Centrifugal pumps are designed primarily for low-to-medium viscosity fluids (like water, oils, and light chemicals). As viscosity increases, pump performance declines due to higher frictional losses and reduced efficiency.
| Fluid Type | Viscosity (cP or mPa·s) | Suitability |
|---|---|---|
| Water, Thin Liquids | 1–10 cP | ✅ Excellent |
| Light Oils, Fuel | 10–100 cP | ✅ Good |
| Heavy Oils, Syrups | 100–500 cP | ⚠️ Limited |
| Molasses, Sludges | 500–1,000+ cP | ❌ Poor |
~500 cP: Centrifugal pumps start struggling.
>1,000 cP: Positive displacement pumps (gear, screw, diaphragm) are better.
Reduced Flow Rate
Thicker fluids move slower, decreasing flow capacity.
Lower Efficiency
More energy is lost to friction (impeller & casing).
Higher Power Demand
Motor load increases to overcome viscous drag.
Risk of Cavitation
High viscosity can restrict suction flow, lowering NPSHa.
If a centrifugal pump must handle viscous fluids:
✔ Slow Down the Pump (Use a VFD to reduce RPM).
✔ Increase Impeller Diameter (Boosts pressure capability).
✔ Use a Larger Pump (Higher flow area reduces shear).
✔ Preheat the Fluid (Reduces viscosity temporarily).
For fluids >500–1,000 cP, consider:
Gear Pumps (For oils, fuels).
Progressive Cavity Pumps (Slurries, pastes).
Diaphragm Pumps (Abrasive/chemical fluids).
Centrifugal pumps work best below 500 cP. For thicker fluids, reduce speed, modify the impeller, or switch to a positive displacement pump.
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