Complete Roots Blower Selection Method (Industrial Practice Edition)

I. Core Principles of Selection

Roots blowers are positive displacement rotary blowers. Airflow and pressure rise (pressure) are the core parameters for determining the model; both are indispensable. The selection process follows the complete workflow of "first determine operating parameters, then calculate theoretical values, then apply operating condition corrections, and finally match the model + motor." Safety margins are reserved throughout the process to avoid overload, insufficient airflow, and equipment damage. This method is suitable for all scenarios including wastewater treatment, aquaculture, pneumatic conveying, desulfurization and denitrification, metallurgy and chemical industry, and aeration and oxygenation.

II. Preliminary Operating Condition Basic Data Collection

The following on-site data must be accurately collected before selection to avoid selection errors:

Application scenario: Aeration, pneumatic conveying, backwashing, vacuum suction, pressurized conveying

Conveying medium: Clean air, biogas, coal gas, dust-laden gas, corrosive gas

On-site environment: Altitude, ambient temperature, indoor/outdoor installation, noise limit, explosion-proof requirements

System conditions: Pipeline length, pipe diameter, number of elbows/valves, terminal equipment resistance, installation space dimensions

Operation requirements: Continuous operation/intermittent operation, airflow adjustable or not, power supply voltage

III. Core Parameter Definition and Calculation

(1) Airflow (Flow Rate) Selection Calculation

Parameter definition: Unit: m³/min (cubic meters per minute) or m³/h. Refers to the volume of gas delivered by the blower per unit time, which is the standard airflow under rated conditions.

Calculation principle: Based on the actual airflow required by the process, reserve a margin of 10%~25% to compensate for pipeline air leakage, resistance loss, and aging degradation. Additional margin is required for high-altitude and high-temperature environments.

Calculation formula: Actual selected airflow = Process required airflow × 1.1~1.25 (margin coefficient)

Industry standard airflow reference:

Small-scale aquaculture: 0.75~5 m³/min

Domestic sewage aeration: 5~30 m³/min

Industrial sewage, pneumatic conveying: 30~100 m³/min

Large-scale industrial conditions: above 100 m³/min

(2) Pressure Rise (Pressure) Selection Calculation

Parameter definition: Unit: kPa (kilopascal). Refers to the pressure difference between the blower outlet and inlet, i.e., the pressure required to overcome the total resistance of the pipeline + equipment. This is the second core parameter for selection. Overpressure operation is strictly prohibited.

Standard pressure level specifications:

Low pressure: 9.8~49 kPa

Medium pressure: 58.8~98 kPa

High pressure: 117.6~196 kPa

Two-stage high pressure: 196~245 kPa

Calculation principle:

Total pressure = Pipeline frictional resistance + Local resistance + Equipment resistance

Reserve 10% margin to avoid overload caused by pipeline blockage or increased resistance.

For vacuum suction conditions, convert based on the vacuum degree to the corresponding pressure.

(3) Motor Power Calculation

Standard calculation formula:
Motor power (kW) = [Airflow Q (m³/min) × Pressure rise P (kPa)] ÷ (60 × Blower efficiency η × 0.98) × 1.1~1.2 (motor margin)

Blower efficiency η: Typically 0.6~0.8

A 10%~20% safety margin must be reserved for the motor to prevent burnout during starting or full-load operation.

Simplified selection: Directly match standard power according to airflow + pressure rise using the manufacturer's data sheet; no complex calculation is required.

(4) Speed Selection

Low speed: Low noise, less wear, long life, larger size, higher cost – suitable for long-term continuous operation.

High speed: Smaller size, lower cost, higher noise, faster wear – suitable for small airflow, space-constrained scenarios.

Recommendation: Prefer medium to low speed models to extend service life and reduce operating and maintenance costs.

IV. Correction for Special Operating Conditions (Critical!)

High-altitude environment correction: Altitude > 1000m. Air is thin and density decreases. For every 1000m increase, airflow/pressure attenuates by about 10%. The airflow and motor power specifications need to be increased.

High-temperature environment correction: Ambient temperature > 40°C. Inlet air density decreases, power loss increases. The motor power needs to be increased, and the airflow margin raised.

Special medium correction:

Corrosive gas: Select 304/316 stainless steel material, corrosion-resistant seals.

Flammable/explosive gas: Standard explosion-proof motor, explosion-proof complete unit.

Dust-laden gas: Enhance inlet filtration, labyrinth seals, wear-resistant impeller.

Negative pressure/vacuum conditions: Select a vacuum-type Roots blower.

Noise requirement correction: For indoor, residential, or factory sensitive areas, select low-noise models + inlet silencer + discharge silencer + acoustic enclosure. Control noise below 85 dB.

V. Standardized Selection Steps (Perform in order)

Step 1: Determine the process required airflow and pressure rise
Accurately calculate the actual air demand. Do not blindly oversize or undersize. Determine the standard airflow and standard pressure rise.

Step 2: Add safety margins
Airflow × 1.1~1.25, pressure × 1.1 to obtain the final selection parameters.

Step 3: Secondary correction for high altitude / high temperature / special media
Adjust the corresponding parameters according to the on-site environment to determine the final selection values.

Step 4: Match the blower model
Use the manufacturer's model data sheet to match the Roots blower model, impeller specification, and port size that perfectly fit the airflow and pressure rise.

Step 5: Select the motor
Match the motor with corresponding power, protection rating, and explosion-proof rating to ensure no overload at full load.

Step 6: Confirm installation and accessories

Verify external dimensions, flange sizes, and installation method to fit the on-site space.

Select silencers, filters, acoustic enclosure, check valve, safety valve, and variable frequency drive (VFD).

For applications with large airflow fluctuations, a VFD is standard to save energy and precisely adjust airflow.

Step 7: Verify suitability for operating conditions
Confirm that materials, seals, explosion-proof rating, and protection rating fully match the on-site environment.

VI. Common Accessory Selection and Matching

Essential accessories: Inlet filter, inlet/discharge silencers, check valve, safety valve, vibration isolators.

Optional accessories: VFD control panel, acoustic enclosure, flexible connector, pressure gauge, flow meter.

Special accessories: Explosion-proof accessories, corrosion-resistant accessories, wear-resistant accessories.

VII. Key Selection Points for Different Applications

Wastewater treatment aeration: Medium to low pressure (58.8~98 kPa), continuous operation, low noise, ample airflow margin.

Pneumatic conveying: Medium to high pressure (98~196 kPa), wear-resistant impeller, anti-clogging, ample power margin.

Aquaculture aeration: Low pressure, small airflow, silent type, easy installation, stable operation.

Corrosive media in chemical industry: Full stainless steel material, mechanical seal/corrosion-resistant seal, explosion-proof model.

Negative pressure vacuum suction: Vacuum-type Roots blower, select according to vacuum degree, upgraded seals.

VIII. Selection Taboos and Pitfalls to Avoid

Never look only at airflow or only at pressure. Both are indispensable.

Avoid selecting without margins – this easily leads to overload, insufficient airflow, and equipment overheating.

High altitude and high temperature require parameter correction. Standard models will not work properly at high altitudes.

Do not operate beyond the rated pressure or speed – this will burn the motor and damage the blower housing.

Do not use standard carbon steel blowers for special media – risk of corrosion and leakage is extremely high.

Do not select a bare unit for noise-sensitive areas – noise reduction equipment must be included.

For long-term continuous operation, prioritize low-speed, high-power-margin, brand-name complete units.

A VFD enables stepless airflow adjustment and significant energy savings – its selection is recommended.

IX. Selection Acceptance Checklist

After finalizing the selection, verify the following information to ensure correctness:

Rated airflow and rated pressure rise meet process requirements.

Motor power, protection/explosion-proof rating are suitable for the site.

Materials and seals match the conveyed medium.

Installation dimensions and flange connections match the site.

Accessories are complete and meet operational, noise reduction, and safety requirements.

Suitability for site conditions such as altitude and temperature is confirmed.

Summary: Scientific and reasonable selection is the first step towards long-term stable operation of a Roots blower. Strictly following the sequence of operating condition data collection, parameter calculation, margin reservation, special condition correction, and model matching, while paying full attention to special conditions such as high altitude, high temperature, and corrosive media, can effectively avoid selection errors, extend equipment life, and reduce the total life cycle operating and maintenance costs.

Roots Blower product information

Web: http://www.greentechblower.com  (Group Web)  ‖  http://www.zqblower.cn  (Chinese)  ‖ http://www.ringblower.cn/ (Ring blower)  ‖  http://www.china-blower.com  (Roots Blower)