Air springs are widely used in trucks, buses and trailers to support vehicle weight while allowing the suspension height to adapt to changing loads.
Unlike conventional steel springs, air springs use compressed air inside flexible reinforced bellows. In electronically controlled air suspension systems, commonly known as ECAS, sensors and valves regulate the amount of air in the suspension to maintain the required ride height.
When a vehicle sits too low, leans to one side or requires frequent compressor operation, the air spring is one possible cause—but not the only one.
How does an air spring work?
An air spring consists of a reinforced rubber bellows that is filled with compressed air. As vehicle load changes, the pressure required to support the chassis also changes.
In an ECAS system, height sensors monitor the position of the chassis. The control system can then add or release air through the appropriate valves to maintain the required ride height.
This allows the suspension to compensate for changing cargo and operating conditions.
What causes an air spring to lose pressure?
Air springs are exposed to repeated movement, road contamination and environmental conditions. Over time, the rubber bellows can develop cracks, abrasion or leakage.
Leaks may be small enough that the vehicle initially maintains its normal height while driving but gradually lowers after being parked.
However, pressure loss does not automatically mean that the air spring itself is leaking. Air lines, fittings and valves can also allow air to escape.
The location and pattern of the pressure loss therefore provide useful information during diagnosis.
Why does a vehicle sit unevenly?
If one side or axle sits noticeably lower, a leaking air spring is one possible explanation.
The problem can also involve a height sensor, linkage, valve block or pneumatic connection. If incorrect height information reaches the control system, ECAS may add or release air even though the air springs themselves are intact.
For this reason, replacing the bellows solely because the vehicle is sitting unevenly may not solve the problem.
Why might the compressor run too frequently?
Frequent compressor operation can indicate that the air suspension is repeatedly losing pressure or making unnecessary height corrections.
A leak in an air spring or pneumatic connection can cause the compressor to replenish the system repeatedly. Problems with height sensing or valve control can produce similar behaviour.
Excessive compressor cycling should therefore be treated as a symptom of the complete air-suspension system rather than automatically as a compressor fault.
Are visually similar air springs interchangeable?
Air springs can have similar dimensions while differing in load capacity, operating range, mounting arrangement or other construction details.
A replacement should therefore correspond to the intended suspension and axle application. Matching the appearance of the bellows alone is not sufficient.
This is particularly important on vehicles with different axle configurations or electronically controlled suspension systems.
Conclusion
Air springs use compressed air to support vehicle weight and help maintain the correct chassis height. In ECAS-equipped vehicles, they operate together with height sensors, valves and the compressed-air supply.
Air loss, uneven ride height or excessive compressor operation can originate from the air spring, but also from valves, lines, connections or height-control components.
For workshops, considering the complete suspension system helps distinguish a defective air spring from another pneumatic or electronic fault.
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