Do you know how to adjust the air pressure of the reservoir?

The air reservoir is a very familiar and simple component, but it is involved in various functions, including the brake system, trailer brake system, clutch booster pump, air horn, airbag adjustment, and many other configurations with pneumatic properties.

The importance of the air reservoir is self-evident. In addition to the regular inspection and replacement of the dryer cartridge, assuming we encounter issues such as slow response in the brake system or slow inflation of airbag seats, how should we manually adjust the air pressure inside the air reservoir?

The air supply commonly used in trucks is drawn in through an air compressor, which takes in external air, passes it through a dryer cartridge, and reaches the APU (Auxiliary Power Unit) air treatment unit. Subsequently, the APU air treatment unit, through a four-circuit protection valve, will reduce the pressure and deliver the gas to various areas of the vehicle. The four-circuit protection valve consists of one intake port and four outlet ports, each supplying air to different regions of the truck that require it. 

Except for some special vehicle models, the APU (Auxiliary Power Unit) air treatment unit serves as the 'commander' for air usage in the majority of trucks. It is responsible for regulating the intake pressure of the air reservoir and transmitting it to different pipelines. Therefore, its importance is no less than that of the dryer cartridge and air reservoir. Hence, when adjusting, we need to pay attention to the following issues.

If a vehicle that has not been modified, it is usually calibrated and handled by the original engineers, and no adjustment is required in the absence of unusual problems.

If our truck is in a normal state, blindly reducing the total pressure can lead to unimaginable consequences. For example, the brake air pressure drops rapidly, and stepping on the brake pedal feels weak. The pressure in the air reservoirs decreases rapidly, resulting in a deterioration of the braking effect. At the same time, a series of components controlled by the auxiliary air pressure will experience various operational issues.

Blindly increasing the total pressure can make the truck brakes overly sensitive. The internal pressure values of various air cylinders and air passages may surge, potentially causing failures in solenoid valves and pipelines. This, in turn, can lead to issues such as the truck being unable to shift gears, the clutch booster pump not working, and the differential lock not engaging. Therefore,under normal conditions, adjusting the pressure of air cylinders individually is unnecessary. Operations should be conducted under the guidance of a service station. 

Of course, if your vehicle encounters low pressure in the brake accumulator while in normal driving conditions and there is no time to go to a service station, you can slightly increase the brake air pressure. The adjustment is also very simple: locate the APU (Auxiliary Power Unit) air handling unit on the vehicle, and using an Allen wrench, insert it into the air intake. By turning it clockwise one or two turns, you can increase the air pressure by one or two units.

At the same time, for some models, the air intake of the APU air handling unit comes with an adjustable screw. Tightening it clockwise by one turn can also increase the pressure by 1 unit. It's important to note that after raising the total air pressure of the entire vehicle, it is necessary to reduce the pressure at the auxiliary air pressure and other exhaust ports. Otherwise, excessively high total pressure input into the auxiliary air pressure cylinder can lead to the aforementioned issues. Blindly increasing pressure does not solve all problems.

Moreover, poor braking performance may not necessarily be solely due to air pressure issues. Components such as the brake system's booster pump, master pump, valve body, brake drums, and brake shoes could all potentially contribute to inadequate braking in trucks. In cases of overloaded transport, even with stable air pressure and no anomalies in the various configurations, the excessive weight of the vehicle can also result in diminished braking effectiveness.

At the same time, owners who have modified or added certain configurations should always pay attention to the working status of the air passages, air reservoirs, and air compressors in their trucks. Increasing pressure can enhance the strength and working pressure of these components. Any additional installations should be carried out under safe conditions, and adjustments to the air passages and air pressure should be done with the assistance of professionals. Blind operations should be avoided.