Finding water inside an HGV air reservoir is a sign that deserves attention.
Atmospheric air naturally contains moisture, and the process of compressing that air can lead to condensation. The vehicle’s air-treatment system is designed to remove most of this moisture before it reaches the reservoirs.
If significant amounts of water repeatedly appear in the tanks, the air dryer or another part of the pneumatic system may need investigation.
Where does the water come from?
The compressor draws ordinary atmospheric air into the pneumatic system.
That air contains water vapour.
When it is compressed, its temperature rises. As the compressed air later cools, moisture can condense.
Without effective drying, that condensation can accumulate within:
- Air tanks
- Valves
- Brake components
- Pipework
- Suspension components
Isn’t the air dryer supposed to stop this?
Yes.
The air dryer removes moisture before compressed air is distributed around the vehicle.
Knorr-Bremse states that moisture within commercial vehicle compressed-air systems can contribute to corrosion, premature wear and potentially freezing.
If water repeatedly reaches the reservoirs, possible causes can include:
- Saturated dryer cartridge
- Dryer fault
- Purge valve problem
- Incorrect servicing
- Excessive compressor contamination
- Unusually high pneumatic demand
Does a small amount of moisture always mean something is wrong?
The amount, frequency and vehicle design all matter.
Finding a trace of moisture does not necessarily identify a specific failed component.
Repeated or excessive accumulation, however, gives technicians a reason to inspect the air-treatment system rather than simply draining the reservoirs and carrying on.
Why is water in an HGV air system a problem?
Moisture can cause several problems.
Corrosion
Water can contribute to corrosion within reservoirs, pipework and other metal components.
Freezing
In low temperatures, accumulated moisture can freeze and interfere with pneumatic components.
Valve damage
Contaminated air can affect the operation and service life of control valves.
Increased maintenance
Once moisture and contamination begin moving downstream, several components may start experiencing problems rather than one isolated failure.
Could compressor oil also be involved?
Yes.
Compressed air may contain compressor oil aerosols as well as moisture.
Some dryer cartridges incorporate oil separation specifically to reduce contamination before air enters the wider system.
Excessive oil contamination can therefore justify investigation of both the compressor and air-treatment equipment.
What should be checked?
If excessive water is found repeatedly, a workshop may consider:
- Dryer cartridge condition
- Air dryer operation
- Purge cycle
- Compressor condition
- Reservoir contamination
- Related valves and pipework
Correct service requirements vary between vehicle and component manufacturers, so the applicable maintenance information should always be followed.
Need air-treatment components?
AutoFast supplies air dryers, cartridges, valves and other HGV parts for commercial vehicle pneumatic systems.
Supplying the vehicle information and the number from the existing component can help our team identify the correct part for your application.
