**Deep analysis of the working principle of the two blade Roots fan**
**1、 Core structure composition**
1. * * Rotor system**
-Composed of two involute impellers arranged in parallel, the impellers usually form an "∞" shape (see Figure 1)
-Control of impeller clearance:
-Radial clearance: 0.15~0.30mm
-Axial clearance: 0.20~0.40mm
2. * * Transmission mechanism**
-Synchronous gear (precision level ISO 5-6) forced drive ensures non-contact meshing of the impeller
-The speed ratio is fixed at 1:1, and the steering is opposite (as indicated by the arrow in Figure 2)
3. * * Sealing system**
-Maze seal (low-pressure type) or mechanical seal (high-pressure type)
-Typical leakage rate:<3 (at rated pressure)
**2、 Principle of Gas Transport**
1. * * Work cycle decomposition * * (with 180 ° as one cycle)
|Phase angle | Left cavity status | Right cavity status|
|--------|--------------------|--------------------|
|0 ° | Inhalation completed | Exhaust started|
|90 ° | Gas enclosed transportation | Exhaust completed|
|180 ° | Exhaust begins | New intake begins|
2. * * Volume change characteristics**
-Theoretical displacement formula:
\[
V_g = (\pi R^2 - 2 \times A_{lobe}) \times L
\]
(R: impeller radius, A： Single leaf cross-sectional area, L： Impeller length)
-Example: When D=300mm impeller and L=400mm, Vg≈0.025m3/r
**3、 Performance Comparison with Three Leaf Type**
|* * Parameter * * | Two leaf type | Three leaf type|
|------------------|----------------------|----------------------|
|Pulsation rate | 12~15 | 5~8|
|Speed | 3500rpm | 2500rpm|
|Applicable pressure | ≤ 98kPa | ≤ 196kPa|
|Typical Applications | Vacuum Adsorption, Material Transport | Wastewater Treatment, Chemical Gas|
**4、 Calculation of key design parameters**
1. Calculation of instantaneous flow pulsation**
\[
Q_{instant} = V_g \times \omega \times [1 + \frac{r} {R}cos (2\theta)]
\]
(ω: angular velocity, r： Eccentricity of impeller
2. * * Capacity efficiency correction**
\[
\eta_v = 1 - \frac{C \times \Delta P}{\mu \times n}
\]
(C: Gap coefficient, μ： Gas viscosity
**5、 Typical Failure Modes**
1. Impeller collision**
-Feature: Periodic metal tapping sound
-Reason: Bearing wear leads to clearance exceeding tolerance (>0.5mm)
2. * * Gas reflux**
-Phenomenon: Abnormal increase in outlet temperature (Δ T>30K)
-Solution: Replace high-precision synchronous gear (backlash<0.05mm)
**6、 Selection calculation example**
**Working condition requirements * *:
-Transport air volume 8m3/min
-Pressure 58kPa
-Continuous operation
**Calculation steps * *:
1. Choose a two bladed design (suitable for pulsating scenes)
2. Calculate theoretical displacement:
\[
V_g = \frac{Q}{n \times 60 \times \eta_v} = \frac{8}{1450 \times 60 \times 0.88} ≈ 0.00104 \, \text{m3/r}
\]
3. Selection results:
-Model: ER-150
-Impeller size: D=150mm，L=200mm
-Supporting motor: 11kW
**7、 Technological progress**
1. Twisted blade rotor design (such as patent)
-Reduce the pulsation rate to below 3
-Noise reduction of 8-10 dB (A)
2. * * Composite coating technology**
-Spray polytetrafluoroethylene (PTFE) on the surface of the impeller
-Wear resistance life increased by 3-5 times
Attachment: * * Three dimensional flow field simulation diagram of a two blade Roots fan * * (CFD analysis shows that the high-pressure zone is concentrated at a 45 ° position on the exhaust side)
If specific performance curves or customized calculation tables are required, detailed operating parameters can be provided for further analysis.
