The * * pressure * * and * * air volume * * of Roots blower are its core performance parameters, which are interrelated but influenced by different factors. The following is a detailed analysis and selection operation guide:
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**1、 The essential relationship between pressure and air volume**
1. * * Pressure (P)**
-Definition: The static pressure difference between the outlet and inlet of a fan (unit: kPa、Bar、mmHO）。
-* * Determining factor * *: determined by the system back pressure * * (pipeline, valve, equipment resistance), and the fan itself does not generate pressure.
-Allowable values: Single stage ≤ 0.8 Bar, double stage ≤ 1.4 Bar (overpressure can damage the rotor).
2. * * Airflow (Q)**
-Definition: The volume of gas transported per unit time (unit: m3/min or m3/h).
-* * Determining factors * *: speed, rotor volume, and clearance leakage.
3. * * Key formulas**
\[
Q = V \cdot n \cdot \eta_v
\]
-(V): Rotor displacement per revolution (m3/r)
-(n): Speed (rpm)
-(\ eta-v \): Volume efficiency (70-85 for two leaves, 80-90 for three leaves).
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**2、 Interpretation of Performance Curve**
The air volume pressure curve of a typical Roots blower is as follows:
```plaintext
Airflow (Q)
↑
|_________
| ↘
| ↘ When the pressure increases, the air volume slightly decreases due to leakage
|_____________→ Pressure (P)
```
-* * Curve characteristics * *:
-The pressure is determined by the system, and the air volume is basically constant (based on the principle of displacement).
-The actual air volume slightly decreases with increasing pressure (internal leakage increases).
---
**3、 Selection and matching steps**
1. * * Determine system requirements**
-* * Calculate system resistance * *:
Including pipeline friction loss, local resistance (bends, valves), and terminal equipment pressure loss.
**Example * *:
-Sewage treatment aeration: water depth of 5m → required pressure ≥ 49 kPa (5 mHO).
-Pneumatic conveying: Pipeline pressure loss+separator resistance ≈ 68.6 kPa.
-* * Determine the required air volume * *:
**Example * *: The oxygen demand of the aeration tank is 20 m3/min.
2. * * Select fan parameters**
-* * Pressure margin * *: Selection pressure=system resistance x 1.1 (coefficient).
-Air volume matching: Select rated air volume ≥ required value (considering altitude and temperature correction).
3. * * Reference Selection Table**
|* * Required Parameters * * | * * Recommended Model * * | * * Motor Power * * | * * Applicable Scenarios * *|
|--------------------|--------------------|--------------|--------------------|
| Q=5 m3/min, P=49 kPa | -50 | 7.5 kW | Sewage treatment|
| Q=15 m3/min, P=78.4 kPa | -100 | 22 kW | High pressure pneumatic conveying|
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**4、 Methods for adjusting pressure and air volume**
1. * * Adjust pressure**
-* * Increase pressure * *: Close the outlet valve (↑ resistance → ↑ pressure).
-* * Reduce pressure * *: Open the valve or clean the pipeline blockage (↓ resistance → ↓ pressure).
**Do not increase pressure by increasing the rotational speed!
2. * * Adjust the air volume**
-* * Increase air volume * *:
-Increase the speed (requires motor power support, \ (Q \ propto n \)).
-Replace the large displacement rotor (requiring equipment modification).
-* * Reduce air volume * *:
-Reduce the speed (variable frequency control).
-Partial gas reflux by bypass (high energy consumption).
---
**5、 Frequently Asked Questions and Answers**
Q1： Why does the pressure meet the standard but the air volume is insufficient?
-* * Reason * *:
-The inlet filter is clogged (↑ intake resistance).
-Rotor wear (↑ internal leakage).
-The speed has not reached the rated value (belt slippage/insufficient voltage).
Q2： Can the same fan simultaneously meet high pressure and high air volume?
-* * Cannot * *! The power formula for Roots blower:
\[
N \propto Q \cdot P
\]
High pressure and large air volume require power, usually requiring separate design (such as two-stage series connection).
---
**6、 Operation precautions**
1. * * Valve must be installed * *: Set pressure=rated pressure × 1.1.
2. It is strictly prohibited to start without load: Before starting, fully open the valve and gradually adjust it.
3. * * Monitoring instruments * *:
-Pressure gauge (at the outlet flange).
-Flow meter (requiring temperature and pressure compensation).
---
**7、 Unit conversion**
|* * Unit * * | * * Conversion Relationship * *|
|---------------|---------------------------|
| 1 Bar = 100 kPa = 10.2 mHO |
| 1 m3/min = 60 m3/h |
| 1 kW = 1.36 HP |
---
**Summary**
-The pressure is determined by the system, and resistance needs to be calculated when selecting.
-The air volume is determined by the speed and rotor design, and the adjustment should take into account efficiency.
-* * Prioritize choosing a three blade fan * *: Under the same parameters, it has an efficiency 10-20 higher than a two blade fan.
If you need the performance curve of a specific model, please provide the air volume, pressure requirements, or original fan nameplate parameters!
