1. The fundamental difference
Gear pumps are positive displacement. Each rotation transfers a fixed volume of fluid. Flow is proportional to speed and practically independent of pressure. They are ideal for viscous fluids because volumetric efficiency increases with viscosity.
Centrifugal pumps transfer kinetic energy to the fluid through an impeller. Flow depends on the pressure differential and viscosity. With viscous fluids, efficiency drops sharply. They are ideal for high flows of light fluids.
2. Side-by-side comparison — data from technical manuals
The table below compares the operating limits of the FBE (gear) and FBCN (centrifugal) series, extracted directly from their respective technical manuals.
| Parameter | FBE (Gear) | FBCN (Centrifugal) |
|---|---|---|
| Type | Positive displacement | Kinetic (impeller) |
| Max viscosity | Up to 100,000 SSU | Low-viscosity fluids |
| Max flow | Up to 390 m³/h | Up to 2,200 m³/h |
| Max pressure | Up to 16 kgf/cm² | Up to 20 bar (cast iron) |
| Head | Up to 220 m | Up to 138 m |
| Max temperature | -50°C to 350°C | -50°C to 260°C |
| Speed | Up to 1,750 rpm (direct) | Up to 3,500 rpm |
| Sizes | DN 1/8" to 6" | DN 25 to 300 mm |
| Construction | Helical gears | Back-pull-out, radial impeller |
| Maintenance | Front access to seal/packing | Remove bearing without disconnecting piping |
3. When to use a gear pump (FBE/FBEI)
A gear pump is the correct technical choice when the process involves:
- Viscous fluids above 500 SSU (oils, asphalt, molasses, resins, polymers, chocolate)
- Temperatures above 260°C (FBCN centrifugal limit) — the FBE operates up to 350°C with heating jacket
- Flow proportional to speed (dosing, metering, controlled transfer)
- Fluids that solidify at room temperature (CAP asphalt, paraffins) — CA variant with heating jacket
- Low pulsation is needed (internal gear FBEI has smoother flow than external gear)
4. When to use a centrifugal pump (FBCN/FBOT)
A centrifugal pump is the correct technical choice when the process involves:
- Low-viscosity fluids (water, solvents, process fluids) — peak efficiency below 100 SSU
- High flow rates (above 390 m³/h) — the FBCN handles up to 2,200 m³/h
- High speeds (3,500 rpm) with direct drive from standard electric motor
- Simplified maintenance is a priority — back-pull-out design allows removing the rotating assembly without disconnecting piping
- Thermal oil above 260°C — the FBOT series is a centrifugal pump specific to thermal oil up to 350°C, with mechanical seal in a cooled chamber
5. The gray zone: 100 to 500 SSU
In the 100 to 500 SSU range, both technologies can work. The decision depends on additional factors:
- If the required flow is high (above 100 m³/h), the centrifugal pump tends to be more efficient
- If flow accuracy is critical (dosing, custody transfer), the gear pump is preferable
- If there are suspended solids, the centrifugal pump is more tolerant (with S3 flushing seal)
- If the temperature exceeds 260°C, only FBE or FBOT are options
6. Summary: quick decision tree
Use this quick reference based on data from FB Bombas technical manuals:
- Viscosity > 500 SSU → Gear pump (FBE or FBEI)
- Viscosity < 100 SSU + flow > 100 m³/h → Centrifugal (FBCN)
- Thermal oil up to 260°C → Centrifugal (FBCN with proper seal)
- Thermal oil 260°C to 350°C → Specific centrifugal (FBOT)
- Asphalt, molasses, chocolate, resins → Gear pump (FBE or FBE-CA)
- Water, solvents, effluents → Centrifugal (FBCN)
- Low pulsation for dosing → Internal gear (FBEI)
