Let’s Talk About Air Supply

Let’s talk about air supply

No, we’re not talking about the Australian 80s pop band. Let’s talk about air supply, as the crucial link between the driver’s brake pedal and the trailer braking system. 

With extended truck service schedules and greater vehicle reliability, it becomes easy to overlook what used to be a daily chore for drivers, that is, checking the air supply is dry and without leaks.

The demands on the truck air supply has increased over the years with more axles and longer trailers. When you add additional functionality, such as a tyre pressure inflation system, lift axles, steer axles and supplementary equipment, that load gets even greater. It becomes a challenge to provide clean, dry air at sufficient pressure through these extended circuits to enable correct operation of these various systems. 


The compressor is the starting point for the air supply system. It needs to be able to supply enough air pressure and flow to ensure all systems can operate correctly. The drive belt, air filter, lubrication and air dryer cartridge all need regular checking and replacement where necessary.

Trailers having difficulties with air springs, or associated systems, should have the pressure checked at the rear-most point on the trailer system when it is connected to the truck and in operation. That is when the system is raising the suspension.

Often, the pressure at the truck’s compressor is nowhere near the pressure reaching the last axle on the trailer. The system must be checked for air leaks, kinked or damaged air lines. If everything is in serviceable condition, a simple solution to a low available air pressure may be to raise the pressure setting of the compressor. However, that is not always possible, especially on an older truck, and even then, it may not overcome insufficient air volume capacity from older air pumps. In these cases, a new air compressor with higher flow rate and/or higher pressure setting would be advisable.


The air system should be checked regularly for contamination by oil or moisture. Traces of oil coming from the compressor are normal, but it must not be any greater than that. Moisture in the system is difficult to eliminate entirely. However, most moisture should be removed by the dryer and regular (daily) drainage of the air supply tank. Most trucks now use automatic drain valves but the operation of these needs to be checked regularly. The system air dryer should be inspected or replaced at regular intervals.

It is important to rectify any problems quickly or it will result in corrosion in brake valves, brake chambers and other pneumatic systems. Lift axle control valves and advanced automatic tyre pressure control systems, such as Hendrickson TIREMAAX PRO, are particularly susceptible to dust and moisture contamination.

Regular checking, cleaning and examination is a vital part of regular air supply maintenance. It is important to remember that the driver also plays a vital part in these precautions.

Let’s talk about air supply