Internal gear pumps
An internal gear pump uses one external rotor with internal teeth that mesh with a smaller idler gear inside it. A crescent-shaped partition separates suction from discharge as the rotor turns.
Compared with external gear:
| Property | External gear | Internal gear |
|---|---|---|
| Flow pulsation | Higher (~3-5%) | Lower (~1-2%) |
| Shear on fluid | Higher | Lower |
| Self-priming | Yes | Yes |
| Mechanical complexity | Simpler | More parts (idler, crescent) |
| Typical max viscosity | ~100.000 cSt | ~500.000 cSt |
| Best for | Bulk transfer, fuel, asphalt | Shear-sensitive viscous fluids |
The lower pulsation and gentler shear make internal gear the right pick when the fluid is fragile (latex, gel coats, chocolate, certain pharma intermediates) or when downstream equipment is pulsation-sensitive (spray nozzles, coating heads, calenders).
What FB Bombas builds
Our FBEI internal gear line comprises 10 official models across three configurations:
- Compact (Fig. 11): GG1, HJ12, HL12 — sizes 1” to 1½”
- With relief valve (Fig. 8): HL12, KK2, LQ21, LS3, M4 — sizes 1½” to 4”
- Heavy-duty 3” (Fig. 12): AS3, AK3, AL3 — reinforced 3” line
Sizes covered: 1” through 4”. Per the official FBEI manual (MAN001-10), performance specifications — flow, pressure, rotation — are determined application-by-application by FB Bombas application engineering rather than published as a fixed envelope. Request a duty- point quotation through Assistência Técnica (+55 11 4898-9211) for any specific service.
Sizing rule of thumb
For viscous fluids, run internal gear pumps slow. As a starting point:
| Viscosity (cSt) | Max recommended speed |
|---|---|
| 1 to 50 | Catalog rated speed |
| 50 to 500 | 80% of rated |
| 500 to 5.000 | 60% of rated |
| 5.000 to 50.000 | 40% of rated |
| > 50.000 | 25-30% of rated |
Speed reduction trades flow for the time fluid needs to fill the pump chambers — without this, the pump cavitates internally and flow drops far below rated.
Further reading
References
- API 676-2017 — Positive Displacement Pumps — Rotary.
- Hydraulic Institute — ANSI/HI 3.6-2016 Rotary Pump Tests.