Gear Pumps

Pumps ·

Gear pumps are positive-displacement machines that move fluid by trapping it in the spaces between rotating gear teeth and the pump casing. They deliver a precise, consistent volumetric flow per revolution, making them the standard choice for hydraulic power systems, metering applications and the transfer of viscous oils, resins and polymers.

History

The concept of using intermeshing gear teeth to displace fluid was described by the German astronomer Johannes Kepler around 1604 in correspondence regarding water pump design — one of the earliest documented references to the gear pump principle. The first documented practical gear pump mechanism is attributed to Pappenheim in Germany in 1636. During the Industrial Revolution the design was refined for lubrication and hydraulic service in European and North American factories. In 1911 Viking Pump Company of Cedar Falls, Iowa became one of the first dedicated gear pump manufacturers in the United States, establishing the product standards and operating principles that remain in use across the industry today.

Operating Principle

Two meshing gears rotate in opposite directions inside a close-fitting casing. On the suction side the gear teeth disengage, creating expanding pockets that draw fluid in. The fluid is carried in the tooth spaces around the outside of the gears — it cannot pass back through the mesh — and is discharged on the pressure side as the teeth re-engage and reduce the pocket volume.

Gear Configurations

  • External gear: Two externally-toothed gears mesh together — standard design for hydraulics and oil transfer; higher pressure capability
  • Internal gear (gerotor): A small external gear rotates inside a larger internal gear — quieter, one moving part, suited to food and pharmaceutical applications; smoother flow
  • Helical gear: Angled teeth reduce noise and pulsation compared to spur gears; preferred for noise-sensitive installations

Key Technical Parameters

  • Flow rate (Q): 0.01 to 500 m³/h
  • Differential pressure: Up to 250 bar for external gear; up to 200 bar for internal gear
  • Viscosity range: 5 cSt to 100,000 cSt — performance improves with increasing viscosity as internal leakage (slippage) decreases
  • Speed: 100 to 3,600 RPM; higher speeds increase flow but reduce volumetric efficiency at elevated pressure
  • Temperature: Up to +250 °C with high-temperature seals and materials

Applications

  • Hydraulic power units for mobile and industrial machinery
  • Lubrication oil circulation in engines, turbines and compressors
  • Fuel oil burner supply in boilers and furnaces
  • Chemical dosing and metering at precise volumetric rates
  • Bitumen, asphalt and tar transfer in road construction
  • Resins, adhesives and polymer transfer in plastics processing
  • Confectionery — chocolate, caramel and jam dosing

Advantages

  • Constant, accurate flow per revolution — ideal for metering
  • Self-priming with suction lift capability up to 8 m
  • High pressure in a compact, lightweight package
  • Performance improves with increasing viscosity
  • Simple construction — only two moving parts in a standard external gear pump
  • Handles fluids with lubricating properties without additional bearing lubrication

Limitations

  • Not suitable for abrasive media — particles accelerate gear wear rapidly
  • Not suitable for solids or fibrous materials that cannot pass through tight gear mesh clearances
  • Shear forces between gear teeth can degrade shear-sensitive fluids such as emulsions
  • Flow pulsation increases with tooth pitch — helical gears mitigate this
  • Slippage (internal leakage) increases at low viscosities and high differential pressure — reduces volumetric efficiency
  • Reverse rotation requires pump redesign — standard pumps are unidirectional

Selection Criteria

  • Confirm fluid is free of abrasive particles — filtration upstream is mandatory
  • Measure viscosity at minimum and maximum operating temperature — gear pumps become less efficient at very low viscosity
  • Calculate required differential pressure — external gear for high pressure duty, gerotor for quiet, moderate-pressure service
  • Choose gear material: steel for petroleum and chemical service, stainless steel for food and pharmaceutical, PEEK or PTFE-coated for aggressive chemicals
  • Select shaft seal: lip seal for low-pressure clean service, mechanical seal for high pressure or hazardous fluids
  • Specify by displaced volume per revolution (cm³/rev) combined with speed range to meet the required flow rate

Top 10 Manufacturers

  • 1. Parker Hannifin / Hydraulics Division (USA) — ~14% global market share; mobile and industrial hydraulic gear pumps
  • 2. Bosch Rexroth AG (Germany) — ~12%; external and internal gear for mobile machinery
  • 3. IDEX / Viking Pump (USA) — ~11%; process and industrial internal gear pumps
  • 4. Eaton Corporation (Ireland / USA) — ~10%; heavy mobile hydraulics gear pumps
  • 5. Tuthill Pump Group (USA) — ~8%; transfer and metering gear pumps
  • 6. Maag Group (Switzerland) — ~6%; high-precision gear pumps for polymer and chemical
  • 7. Fluid-o-Tech srl (Italy) — ~6%; miniature gear pumps for espresso machines and precision cooling
  • 8. Oberdorfer Pumps / Envirogear (USA) — ~5%; sanitary and chemical internal gear
  • 9. Zenith Pumps (USA) — ~4%; precision metering gear for polymer extrusion lines
  • 10. Blackmer / PSG (USA) — ~4%; sliding vane and gear pumps for petroleum transfer