The importance of regular air dryer filter cartridge changes

air dryer filter cartridge used

Air dryer filter cartridges

Although a humble service part, air dryer filter cartridges play an important role within the compressed air system.  Typically part of the air dryer assembly, the filter cartridge is designed to remove any contamination in the air supply produced by the vehicle’s compressor.

Contaminants include oil, water and aerosols, all of which can reduce the lifespan of components downstream, leading to increased maintenance costs and downtime.  Excess water during the winter season can cause freezing pipes leading to blockages.  Furthermore, oil and aerosol contamination risks perishing rubber components within the air valves downstream.

Manufactured by OEMs including Haldex, Knorr-Bremse and Wabco, bus air systems tend to be fitted with one of two air dryer filter types: Conventional, which tend to be fitted to older vehicles and have a single desiccant filter element to remove water, and oil separator cartridges featuring both a desiccant filter for water and an oil element to remove oil and aerosols.  Oil separator cartridges have a longer service life and are recommended for vehicles with high air consumption.

Providing the air system has been depressurised, the cartridges are easy to fit with quick simple process.  Change intervals vary depending on vehicle operation.  For example, buses providing urban services have a high air consumption due to high braking demand and require shorter replacement intervals compared to vehicles on rural routes with lighter braking demand.

As a long-standing OEM parts supplier to the PSV industry, Imperial Engineering has a wealth of air system knowledge, so we recommend a minimum of a yearly filter cartridge change for buses with high air consumption.  We’re also pleased to support operators with technical advice and guidance.

To help, we’ve identified the following routine service tips relating to air systems:

  • Operating the air reservoir drain valves is the quickest way to check filter functionality. Clean dry air depleting from drain valve is a good indication the filter is operating correctly.  If water, oil or both (yellow mixture) emerge from the drain valve, the filter needs changing.
  • Always check the compressor for oil carry over when changing the filter.
  • Vehicles with slow air build-up times can indicate a blocked filter cartridge due to age or excess oil/water carry over.
  • Ensure the ‘purge’ function is working correctly on the air dryer assemblies. this can be checked by building up the vehicle air pressure.  Once the air reservoirs have reached operating pressure, you should hear a burst of air from the air dryer.  This is the purge function working, enabling contaminates in the filter to be exhausted, as well as drying the desiccant in the filter.
  • Always check for air leaks, as they can increase the duty cycle of the compressor and air dryer, increasing the volume of air passing through the filters, shortening their lifespan.
  • Checking exhaust ports/silencers on other air valves (e.g. EBS modulators, relay valves) for excess oil/water could indicate a badly functioning filter cartridge.

For further information, please call Imperial Engineering on 01992 634255, or email