How a Rotary Screw Compressor Works | AIRducation

How a Rotary Screw Air Compressor Works (Step-by-Step)

If you’ve ever wondered what’s actually happening inside your rotary screw air compressor, here’s the simple breakdown.

What Is a Rotary Screw Air Compressor?

A rotary screw air compressor produces compressed air by trapping air between two rotating helical screws inside a sealed housing called the air end.

This design allows for continuous airflow, making it ideal for manufacturing plants and other demanding industrial environments.

Step 1: Air Intake

Ambient air enters the system through the air filter and passes through the inlet valve into the air end.

The air filter protects the system from contaminants, while the inlet valve controls how much air enters the compressor.

Step 2: Compression Inside the Air End

Inside the air end, two precision rotors, commonly referred to as the male and female screws, begin to rotate.

• Air gets trapped between the rotor lobes and housing
• The space between the rotors gradually decreases
• This reduction in space compresses the air and increases pressure

In oil-flooded compressors, oil is injected during this process to:

• Seal the air between the rotors
• Cool the compression process
• Lubricate internal components

Step 3: Air and Oil Separation

The compressed air and oil mixture exits the air end and enters the sump tank.

This is where separation begins:

• Most of the oil drops out and settles at the bottom
• The air/oil separator removes the remaining oil vapor

Once separated, air and oil continue through the system on different paths.

Step 4: Airflow Path (What Happens to the Air)

After leaving the sump tank, compressed air flows through several critical components:

Minimum Pressure Check Valve

Maintains internal pressure in the system and prevents backflow. This pressure is essential for proper oil separation.

Aftercooler

Reduces air temperature and removes approximately 70% of moisture created during compression.

Moisture Separator

Separates condensed water from the air before it enters your plant’s air system.

From there, clean, compressed air exits the discharge outlet and goes to work.

Step 5: Oil Flow Path (What Happens to the Oil)

Oil is continuously reused in a closed loop system.

Here’s how it flows:

Thermal Valve

Controls oil temperature by routing oil based on its temperature:

• Cold oil bypasses the cooler
• Warm oil partially flows through the cooler
• Hot oil fully routes through the cooler

Oil Cooler

Removes heat from the oil to maintain proper operating temperature.

Oil Filter

Removes contaminants before oil returns to the air end.

Once filtered, the oil is sent back into the air end to repeat the cycle.

Why Rotary Screw Compressors Are Built for Industry

Stationary rotary screw compressors are designed for:

• Continuous operation
• Consistent air supply
• High efficiency under load
• Long-term reliability

That’s why they’re the go-to choice for manufacturing facilities running multiple shifts.

Why Understanding This Matters

When you understand how your compressor works, you can:

• Spot problems earlier
• Maintain proper service intervals
• Protect critical components like the air end
• Avoid unnecessary downtime

And in a production environment, uptime is everything.