Although rotary fans (such as screw fans and slide fans) and Roots fans belong to the same category of positive displacement fans, there are significant differences in structure, working principle, and applicable scenarios. Here is a detailed comparison between the two:
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**1、 Comparison Table of Core Differences**
|* * Comparison item * * | * Roots blower * * | * Rotary blower (taking screw type as an example) * *|
|------------------|-------------------------------|-------------------------------|
|* * Working principle * * | Double rotor meshing conveying gas (without internal compression) | Screw meshing compressing gas (with internal compression)|
|* * Compression method * * | Volumetric conveying, pressure generated by system resistance | Internal compression, pressure determined by screw geometry|
|* * Efficiency * * | Low (50-70, worse at high pressure) | High (75-88, significant energy-saving advantage)|
|* * Noise * * | Large (80-95 dB, high-frequency pulsation) | Small (60-75 dB, smooth operation)|
|* * Maintenance complexity * * | Low (only requires adjustment of clearance) | High (requires regular replacement of screw seals)|
|* * Pressure range * * | Single stage ≤ 0.5 bar, dual stage ≤ 1.0 bar | 0.5~3 bar (some models can reach higher)|
|* * Typical Applications * * | Sewage Treatment, Pneumatic Conveying | Compressed Air, Vacuum Systems, Chemical Processes|
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**2、 Diagram of structural differences**
**1. Roots blower structure**
```
Air inlet → [rotor A] [rotor B] → exhaust outlet
↑
synchromesh gear
```
-* * Features * *:
-The two rotors are forced to synchronize through gears, with a fixed gap (0.1~0.4mm).
-No lubricating oil intervention (dry operation).
**2. Screw fan structure**
```
Air inlet → [male screw] [female screw] → exhaust outlet
↑
oil film seal
```
-* * Features * *:
-The screw engages with the spiral, and the gas is gradually compressed in the groove.
-Oil injection cooling and sealing are required (except for oil-free screws).
---
**3、 Performance Curve Comparison**
|* * Features * * | * Roots blower * * | * * Screw blower * *|
|------------------|-------------------------------|-------------------------------|
|* * Flow pressure curve * * | Vertical line (constant flow) | Gentle decrease (wide area)|
|* * Energy Efficiency Ratio * * | Better at low pressure, sharp drop at high pressure | Full pressure range|
|* * Pulsation * * | Significant (requires muffler) | Weak (continuous airflow)|
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**4、 Selection suggestions**
**Priority selection of Roots blower**
-Low pressure constant flow rate (if stable gas supply is required for sewage aeration).
-* * Dusty/humid gas * * (dirt resistant, simple structure).
-* * Limited budget * * (procurement costs are 30-50% lower).
**Prioritize the use of screw fans**
-Medium to high pressure demand (>0.8 bar compressed air system).
-Low noise environment (hospitals, laboratories).
-Long term energy-saving operation (electricity cost savings can offset high procurement costs).
---
**5、 Comparison of maintenance costs**
|* * Project * * | * Roots blower * * | * * Screw blower * *|
|----------------|--------------------------|--------------------------|
|* * Daily maintenance * * | Check gear oil, adjust clearance | Replace lubricating oil and air filter element|
|* * Overhaul cycle * * | 3-5 years (replacement of bearings/gears) | 2-3 years (refurbishment of screw coating)|
|* * Typical faults * * | Rotor collision, gear damage | Screw wear, oil circuit blockage|
---
**6、 Classic application scenarios**
-Roots blower:
-Aeration in sewage treatment plants (such as A2O process).
-Powder pneumatic conveying (cement, flour).
-* * Screw fan * *:
-Factory compressed air station (replacing piston engines).
-Food packaging vacuum system (oil-free model).
---
**7、 Clarification of Common Misconceptions**
1. * * "Rotary=Roots"**
-Error: Roots blower is a type of rotary type, but rotary type also includes screw type, slide type, etc.
2. "Roots blower is more durable"**
-One sidedness: Roots blower has a simple structure, but screw blower has a longer lifespan in high-pressure scenarios.
---
**Summary**
-Roots blower: Simple and reliable, suitable for low-pressure dirty environments, but with low energy efficiency and loud noise.
-* * Screw fan * *: energy-saving, suitable for medium and high pressure clean scenarios, but maintenance is complex and expensive.
Based on comprehensive selection of pressure requirements, gas properties, and operating costs. If specific model recommendations are needed, parameters such as flow rate and pressure can be provided for further analysis!
