Complete Technical GuideInternal Gear Pump
Complete technical guide on internal gear pumps: crescent principle, advantages over external gear, applications for sensitive fluids and how to specify.
What is an internal gear pump?
An internal gear pump uses an inner rotor (drive gear) spinning inside an outer ring gear, separated by a fixed crescent. This arrangement creates pumping chambers that transport fluid with very low pulsation and quiet operation. FB Bombas' FBEI Series handles fluids from 1 to over 1,000,000 cP.
How does the crescent principle work?
The crescent is a fixed separator positioned between the rotor and the ring gear. It hermetically isolates the suction chamber from the discharge chamber, preventing backflow and ensuring flow direction. Fluid is trapped between the teeth and the crescent surface, transported by positive displacement to the outlet.
Difference between internal and external gear pumps?
In external gear (FBE Series), two identical gears rotate in opposite directions — robust design for high pressure up to 22 kgf/cm². In internal (FBEI Series), the rotor spins inside the ring with a crescent separator — quieter operation, lower pulsation, ideal for shear-sensitive products like chocolate, adhesives and paints.
Can the FBEI operate with hot fluids?
Yes. The FBEI Series can be supplied with an integrated heating jacket that maintains fluid temperature during operation. The jacket supports steam up to 185°C or thermal fluid up to 232°C. The FBEI-LS (Large Size) version with integrated gear reducer handles heavy applications with asphalt and bitumen at high temperatures.
What Is an Internal Gear Pump?
Crescent principle and smooth positive displacement
The internal gear pump uses a rotor with external teeth that spins inside a ring with internal teeth. Between them, a fixed crescent-shaped element isolates the suction chamber from the discharge chamber. Fluid is captured between the teeth and crescent and transported by positive displacement with minimal pulsation.
This technology offers exceptionally quiet operation and smooth flow, making it ideal for shear-sensitive products such as chocolate, adhesives, paints and pharmaceuticals. The FB Bombas FBEI series includes an integrated relief valve, heating jacket option and FBEI-LS heavy-duty version with gearbox.
Quietest operation on the market
Integrated relief valve for overpressure protection
Heating jacket (steam up to 185°C / thermal up to 232°C)
FBEI-LS heavy-duty version with gearbox for demanding applications
How Does It Work?
4-phase pumping cycle with crescent separator
Suction
The rotor is driven by the shaft and meshes with the idler ring. In the disengagement zone, volume expands creating partial vacuum that draws fluid.
Crescent Isolation
The crescent-shaped separator hermetically isolates the suction from discharge chamber, preventing backflow and ensuring flow direction.
Volumetric Transfer
Fluid trapped between teeth and crescent is carried from suction to discharge by positive displacement — constant volume per revolution.
Smooth Discharge
In the re-meshing zone, volume decreases forcing fluid out with minimal pulsation and no significant product shear.
Internal vs. External
When to choose each gear type
| Criteria | Internal (FBEI) | External (FBE) |
|---|---|---|
| Pulsation | Minimal | Moderate |
| Noise | Very low | Moderate |
| Shear | Very low | Low |
| Max pressure | 16 bar | 22 kgf/cm² |
| Max flow | 600 m³/h | 6,500 L/min |
| Ideal for | Chocolate, paints, adhesives | Oils, asphalt, chemicals |
Internal Gear Advantages
Why choose internal gear for sensitive fluids
Quiet Operation
Low noise and vibration, ideal for environments with noise restrictions.
Minimal Pulsation
Near-laminar flow without pressure spikes. No pulsation dampeners needed.
Wide Viscosity Range
From light fluids to extremely high viscosity. Optional heating jacket for temperature.
Relief Valve
Integrated overpressure protection. Safety without external devices.
Self-Priming
Draws fluid without foot valve or auxiliary priming. Simplified installation.
Reversible
Flow reversal by reversing rotation. Flexibility for loading and unloading.
Industrial Applications
Sectors that use internal gear pumps
Food Industry
Chocolate, molasses, vegetable oils
Paints & Coatings
Paints, varnishes, pigments
Adhesives
Hot-melt, PVA, sealants
Pharmaceutical
Emulsions, creams, viscous bases
Petrochemical
Oils and petroleum derivatives
Oils & Lubricants
Lubricants, hydraulic oils
Asphalt
Bitumen, emulsions (FBEI-LS)
Cosmetics
Creams, lotions, soaps
How to Specify
Essential data for selecting the ideal FBEI
Fluid Type
Name, composition, solids presence and chemical compatibility.
Viscosity
Viscosity at pumping temperature (cP or cSt). Internal gear excels at high viscosity.
Flow & Pressure
Desired flow rate and differential pressure. Defines FBEI model and required speed.
Temperature
Defines heating jacket need, seal type and construction materials.
Seal Type
Mechanical seal or packing according to application, temperature and fluid characteristics.
Drive System
Direct electric motor or speed reducer (FBEI-LS for heavy-duty and high torque).
Frequently Asked Questions
What is an internal gear pump?
Uses an internal rotor inside a ring, separated by a fixed crescent. Transports fluids with very low pulsation and quiet operation — ideal for shear-sensitive products.
What is the difference from external gear?
Internal (FBEI) has quieter operation, lower pulsation and less shear. External (FBE) supports higher pressures and is more versatile for general viscous fluid applications.
Does the FBEI have a relief valve?
Yes, all FBEI pumps have an integrated relief valve that protects against overpressure without external devices.
Can it operate with hot fluids?
Yes, available with heating jacket: steam up to 185°C and thermal fluid up to 232°C. The FBEI-LS version handles heavy-duty high-temperature applications.
What is the FBEI-LS?
The heavy-duty version of the FBEI, with speed reducer drive for high torque at low speeds. Ideal for asphalt, bitumen and heavy oils in large volumes.
What fluids is it suitable for?
Chocolate, molasses, hot-melt adhesives, resins, paints, varnishes, lubricating oils, hydraulic oils, bitumen, polymers and pharmaceuticals. Viscosity from 1 to 1,000,000 cP.
Can I replace my current internal gear pump with an FBEI?
Yes. The FBEI Series covers the same technical segment as internal gear pumps from Viking, Maag, Tuthill, Hayward Gordon and RZR Bombas Positivas, with connection compatibility and sizing by the application engineering team. 10 catalogued models from 1" to 4" + FBEI-LS engineered-to-order for large capacities. Integrated relief valve, optional heating jacket, API 676 compliance. Manufactured in Cabreúva-SP since 1944, CRCC Petrobras qualified supplier — Family 6 (Rotating Equipment).
Companies that Trust FB Bombas
80+ years of excellence in internal gear pumps
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