Roots Blowers vs Screw Blowers: Which Positive Displacement Blower Is Better?

In industrial air and gas handling, choosing the right Positive Displacement Blower can directly impact efficiency, reliability, operating costs, and long-term performance. Among the most widely used technologies are Roots blowers and screw blowers. Both fall under the positive displacement category, meaning they move a fixed volume of air or gas per revolution regardless of pressure, but their internal designs, performance characteristics, and ideal applications differ significantly.

This article offers a comprehensive, experience-driven comparison of Roots blowers and screw blowers. By the end, you’ll understand how each works, where each excels, their advantages and limitations, and how to determine which Positive Displacement Blower is better suited to your specific needs.

Understanding the Positive Displacement Blower Concept

A Positive Displacement Blower operates by trapping a fixed amount of air or gas and forcing it through the system. Unlike centrifugal blowers, airflow is largely independent of pressure, making these machines ideal for processes requiring consistent volume across varying system resistance.

Key characteristics of positive displacement blowers include:

• Constant airflow regardless of pressure changes
  
  

• High reliability in demanding industrial environments
  
  

• Suitability for vacuum and pressure applications
  
  

• Predictable performance and easy control
  
  

Roots blowers and screw blowers are two dominant technologies built on this principle, each with a different mechanical approach.

What Is a Roots Blower?

A Roots blower, sometimes called a lobe blower, uses two or three lobed rotors that rotate in opposite directions inside a casing. These rotors do not touch each other or the housing. As they rotate, air is trapped between the lobes and the casing and carried from the inlet to the outlet.

How Roots Blowers Work

• Air enters the inlet side of the casing
  
  

• Lobes rotate and trap a fixed volume of air
  
  

• Air is pushed to the discharge side
  
  

• Compression occurs externally in the system, not inside the blower
  
  

Because compression does not happen internally, Roots blowers are often described as “constant volume” machines.

What Is a Screw Blower?

A screw blower uses two intermeshing helical rotors, typically referred to as male and female screws. As these rotors turn, air is drawn in, trapped, and progressively compressed as it moves along the rotor length toward the discharge.

How Screw Blowers Work

• Air enters the suction port
  
  

• Intermeshing screws trap and compress air internally
  
  

• Pressure builds gradually along the rotors
  
  

• Compressed air exits at the discharge
  
  

This internal compression is a defining feature and a key reason screw blowers often achieve higher efficiency.

Key Design Differences Between Roots and Screw Blowers

Understanding the mechanical differences helps explain performance variations.

Rotor Geometry

Roots blowers rely on lobed rotors with uniform volume, while screw blowers use helical rotors with decreasing volume chambers. This fundamental difference influences efficiency, noise, and pressure capability.

Compression Method

• Roots Blower: No internal compression; pressure increases after discharge
  
  

• Screw Blower: Internal compression occurs within the blower
  
  

This internal compression allows screw blowers to match system pressure more closely, reducing wasted energy.

Efficiency Comparison

Efficiency is often the deciding factor when selecting a Positive Displacement Blower.

Roots Blower Efficiency

Roots blowers are mechanically simple but less energy-efficient, especially at higher pressures. Because air is not compressed internally, there is often a sudden pressure rise at discharge, leading to energy losses.

Efficiency characteristics include:

• Best suited for low to moderate pressure
  
  

• Efficiency drops at higher pressure ratios
  
  

• Higher power consumption compared to screw blowers in many cases
  
  

Screw Blower Efficiency

Screw blowers are widely recognized for superior efficiency due to internal compression. They can be optimized for specific pressure ranges, significantly reducing energy losses.

Efficiency advantages include:

• High efficiency across a wide pressure range
  
  

• Lower specific power consumption
  
  

• Reduced energy costs over time
  
  

From an operational cost standpoint, screw blowers often outperform Roots blowers, particularly in continuous-duty applications.

Noise and Vibration Levels

Noise is a major concern in industrial environments, affecting worker safety and facility compliance.

Roots Blower Noise

Roots blowers are known for higher noise levels due to:

• Pulsating airflow
  
  

• Sudden pressure changes at discharge
  
  

• Minimal internal damping
  
  

Noise control measures such as silencers and acoustic enclosures are often required.

Screw Blower Noise

Screw blowers operate more smoothly due to continuous internal compression, resulting in:

• Lower noise levels
  
  

• Reduced pulsation
  
  

• Less vibration
  
  

For noise-sensitive environments, a screw-type Positive Displacement Blower is often preferred.

Pressure and Flow Capabilities

Roots Blowers

Roots blowers excel at delivering high volumes of air at relatively low pressures. Typical characteristics include:

• Strong performance at low pressure differentials
  
  

• Limited efficiency at higher pressures
  
  

• Reliable airflow even with system fluctuations
  
  

They are commonly used where large airflow is more important than high pressure.

Screw Blowers

Screw blowers handle higher pressure applications more effectively. Their capabilities include:

• Efficient operation at medium to high pressures
  
  

• Stable flow with reduced pulsation
  
  

• Better adaptability to variable process demands
  
  

When pressure requirements increase, screw blowers usually become the more practical Positive Displacement Blower option.

Maintenance and Reliability

Maintenance requirements can significantly affect total cost of ownership.

Roots Blower Maintenance

Roots blowers are mechanically simple, which translates to:

• Fewer components
  
  

• Easier servicing
  
  

• Lower initial maintenance complexity
  
  

However, the absence of internal compression can increase mechanical stress on downstream components.

Screw Blower Maintenance

Screw blowers have more complex internal geometry, leading to:

• Higher precision manufacturing
  
  

• More attention to lubrication and clearances
  
  

• Slightly more complex maintenance procedures
  
  

That said, modern screw blowers are highly reliable and often require less frequent maintenance due to reduced mechanical shock and vibration.

Initial Cost vs Long-Term Cost

Roots Blower Costs

Roots blowers generally have:

• Lower initial purchase price
  
  

• Simple installation
  
  

• Higher operating and energy costs over time
  
  

They are often selected for budget-sensitive projects or intermittent use.

Screw Blower Costs

Screw blowers typically involve:

• Higher upfront investment
  
  

• Advanced design and controls
  
  

• Lower energy and lifecycle costs
  
  

In continuous or energy-intensive operations, the long-term savings of a screw blower can outweigh its initial cost.

Typical Applications

Common Roots Blower Applications

Roots blowers are widely used in:

• Wastewater treatment aeration
  
  

• Pneumatic conveying
  
  

• Vacuum packaging
  
  

• Combustion air supply
  
  

These applications benefit from high airflow and robust, straightforward operation.

Common Screw Blower Applications

Screw blowers are commonly found in:

• Industrial aeration systems
  
  

• Food and beverage processing
  
  

• Chemical and petrochemical plants
  
  

• Power generation support systems
  
  

Where efficiency, low noise, and stable pressure are critical, screw blowers dominate.

Environmental and Energy Considerations

Energy efficiency and sustainability are increasingly important in modern industry.

Roots blowers, while durable, generally consume more power per unit of air delivered at higher pressures. This can lead to increased carbon footprint and higher energy bills.

Screw blowers align better with energy optimization goals. Their efficient compression reduces wasted energy, making them more environmentally responsible in long-term operations.

How to Choose the Right Positive Displacement Blower

Choosing between Roots and screw blowers depends on several factors:

Consider Roots Blowers If:

• Your application requires high airflow at low pressure
  
  

• Budget constraints are a major factor
  
  

• Operation is intermittent rather than continuous
  
  

• Maintenance simplicity is a priority
  
  

Consider Screw Blowers If:

• Energy efficiency is critical
  
  

• Noise reduction is important
  
  

• Your system operates at medium to high pressures
  
  

• Long-term operating cost matters more than upfront price
  
  

The “better” Positive Displacement Blower is not universal; it depends entirely on your operational priorities.

Final Verdict: Which Is Better?

When comparing Roots blowers vs screw blowers, the answer to which is better depends on application, pressure requirements, and lifecycle cost considerations.