Progressive cavityGear pump FBE/FBEI
Progressive cavity or gear pump?
Two positive displacement technologies for viscous fluids. The real decision boundary is a single question: does the fluid carry solids or not.
TL;DR — Straight answer
Viscous fluid WITH solids or abrasives (sludge, mineral pulp, solid-laden pastes): progressive cavity pump — the rotor-stator pair tolerates particles that would destroy gears. CLEAN viscous fluid (oils, resins, asphalt, filtered molasses): gear pump — all-metal construction runs up to 350°C, has no elastomer stator to replace and keeps a compact footprint. Periodic stator replacement is the hidden cost that most often drives the migration from progressive cavity to gear pumps in clean service.
Option A
Progressive cavity
Helical rotor + elastomer stator
tolerates solids and abrasives
When to use
- Fluids with suspended solids or abrasives
- Shear-sensitive products (gentle pumping)
- Sludges, pulps and non-Newtonian pastes
- Temperature limited by the stator elastomer
Option B
Gear pump FBE/FBEI
All-metal · no wearing elastomer
up to 350°C
When to use
- Clean viscous fluids (up to 100,000 SSU)
- High temperature — asphalt, thermal oil (up to 350°C)
- Tight spaces: compact footprint vs long PC body
- Continuous duty with no periodic stator replacement
Side by side
| Criterion | Progressive cavity | Gear pump FBE/FBEI |
|---|---|---|
| Principle | Metal helical rotor turning inside an elastomer stator | Meshing metal gears (external FBE / internal FBEI) |
| Solids and abrasives | Tolerated — structural advantage of the rotor-stator pair | Not recommended — requires clean or filtered fluid |
| Maximum temperature | Limited by the elastomer: NBR ~90°C, EPDM ~150°C, specials ~180°C | Up to 350°C (all-metal construction, proper seal) |
| Dry running | Forbidden — rotor-stator contact damages the elastomer quickly | Not tolerated either — running without liquid destroys the seal film within minutes; self-priming starts with air in the line, but with a wetted chamber |
| Recurring wear item | Rotor-stator set (periodic replacement) | No elastomer in the fluid path; clearances checked at maintenance |
| Installed length | Long — helical stator plus rotor removal space | Compact — DN 1/8" to 6" in a short footprint |
| Product shear | Very low — gentle pumping of sensitive products | Low — suitable for stable oils, resins and polymers |
| Pulsation | Very low (continuous flow) | Low — FBEI reduces it further via the gear-within-gear principle |
| Design standard | ANSI/HI 3.1-3.5 (rotary pumps) | API 676 · ANSI/HI 3.1-3.5 |
Principle
Progressive cavity
Metal helical rotor turning inside an elastomer stator
Gear pump FBE/FBEI
Meshing metal gears (external FBE / internal FBEI)
Solids and abrasives
Progressive cavity
Tolerated — structural advantage of the rotor-stator pair
Gear pump FBE/FBEI
Not recommended — requires clean or filtered fluid
Maximum temperature
Progressive cavity
Limited by the elastomer: NBR ~90°C, EPDM ~150°C, specials ~180°C
Gear pump FBE/FBEI
Up to 350°C (all-metal construction, proper seal)
Dry running
Progressive cavity
Forbidden — rotor-stator contact damages the elastomer quickly
Gear pump FBE/FBEI
Not tolerated either — running without liquid destroys the seal film within minutes; self-priming starts with air in the line, but with a wetted chamber
Recurring wear item
Progressive cavity
Rotor-stator set (periodic replacement)
Gear pump FBE/FBEI
No elastomer in the fluid path; clearances checked at maintenance
Installed length
Progressive cavity
Long — helical stator plus rotor removal space
Gear pump FBE/FBEI
Compact — DN 1/8" to 6" in a short footprint
Product shear
Progressive cavity
Very low — gentle pumping of sensitive products
Gear pump FBE/FBEI
Low — suitable for stable oils, resins and polymers
Pulsation
Progressive cavity
Very low (continuous flow)
Gear pump FBE/FBEI
Low — FBEI reduces it further via the gear-within-gear principle
Design standard
Progressive cavity
ANSI/HI 3.1-3.5 (rotary pumps)
Gear pump FBE/FBEI
API 676 · ANSI/HI 3.1-3.5
How to decide in practice
Start with the fluid, not with the installed pump. If there are suspended solids, abrasives, or the product degrades under shear — wastewater sludge, mineral pulps, pastes with solid loading — the progressive cavity pump is the right technology and a gear pump should not replace it: a hard particle between metal teeth means accelerated wear or seizure. This boundary is honest and works both ways.
If the fluid is viscous and clean — lube oils, resins, filtered polymers, asphalt, molasses — the math flips. The structural weak point of the PC pump in that service is the elastomer stator: NBR typically runs up to ~90 °C and EPDM up to ~150 °C (special executions reach ~180 °C), dry running damages the elastomer quickly because rotor and stator work in permanent contact, and the rotor-stator set is a recurring maintenance item. A gear pump is all-metal: it operates up to 350 °C, starts with the suction line full of air without external priming (self-priming uses the previously wetted chamber as a seal) and has no wearing elastomer in the fluid path.
The third criterion is geometry and installation. A PC pump body is axially long — the helical stator needs length plus extra dismantling space to pull the rotor. The FBE gear series spans 1/8" to 6" in a short footprint, which solves cramped pump rooms and compact skids. A technical tie is broken by the real duty point: send fluid, viscosity at pumping temperature, flow and pressure to FB Bombas engineering — sizing will show whether the gear pump covers the service with margin.
Frequent technical questions
Can I replace a progressive cavity pump with a gear pump?
It depends on the fluid. If it is clean (no suspended solids) and the viscosity is within the series range — up to 100,000 SSU on the FBE — the swap usually eliminates periodic stator replacement and unlocks higher temperatures. If the fluid carries solids or is shear-sensitive, stay with the PC pump: that is its correct application.
Why does stator replacement weigh so much in PC pump cost?
The elastomer stator works in permanent contact with the rotor and is, by design, a wear item: abrasion, temperature and chemical attack reduce the pair's interference and the pump loses flow until the set must be replaced. In clean, hot service this cycle shortens — exactly the scenario where an all-metal gear pump runs with no equivalent item.
Which of the two accepts higher temperature?
The gear pump. The PC pump limit is the stator elastomer — typically ~90 °C with NBR and ~150 °C with EPDM, with special executions around ~180 °C. The all-metal FBE series handles fluids up to 350 °C with the proper mechanical seal and materials, covering asphalt and thermal oil.
And for low-pulsation dosing, which one?
Both technologies have low pulsation. With clean fluid, the FBEI (internal gear) delivers continuous flow via the equidistant seal between teeth and an integrated relief valve — with the advantage of having no elastomer stator. With particle-laden or shear-sensitive fluid, the PC pump remains the technically correct choice.
Still undecided?
The FB application engineer reviews your process condition — fluid, temperature, flow, viscosity — and points to the right series.