Although Roots blowers and Roots pumps belong to the same category of positive displacement rotor machinery and have similar structures (both using the dual rotor meshing principle), there are essential differences in design goals, performance parameters, and application scenarios. The following is a detailed comparative analysis of the two:
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**1、 Overview of Core Differences**
|* * Comparison item * * | * Roots blower * * | * Roots pump * *|
|------------------|-----------------------------|------------------------------|
|* * Core function * * | Gas transportation and pressurization | Liquid or high viscosity medium transportation|
|* * Design pressure * * | Low pressure (0.1~0.8 bar) | Medium low pressure (0.5~3 bar)|
|* * Medium type * * | Air/gas dominant | Liquid/slurry/high viscosity fluid|
|Sealing requirements * * | General mechanical seal | High pressure end mechanical seal+shaft seal system|
|* * Typical efficiency * * | 60~75 | 50~65 (greatly affected by viscosity)|
|* * Speed range * * | 500~3000 rpm | 200~1000 rpm (anti shear)|
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**2、 Detailed explanation of structural differences**
**1. Rotor design**
-Roots blower:
-Two leaf or three leaf involute rotor with straight teeth, with a large gap (0.1~0.3mm) to prevent thermal expansion and jamming.
-Material: cast iron (HT250) or aluminum alloy (lightweight design).
-Roots pump:
-Spiral rotor (2-4 head spiral) reduces liquid pulsation and shear failure.
-Material: Stainless steel (316L) or silicon carbide (wear-resistant and corrosion-resistant).
**2. Sealing system**
-Roots blower:
-Ordinary skeleton oil seal or labyrinth seal (with minimal impact of gas leakage).
-Roots pump:
-* * Double end mechanical seal * *+flushing system (to prevent liquid leakage).
-High voltage models are equipped with * * magnetic couplers * * (zero leakage).
**3. Shell and gap**
|* * Parameters * * | * Roots blower * * | * Roots pump * *|
|------------------|----------------------------|----------------------------|
|Shell wall thickness | 8-15mm (cast iron) | 12-25mm (stainless steel)|
|Rotor clearance | 0.15~0.4mm | 0.05~0.15mm (anti liquid reflux)|
|Import and export pressure difference | ≤ 0.8 bar | ≤ 3 bar (special design can reach 6 bar)|
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**3、 Comparison of working principles**
**Roots blower (gas conveying)**
1. The rotor rotates to form a closed cavity, pushing gas from the inlet to the outlet.
2. * * No internal compression * *, pressure is established by system resistance.
3. The airflow pulsation is obvious, and a muffler is required.
**Roots pump (liquid delivery)**
1. The spiral rotor forms a continuous sealed cavity, driving the axial flow of liquid.
2. * * Low shear design * * to avoid damaging the medium structure (such as lotion and mud).
3. It is necessary to prevent cavitation (NPSHr ≤ 3m).
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**4、 Differences in performance curves**
|* * Features * * | * Roots blower * * | * Roots pump * *|
|------------------|----------------------------|----------------------------|
|Flow pressure curve | Constant flow rate, pressure increases with resistance | Flow rate slightly decreases with increasing pressure|
|Viscosity effect | Almost no effect | Flow rate significantly decreases with increasing viscosity|
|Allow idling | Short time idling allowed | Strictly prohibit idling (dry friction damages the seal)|
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**5、 Application scenarios**
**Typical use of Roots blower**
-Sewage treatment aeration
-Pneumatic conveying (fly ash, grains)
-Vacuum packaging assistance
**Typical Applications of Roots Pump**
-Petroleum industry: heavy oil transportation
-Food industry: chocolate and syrup transfer
-Chemical industry: resin and adhesive measurement
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**6、 Selection precautions**
1. * * Medium characteristics * *:
-Gas selection fan, liquid/high viscosity selection pump.
2. * * Pressure demand * *:
-Priority should be given to Roots pumps when the pressure exceeds 0.8 bar.
3. * * Sealing grade * *:
-Dangerous liquids must use magnetic driven Roots pumps.
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**7、 Comparison of Maintenance Points**
|* * Project * * | * Roots blower * * | * Roots pump * *|
|------------------|----------------------------|----------------------------|
|Lubrication cycle | 2000 hours (gear oil) | 500 hours (medium resistant grease)|
|Key wear parts | rotor tip, bearings | mechanical seals, rotor surface|
|Shutdown protection | No special treatment required | Liquid needs to be emptied to prevent crystallization|
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**8、 Cost difference**
-* * Procurement cost * *: Roots pumps are 30-50 more expensive at the same flow rate (due to high material/sealing requirements).
-Operating costs: Roots pumps consume 10-20% more energy due to the influence of medium viscosity.
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**Summary**
-* * Essential difference * *: Roots blower is * * gas boosting equipment * *, Roots pump is * * volumetric liquid conveying equipment * *.
-* * Non interchangeable * *: Even if the structure is similar, unauthorized changes in usage may result in seal failure or a sudden drop in efficiency.
-* * Special model * *: There is a dual-purpose Roots machine for gas and liquid (customized design required).
When selecting, it is important to clarify the type of medium, viscosity, and pressure requirements, and refer to the manufacturer's technical manual for matching.
