Blowers are critical in industries such as food and beverage manufacturing and pneumatic conveying, as they move air or gas through mechanical systems and provide positive displacement for consistent, reliable airflow. Whether transferring powders, supporting processing lines, or maintaining pressure stability, the blower’s performance directly affects overall system efficiency.
Two of the most commonly used technologies are the screw blower and the Roots blower.
What is a Screw Blower?
A screw blower uses a pair of intermeshing helical rotors within a precisely engineered casing, enabling it to deliver a smooth, continuous stream of compressed air. Its key components include:
- Male and Female Rotors: Rotate in opposite directions, with the male rotor usually driving the female rotor.
- Housing: Encloses the rotors and forms the compression chamber.
- Inlet and Outlet Ports: Regulate the flow of air and maintain the desired pressure.
- Timing Gears: Ensure the rotors remain synchronised without making contact, minimising wear and extending component life.
How Does a Screw Blower Work?
Screw blowers compress air through the rotation of two intermeshing helical rotors, which draw air into their chamber and transport it along the length of the screws.
As the trapped air progresses, its volume is gradually reduced, increasing pressure before it is discharged. This continuous rotary action provides a smooth, pulse-free flow of compressed air, ensuring consistent and reliable performance.
What is a Roots Blower?
Developed by the Roots brothers in the late 19th century, the Roots blower (also known as a rotary lobe compressor) is a type of positive displacement blower that uses two intermeshing lobes to move air from the inlet to the outlet.
The basic operation of a Roots blower involves trapping air in the spaces between the rotating lobes and the casing. As the lobes turn, they carry this trapped air from the inlet side to the discharge side in a continuous motion, enabling a steady and consistent volume of airflow.
How Does a Roots Blower Work?
When air enters through the inlet port and flows into the Roots blower’s chamber, two rotors rotate in opposite directions along the chamber walls. As they turn, they trap pockets of air and carry them from the inlet side to the discharge side, creating a defined airflow path while keeping it at atmospheric pressure (that is, a relatively “lower” air pressure).
Compression does not occur within the chamber itself, and instead, once the rotating lobes pass the opening to the discharge (pressure) side, the air is exposed to the higher system pressure. This sudden pressure equalisation is known as isochoric compression, meaning the pressure increases at nearly constant volume.
The rotors are designed to seal against each other and the casing without physical contact, preventing internal pressure backflow while maintaining efficient air transfer.
Screw Blower vs Roots Blower: What’s the Difference?
Screw and Root blowers are two types of pneumatic blowers with internal mechanics and performance profiles that differ considerably.
1. Structural Differences
A Roots blower operates using two synchronised, non-contact rotating impellers (lobes). As these lobes rotate, they trap gas and physically push it through the space ahead of the blades, creating positive pressure. Roots blowers generate medium pressure (up to 103 kPa).
In contrast, a screw blower uses two intermeshing helical screws that rotate together within a casing to trap air and keep it progressively compressed as it moves along the screws before being discharged. Screw blowers can generate higher pressures than Roots blowers, reaching up to 400 kPa.
2. Working Process Differences
In a Roots blower, the clearance between the two impellers is extremely small, so air enters through the suction port and is continuously carried forward by the rotating lobes into a higher-pressure area. Compression occurs externally when the discharged air encounters system backpressure.
Meanwhile, screw blowers work by trapping gas and letting it move along the length of the screws until the volume between the screw lobes gradually decreases, completing air compression.
3. Differences in Application Scope
Because of its non-contact design, Roots blowers are suitable for applications requiring moderate gas volumes at relatively higher pressure conditions within their operating range, like conveying of granular and powder material.
Screw blowers are typically preferred for applications involving larger gas volumes and stable pressure requirements, like bulk material handling and combustion air supply.
4. Maintenance Cost Differences
Roots blowers feature a relatively simple mechanical structure, contributing to long service life and generally lower maintenance costs.
Screw blowers have a more complex internal design, resulting in high wear and tear requiring regular inspection and servicing to maintain optimal performance. As a consequence, their maintenance costs are typically higher compared to Roots blowers.
Ensuring Reliable, Consistent Airflow for Your Powder Handling Systems
At Pneu Powders Systems, we tailor blower solutions to match your specific material and process requirements. Whether you need blowers for milk powder processing equipment or other bulk powder handling systems, our team works closely with you to identify the optimal technology for your operations.
Partnering with our experts ensures that your pneumatic conveying system delivers smooth, uninterrupted airflow, maximises energy efficiency, and maintains product integrity, keeping your processes reliable, efficient, and cost-effective.
For more insights into components of pneumatic conveying systems, check out our guide on air compressor systems.
