Air Compressor Principles and Components: A Comprehensive Overview

Air compressors are essential in many industries, providing compressed air for tools and equipment. Understanding how they work and their key components can help improve their efficiency, reduce maintenance costs, and extend their lifespan. Let’s take a look at the main parts of an air compressor and how they operate.

1. Electric Motor of Air Compressors

The electric motor powers the compressor, driving its core components. Motors for air compressors usually fall into two categories:

• Motors below 250 kW use a 380V motor.

• Motors above 250 kW typically use 6 kV or 10 kV motors.

Explosion-proof air compressors often use 380V/660V motors. These motors can operate at pressures up to 0.8 MPa, although the standard rated pressure is 0.7 MPa.

Most compressors use 2-pole and 4-pole asynchronous motors.

• A 2-pole motor runs at 3000 RPM, while the asynchronous motor runs at around 2910 RPM.

• A 4-pole motor runs at 1500 RPM, while the asynchronous motor runs around 1455 RPM.

Motors usually have a service factor between 1.1 to 1.2. This means the motor can provide up to 15-20% more power than its rated capacity. For example, a 200 kW motor can reach up to 230 kW with the service factor.

2. Screw Compressor Main Unit

The heart of a screw compressor is the main unit (also called the compressor head). It consists of two rotors: the sun rotor (male) and the moon rotor (female). These rotors mesh together to compress air and increase its pressure.

The main components of the compressor head include:

• Rotors

• Cylinder (housing)

• Bearings

• Seals

The rotors do not touch each other, leaving a small gap of about 2-3 microns. This reduces friction and extends the compressor’s life.

3. Oil Separator and Separation Mechanism

The oil separator separates oil from the air mixture. It’s made from carbon steel and contains a special filter called the oil separator filter. The filter is made of multiple layers of glass fiber that trap oil as the air passes through.

How It Works:

• The oil-air mixture enters the separator at high speed.

• Centrifugal force pushes the oil against the separator walls, while gravity pulls it to the bottom.

• The oil is then returned to the system for reuse, ensuring the air leaving the compressor is clean.

By the time the oil-air mixture reaches the filter, 99% of the oil has already been separated.

4. Cooling System of Air Compressors

Air compressors use either an air-cooled or water-cooled system to manage heat.

• Air-cooled systems use a radiator-style cooler with a fan to cool the air. This is the most common cooling system.

• Water-cooled systems use a tube-and-shell heat exchanger. Here, water flows through tubes, while oil and gas pass through the surrounding shell. This system requires a cooling tower for water circulation.

In both systems, the cooled air flows through a minimum pressure maintenance valve before leaving the compressor.

5. Temperature Control Valve

The temperature control valve regulates the oil temperature entering the compressor. Its job is to keep the oil temperature within a safe range.

• When the oil is below 70°C, the valve keeps the oil from entering the cooler.

• When the oil temperature exceeds 76°C, the valve allows all hot oil to pass through the cooler.

This valve ensures proper lubrication and prevents the formation of emulsified oil, which can damage the system.

6. PLC and Display Screen

The PLC (Programmable Logic Controller) is like the brain of the compressor. It monitors all key components and stores data on performance. The display screen shows the status of the compressor, including:

• Pressure

• Temperature

• Oil levels

It alerts operators when it’s time to replace filters, oil, or other key components. It also provides diagnostic information in case of any problems.

7. Other Key Components of a Screw Compressor

Several other parts help the compressor run smoothly:

• Air Filters: These filter out particles larger than 3 microns, protecting the compressor’s components.

• Inlet Valve: Controls the air entering the compressor, adjusting the compressor’s output.

• One-Way Valve: Prevents oil from flowing back into the compressor.

• Pressure Sensor: Monitors the pressure after the oil separator. It triggers a maintenance alert when the pressure changes.

• Temperature Sensor: Measures the temperature of the air leaving the compressor to prevent overheating.

• Oil Filter: Removes contaminants from the oil to ensure smooth operation.

Conclusion: Key Takeaways

Understanding the principles and components of an air compressor can help you maintain and operate it more effectively. Regular maintenance of components such as the oil separator, filters, and cooling system ensures the compressor runs efficiently for longer periods.

By monitoring critical data via the PLC controller, operators can quickly identify problems and avoid costly breakdowns. With proper care, an air compressor can perform at its best, providing reliable compressed air for industrial applications.