid
  • Operating pressure
  • Operating temperature
  • Fluid flow per cycle
  • Required resistance of filter
  • Allowed system pressure drop
  • Ease of element maintenance

Proper hydraulic filter selection will ensure that the level of dirt within the system stays at an acceptable level. Removing all dirt completely is unlikely and unnecessary, so filter choice and placement should be in line with a sustainable dirt level that your system can allow.

If you’re in need of some more guidance in regards to filter selection, or any advice on hydraulic components, get in touch with Primary Fluid Power.

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