Don't underestimate this small jar; if you don't replace it, the brakes might fail.

The braking system is a specialized device used to cause external forces to act on certain parts of a vehicle, prompting the vehicle to undergo a certain degree of braking. Currently, most medium-sized and larger trucks domestically use air pressure braking. The driving safety of a vehicle is closely related to its braking performance, and failures in the braking system that lead to brake failure are the primary cause and a major factor in traffic accidents.

▎1. Why install an air dryer?

In a vehicle's air brake system, the air output by the air compressor contains water vapor and other impurities. If not treated, this water vapor may turn back into liquid water and combine with other impurities, causing corrosion, or even freeze in the air pipes under extreme temperatures, leading to valve failure.

In the past, the treatment of compressed air mainly used the wet air storage tank method, that is, installing a wet storage tank with a drain valve in the air circuit for preliminary drainage. This device has some drying and filtering effect, but it can never completely remove the moisture in the air circuit, and it also requires regular discharge of accumulated water, oil, and other impurities in the storage tank, which is very inconvenient to use.

▎2. The Function of the Air Dryer

The automotive air dryer is used to remove moisture, oil droplets, and other impurities from compressed air. It is installed after the air compressor and before the four-circuit protection valve, used to cool, filter, and dry the compressed air, removing water vapor, oil, dust, and other impurities, providing dry and clean air for the braking system.

Automotive air dryers are regenerative dryers that use molecular sieves as their desiccant. Molecular sieves are synthetic desiccant products with a strong adsorption effect on water molecules. Their main component is an alkali metal aluminosilicate compound with a microporous structure, containing many uniform and orderly channels and cavities.

Water molecules or other molecules are adsorbed onto the internal surface as they pass through the cavities, thereby serving a molecular sieving function. Molecular sieves have a high adsorption-to-weight ratio and can still effectively accommodate water molecules in high-temperature environments of 230°C.

1. Cooling, Separation, Drying

(1) Cooling: The high-temperature compressed air output from the air compressor fully contacts the steel body while passing through the spiral pipeline between the steel body and the outer cylinder, allowing the steel body to absorb and dissipate the heat;
(2) Separation: After cooling, the compressed air rotates at high speed in the spiral channel. Using the principle of centrifugal force, impurities such as oil, water droplets, and dust in the airflow are separated by being deposited on the channel walls.

(3) Drying: Molecular sieve desiccants absorb moisture in the high-pressure airflow to obtain dry air.

2. Automatic Pressure Regulation

The dryer continuously inflates and unloads internally, while the check valve effectively prevents gas backflow, ensuring that the air pressure is always maintained within a certain range, which guarantees the normal operation of the braking system.

3. Desiccant Activation Regeneration and Automatic Drainage

Desiccant activation regeneration and automatic drainage are realized during the unloading exhaust process.

When the dryer unloads, a back-blow airflow is formed. This back-blow airflow carries away the moisture adsorbed on the molecular sieve as it passes through the desiccant, achieving desiccant activation regeneration. This greatly extends the service life of the desiccant, reduces the frequency of dryer replacement, and improves the drying efficiency of the dryer.

At the same time, the back-blow airflow discharges impurities such as oil and metal powder, which have been separated and accumulated in the chamber, into the atmosphere through the exhaust port, achieving the function of automatic drainage. This allows timely cleaning of filtered debris, prevents blockage of the internal air passages of the dryer, reduces the frequency of malfunctions, and also avoids the trouble of manual cleaning. This has a positive effect on the working performance of the dryer and the entire braking system.

4. Safety Pressure Relief  

When the internal air passage of the dryer is blocked, or the pressure regulating valve fails, the internal air pressure will continue to rise. If the air pressure rises to the safety protection pressure, the internal air pressure will act on the exhaust valve, overcoming the spring force of the exhaust valve, causing the exhaust valve to open and release pressure, thereby avoiding danger.  

5. Automatic Heating and Exhaust Silencing  

The automatic heating device consists of an electric heating rod, a temperature control switch, an electrical plug, connecting wires, and other components. The heating device can automatically heat the dryer according to the ambient temperature, preventing the pressure regulating valve and exhaust valve from freezing and avoiding operational failures.  

A silencer is installed outside the exhaust port, which can significantly reduce the noise generated during pressure relief exhaust.  

III. Composition of the Air Dryer  

The air dryer mainly consists of a housing, drying cylinder, pressure regulating valve, exhaust valve, check valve, and heater.

There are three working air ports on the housing, one of which is the air inlet, and the other two are air outlets.

The drying cylinder is sealed and installed on the top of the housing, containing molecular sieve desiccant to absorb moisture and filter impurities. The heating rod inside the heater can warm the dryer, preventing internal moisture from freezing in extremely cold environments.

A check valve is installed in one of the air outlets to prevent dried air from flowing back. The pressure regulating valve and exhaust valve work together to complete the automatic pressure regulation and load-unloading exhaust process.

4. Precautions for Using an Air Dryer

The performance of the air dryer directly affects the quality and service life of the vehicle air brake system. Choosing a good air dryer is crucial to ensure the work stability of the brake system and driving safety.

When using an air dryer, the air compressor should be regularly checked for oil separation issues to prevent excessive oil contamination from causing the dryer to fail.

The drying cylinder of the air dryer contains a desiccant, which has a certain service life and should be replaced according to the maintenance mileage provided by the manufacturer. It is recommended to replace it before winter.

▎Summary:

The air dryer is small in size, multifunctional, easy to replace, and simple to maintain. It has good cooling, separation, and drying effects, with stable and reliable performance, low noise, long service life, and strong load capacity. It is a commonly used automotive component in air brake systems worldwide. However, during use, it is essential to replace it on time to ensure its good performance.