What Is Roots Blower Used For

A roots blower is a positive displacement rotary lobe machine used to move air and gas at low to medium pressure. It is used wherever constant airflow is required regardless of system pressure changes. From wastewater aeration to pneumatic conveying, vacuum systems to biogas handling, roots blowers are the workhorses of industry.

Based on commissioning experience across hundreds of installations, roots blowers serve applications where constant flow is critical – and where other technologies fail. They handle dust, moisture, and debris that would destroy screw compressors. They maintain airflow as filters foul and diffusers clog. They deliver oil-free air for food and aquaculture.

This guide answers what is roots blower used for, with real-world applications across industries. Use it to understand where roots blowers excel – and where they don't.

Table of Contents

• What Is a Roots Blower?

• How Does a Roots Blower Work?

• Main Components

• Types of Roots Blowers

• Key Applications by Industry

• Advantages of Roots Blowers

• Common Problems and Troubleshooting

• Selection Guide

• Comparison With Alternatives

• Frequently Asked Questions

• Final Thoughts

What Is a Roots Blower?

A roots blower is a positive displacement rotary lobe machine that moves a fixed volume of air or gas per revolution. Two synchronized rotors (lobes) trap air at the inlet and push it out the discharge. No internal compression. No valves. Pressure is created by downstream system resistance.

Key characteristics:

• Constant volume – delivers same ACFM regardless of pressure (within range)

• No internal compression – air is discharged at system pressure

• Oil-free operation available (with proper seals)

• Simple construction – two rotors, four bearings, two gears

• Continuous duty – designed for 24/7 operation

Based on field data, roots blowers are used in over 80% of wastewater treatment plants for aeration. They are the standard for pneumatic conveying in cement, food, and chemical industries. They handle biogas, provide vacuum, and deliver combustion air.

How Does a Roots Blower Work?

Step 1 – Air intake. Motor turns drive shaft. Timing gears force both rotors to spin at identical speed in opposite directions. As a lobe passes the inlet port, the cavity opens to atmosphere. Air fills this space.

Step 2 – Trapping and transport. The rotor continues turning, sealing the cavity against the casing wall. The trapped air is carried toward the discharge port at inlet pressure.

Step 3 – Discharge and backflow. When the cavity reaches the discharge port, it opens to higher pressure. The rotor does not compress the air. Higher-pressure air from the discharge side backflows into the lobe cavity until pressures equalize. This takes milliseconds.

Step 4 – Pushing the volume. The rotor finishes rotation and pushes the volume out. The cycle repeats.

What this means for applications:
The blower delivers constant volume. Your downstream system determines pressure. If you need constant airflow as filters clog or diffusers foul, a roots blower is the right choice.

Main Components

Rotor (impeller). Traps and transports gas. Lifespan: 60,000–100,000 hours clean air. Failure: wear, corrosion, pitting.

Timing gears. Maintain rotor phase. Lifespan: matches blower life. Failure: wear, backlash increase.

Bearings. Support rotor loads. Lifespan: 40,000–50,000 hours. Failure: lubrication failure, contamination.

Casing. Enclosure and sealing surface. Lifespan: 20+ years. Failure: corrosion, erosion.

Shaft seals. Prevent oil migration. Lifespan: 8,000–10,000 hours. Failure: wear, hardening.

Types of Roots Blowers

Key Applications by Industry

Wastewater Treatment – The Largest Application

• Aeration basins need constant dissolved oxygen (2.0 mg/L minimum)

• Roots blowers maintain airflow as diffusers foul

• Typical pressure: 6–10 psig

• Flow: 500–5,000+ SCFM

• VFD control saves 25–35% energy

Pneumatic Conveying

• Moves bulk materials through pipelines

• Dilute phase: 8–12 psig, material suspended in air

• Dense phase: 15–20 psig, material as plugs

• Materials: cement, fly ash, plastic pellets, flour, grain

• Roots blowers provide constant flow – critical for keeping material suspended

Cement Plants

• Raw meal and fly ash are highly abrasive

• Hard-chrome rotors extend life to 24–36 months

• 2-micron filtration is mandatory

• Roots blowers handle dust that destroys screw compressors

Biogas Systems

• Landfill and digester gas: methane 50–70%, H2S 500–5,000 ppm

• Stainless steel rotors (316L) for corrosion resistance

• Explosion-proof motors required

• Pressure: 3–15 psig for upgrading, 15–20 psig for pipeline injection

Aquaculture

• Shrimp and fish ponds require 2–5 psig aeration

• Oil-free air is critical – fish are sensitive to oil

• Labyrinth seals prevent lubricant contamination

• VFD matches airflow to stocking density

Dust Collection

• Vacuum systems for baghouses and cartridge collectors

• Roots blowers handle dusty air better than vane pumps

• Vacuum: 8–15 inches Hg

• 2-micron filtration recommended for abrasive dust

Vacuum Systems

• Vacuum conveying, paper dewatering, packaging

• Roots blowers provide constant vacuum as system conditions change

• Vacuum: 5–18 inches Hg

• Tighter tip clearance required (0.05–0.10 mm)

Food Processing

• Pneumatic conveying of flour, sugar, starch

• Oil-free air mandatory – FDA compliance

• Stainless steel construction

• Carbon-graphite bearings for zero lubrication

Chemical Plants

• Solvent vapor recovery, tank blanketing

• Corrosive gases require stainless steel

• Explosion-proof motors for hazardous areas

• Gas-tight seals prevent leakage

Power Generation

• Combustion air for boilers

• Ash handling (pneumatic conveying)

• Flue gas treatment

• High temperature service (C4 bearings)

Steel Plants

• Combustion air for blast furnaces

• Pneumatic conveying of iron ore, coke, limestone

• Dust collection

• Hard-chrome rotors for abrasion resistance

Paper Mills

• Vacuum dewatering on paper machines

• Vacuum: 5–18 inches Hg

• Stainless steel rotors for corrosion resistance

• Moisture handling – condensate drains

Textile Mills

• Pneumatic conveying of fibers

• Vacuum on spinning and weaving machines

• Dusty, fiber-laden environment

• 5-micron filtration recommended

Water Treatment

• Air stripping of VOCs and H2S

• Oxidation of iron and manganese

• Pressure: 5–10 psig

• Oil-free air for potable water

Advantages of Roots Blowers

Flow stability. Constant ACFM from 2 psig to 12 psig. Centrifugal fans lose 30–40% of flow over the same pressure rise.

Mechanical simplicity. Two rotors, four bearings, two gears. Rebuild in eight hours.

Oil-free air. Labyrinth or lip seals keep oil out of the air stream. Discharge oil carryover below 1 ppm.

Debris tolerance. Small solids pass through without damage. Screw compressors would seize.

First cost advantage. 30–50% less than oil-free rotary screw compressors.

Dry running capability. Carbon-graphite bearing models run with no lubrication.

VFD compatibility. Excellent turndown (30–100%) for energy savings.

Common Problems and Troubleshooting

Selection Guide

Step 1 – Define application. Aeration, conveying, vacuum, biogas, etc.

Step 2 – Determine flow (ACFM). Correct SCFM to ACFM using altitude and temperature.

Step 3 – Determine pressure (psig or inches Hg). Add 15–20% margin for fouling.

Step 4 – Select type. Three-lobe direct-coupled is standard. High pressure for >15 psig. Vacuum type for suction.

Step 5 – Specify materials. Cast iron for clean air. Stainless for corrosive. Hard chrome for abrasive.

Step 6 – Specify seals. Lip seals for general. Labyrinth for oil-free. Gas-tight for biogas.

Step 7 – Calculate motor power. BHP = (ACFM × psig) / (229 × ηmechanical × ηmotor). Add 15–20% safety factor.

Comparison With Alternatives

When to choose roots blower:

• Constant flow required against varying pressure

• Dusty or dirty air

• Simple maintenance

• Moderate pressure (5–15 psig)

• Oil-free air required

When not to choose roots blower:

• High pressure (>15 psig) – consider screw compressor

• Clean, steady pressure, high efficiency – consider centrifugal fan

• Deep vacuum (>20 inches Hg) – consider liquid ring or vane pump

Frequently Asked Questions

1. What is a roots blower used for?
A roots blower is used for moving air and gas at low to medium pressure in industrial applications. Primary uses: wastewater aeration (supplying oxygen to bacteria), pneumatic conveying (moving materials through pipelines), vacuum systems (suction for conveying and packaging), biogas handling, and process air. It is chosen where constant airflow is required regardless of pressure changes.

2. What is the difference between a roots blower and a compressor?
A roots blower has no internal compression – it moves a fixed volume of air at constant flow. A compressor reduces volume, increasing pressure internally. Roots blowers are used for low-pressure applications (2–15 psig). Compressors are used for high pressure (>15 psig). Roots blowers are simpler, cheaper, and more debris-tolerant.

3. Is a roots blower the same as a centrifugal fan?
No. A roots blower is a positive displacement machine – it delivers constant volume regardless of pressure. A centrifugal fan is a dynamic machine – flow decreases as pressure rises. Roots blowers are used when constant flow is critical (aeration, conveying). Centrifugal fans are used for high flow at low pressure with steady conditions (ventilation).

4. Can a roots blower be used for vacuum?
Yes – roots blowers are used for vacuum applications. Vacuum type blowers operate with inlet below atmospheric pressure. Typical vacuum range: 5–18 inches Hg. Applications: vacuum conveying, paper dewatering, packaging, dust collection. Vacuum blowers have tighter tip clearance and vacuum-oriented seals.

5. What pressure can a roots blower achieve?
Standard three-lobe roots blowers: 2–15 psig. High-pressure designs: 10–25 psig. Best efficiency: 5–10 psig. Above 15 psig, efficiency drops and screw compressors become more efficient. Vacuum: 5–18 inches Hg.

6. Is a roots blower oil-free?
Roots blowers can be oil-free with proper seals. Standard lip seals can leak oil over time. For oil-free applications (food, pharma, aquaculture), specify labyrinth seals with buffer air or carbon-graphite bearings. These designs deliver zero oil in the air stream.

7. How long does a roots blower last?
With proper maintenance: bearings 40,000–50,000 hours (5–6 years). Rotors and timing gears 80,000–100,000 hours (10–12 years). Casing exceeds 20 years. Total lifespan: 15–20 years. Key factors: inlet filter maintenance, oil changes, diffuser cleaning (aeration).

8. What industries use roots blowers?
Roots blowers are used in wastewater treatment, cement plants, pneumatic conveying, biogas, aquaculture, food processing, chemical plants, power generation, steel plants, paper mills, textile mills, and water treatment. They are the standard for any application requiring constant, oil-free airflow at moderate pressure.

9. Why choose a roots blower over a screw compressor?
Lower first cost (30–50% less), higher debris tolerance (handles dust), simpler maintenance (in-house rebuild), and constant flow characteristic. Choose roots for pressures under 12 psig, dirty air, or where simple maintenance is critical. Choose screw for pressures above 15 psig, clean air, and efficiency priority.

10. Can roots blowers handle corrosive gases?
Yes – with stainless steel components. For biogas (H2S 500–5,000 ppm), specify 316L stainless rotors and corrosion-resistant timing gears. For chemical service with VOCs, specify explosion-proof motors and spark-resistant rotors. Standard cast iron fails in corrosive service.

11. Do roots blowers need silencers?
Yes – roots blowers generate significant noise (90–100 dBA) from pressure pulsation. Inlet and discharge silencers are required for noise compliance. Silencers reduce noise to 75–85 dBA. Without silencers, noise levels exceed OSHA and EU exposure limits.

12. Can roots blowers be used with VFD?
Yes – VFD is highly recommended for variable flow applications. Flow ∝ speed, power ∝ speed³. VFD saves 25–35% energy in variable flow applications. Specify inverter-duty motor. Payback 12–24 months typical.

13. What is the efficiency of a roots blower?
Three-lobe roots blowers: 72–78% efficiency at 5–10 psig. Drops to 68–74% at 12 psig and 65–72% at 15 psig. Best efficiency is at 5–10 psig. Twin-lobe: 65–72% at 8 psig.

14. Can roots blowers run continuously?
Yes – industrial roots blowers are designed for 24/7 continuous duty. Wastewater treatment plants run blowers 8,000+ hours annually. Continuous duty requires proper cooling, oil changes, and filter maintenance. With maintenance, lifespan is 15–20 years.

15. How do I size a roots blower for my application?
Calculate required SCFM from process requirements. Correct to ACFM using altitude and temperature: ACFM = SCFM × (14.7/Patm) × (T/520). Determine pressure at blower discharge. Add 15–20% margin for fouling. Calculate BHP = (ACFM × psig) / (229 × ηmechanical × ηmotor). Add 15–20% safety factor for motor. Select three-lobe direct-coupled as baseline. Consult manufacturer for verification.

Final Thoughts

After decades of specifying roots blowers, here is my practical advice:

The answer to "what is roots blower used for" is: constant airflow applications. Wastewater aeration is the largest application – roots blowers maintain airflow as diffusers foul. Pneumatic conveying relies on roots blowers to keep material suspended. Biogas, vacuum, dust collection, and process air all benefit from constant flow.

Choose roots blowers when: You need constant flow against varying pressure. Your air is dusty or dirty. You want simple, in-house maintenance. Your pressure is 5–15 psig. You need oil-free air.

Choose something else when: Your pressure exceeds 15 psig. Your air is clean and pressure is steady. You need deep vacuum (>20 inches Hg). Efficiency is your only criterion.

The bottom line. Roots blowers are the workhorses of industry – used wherever constant airflow is critical. They handle the toughest conditions: dust, moisture, debris, and continuous operation. Zhanggu and other manufacturers offer roots blowers for every application. Specify correctly, maintain regularly, and they will serve you for decades.