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How Does Semi-Truck Air Compressor Work?

How Does Semi-Truck Air Compressor Work?

The brakes and air suspension are essential components of the semi-truck. They require pressurized air to perform their function. Each semi-trailer is equipped with a pressurized air system consisting of an air compressor to operate the braking system.

How Does Semi-Truck Air Compressor Work? The air compressor in a semi-truck inhales the atmospheric air, compresses it to increase pressure, and sends it to the braking system. It is present on either side of the engine, and each truck has one compressor which can last for 15 years. Air leakage oil in the air system and fault in the brake compressor drive are signs of a failing compressor.

A functional air compressor is essential for the safety of the vehicle and driver. Any minor fault in it can cause great mishaps. The driver won’t be able to apply brakes on time, and accidents can happen. So choose high-quality equipment for your vehicle to avoid all the troubles.

What is the air compressor in a semi-truck?

The semi trucks do not have ordinary braking and suspension systems as those present in the small automobiles. These heavy-duty vehicles have air brakes that use compressed air to press the brake pedals.

An air compressor is an essential component of the air braking system. It is also a source to deliver compressed air to the air suspensions and other parts of the semi-trucks.

As the name indicates, its main function is to compress the air at high pressure and transfer it to the braking system or the suspensions of the vehicles. Compressed air provides the necessary force or energy for all these systems to function accurately.

How does a semi-truck air compressor work?

The primary function of the air compressor is to maintain the availability of the compressed air at the desired pressure. It usually consists of a pump, a reservoir, and a governor to maintain the air pressure.

The truck engine supplies the necessary power to perform its functions. It either takes the air from the outside environment at the atmospheric pressure from the air cleaner or from the vehicle’s turbocharger.

Then it compresses the air with a pump to increase the pressure and direct it towards the reservoir. The governor plays a main role in determining the maximum and minimum air pressure in the reservoir and also monitors when it is required to deliver the compressed air to the desired system.

In a braking system, compressed air is always required at a preset pressure. The governor monitors the air build cycle of the compressor, which governs when it is necessary to pump the compressed air into the system.

In this situation, the compressor is running loaded. When the pressure in the reservoir increases that of the preset maximum level, the compressor turns over, known as running unloaded.

When the pressure is above the preset level, it stops it from further working and causes the air dryer to get rid of excessive air.

In case of lower pressure than the preset minimum level, it activates the running loaded cycle to increase the air pressure inside the system.

The water vapors, oil droplets, and lubricating oil get mixed with the air during compression. The air dryer in the air system helps remove these oil particles. The discharge lines are used to transfer compressed air to the reservoir.

The temperature inside the air dryer helps remove the oil droplets and water vapors. The air dryer easily removes the droplet if the compressed air is at normal temperature. But the droplets can pass easily if the air is at a high temperature. To overcome these issues, the discharge lines have a greater diameter to decrease the air temperature.

The compressed air then travels towards the primary and secondary brake system reservoirs. The primary brake system reservoir is filled first, and the secondary reservoir is filled later.

After this, the compressed air is ready to be delivered to other truck components. The pressurized air is also used in the suspension and transmission system of the vehicle.

The duty cycle is a crucial factor in determining the efficiency of an air compressor. It is the ratio of the time to generate pressurized air relative to the running time of the engine.

Ideally, all types should have a low value of the duty cycles. Compressors with high-duty cycles can cause problems like increased temperature of the pressurized air.

It can cause a fault in the air braking system of the semi-trucks. The duty cycle of the semi-trailers is approximately 25%

Number and mounting position of the air compressor in a semi-truck

Almost all models and brands of semi-trailers contain only one air compressor to provide pressurized air to all systems. Semi-trucks are heavy vehicles, and they require more power to stop them.

The pressurized air systems in these trucks are more efficient than those in small vehicles. Their capacity for air is higher than other types of compressors.

It is driven by the truck’s engine and has two cylinders. Its capacity depends upon the manufacturer and its size.

Its capacity is usually measured in gallons or liters. The compressor in heavy trucks can have a capacity of up to hundreds of gallons.

They continuously supply pressurized air as long as the engine is running. It is usually mounted on the right side of the engine. It is connected to the engine through the gear wheel.

The type of compressor installed in a truck depends upon the manufacturer. Most of them take only 40 to 45 seconds to build pressure up to 130psi.

How to tell if the air compressor is worn out?

The semi-truck air compressors are made from a durable material, but they get worn out over prolonged use. Like other machines, this tool also shows some clear signs if it is failing or getting bad. 

Here is a brief list of all the signs of a failing compressor.

  • Air leakage
  • The compressor won’t start
  • The compressor won’t stop
  • Compressor fails to build Air pressure
  • Oil and water vapors in the discharge lines
  • Air brake compressor drive failure

Besides keeping an eye on all these signs, you should regularly perform the air leakage test. It is crucial to check the integrity of the compressor before starting the drive.

First, park the semi-truck on an even ground and chock the wheels. Then, let the system build the pressure to its full potential. After this, turn off the engine, but keep the keys on the ignition to read the pressure readings.

After this, press the brake pedals down for 2 to 3 minutes. Then, look at the pressure gauge to note the pressure readings. It should not be more than 5psi for two minutes if leakage is present.

You can also check the lower pressure audible warning alert through this test. Press the brake pedal continuously to release the air from the system. When the pressure is below 60psi, the audible warning alert should make a noise.

How long do air compressors last in semi-trucks?

This equipment also undergoes wear and tear due to overheating and other issues. They can also get worn out after prolonged use.

In such cases, it is better to replace them with a new one. On average, it can last for 10 to 15 years in a semi-trailer. Some high-quality air compressors can last for more than 15 years.

The drivers should check for minor faults and defects in their parts to make them last longer. Inspect it regularly for the presence of corrosion filth or other particles that can obstruct its working.

It is better to schedule a service regularly by a professional mechanic to improve its functioning. Regularly perform the air leakage test to rule out all the leaking issues before starting the vehicle.

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