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Rotary Gear Pump | 2 Types of Rotary Gear Pump | Why External Gear Pump Had Been So Popular Till Now? | The Biggest Trends in Internal Gear Pump

Rotary Gear Pump

Because of their high capacity, long service life, and low acquisition and repair costs, rotary gear pumps are commonly used in modern hydraulic systems. High operating pressures, excellent volumetric and mechanical performance, and lower noise levels have mostly been achieved thanks to product growth in a rotary gear pumps.

01-Internal and external gear pump - internal gear pump design - hydraulic internal gear pump-rotary gear pump

Because of its flexibility and usability in design and manufacturing, the Rotary gear pump is receiving significant use and popularity for automotive oil and fuel delivery. The rotary gear pump has high volumetric efficiency and pumping operation that is smooth and steady. They also deal in a wide variety of fluid viscosities.

01-internal gear pump, rotary gear oil pump, rotary gear pump

Rotary gear pumps are categorized in a number of ways based on the type of their rotating element. They are:

  1. Rotary External Gear Pump
  2. Rotary Internal Gear Pump

Introduction to Pump

The pump is the hydraulic system’s epicenter. A hydraulic pump, like the heart in the human body, creates flow by transferring fluids in an area with an unfavorable pressure gradient. Pumps are usually divided into two groups:

  1. Positive displacement pumps
  2. Kinetic pumps

Rotary Gear Pump Design

Output Flow (Q) LPM = (cm3/r * RPM)/1000

Input Power (P) kW =(LPM * bar) / 600

Output Power (P) kW = (N-m * RPM)/9549

Shaft Torque (M) N-m = (cm3/r * bar)/62.8

Shaft Speed (n) RPM = (1000 * LPM) / cm3/r


Volumetric efficiency η (volume) = (Output flow actual / Output flow theoretical)

Mechanical efficiency η (Mechanical) = (Shaft torque theoretical / Shaft torque actual)

Total Efficiency η = η (volume) * η (Mechanical)

Rotary External Gear Pump

Positive displacement pumps, such as gear, vane, and piston pumps, are seen in all fluid power systems.  Amongst these, Rotary gear pumps are the most common type. The pump gets its name from the fact that it has two gears that are either side by side or external to each other. A gear pump is a high-precision unit with pretty stringent fits and tolerances limits that can withstand high differential pressures.

The series of meshing teeth on the suction side of this pump tends to separate; as a result of the separation of teeth on the suction side, vacuum gaps form, and ambient pressure pushes the liquid into the suction side, filling the gap between the teeth.

The liquid is held around and pushed out as the teeth of the two gears mesh. Since the meshing of teeth during rotation creates a seal that divides the entry and discharge sections of the secondary cavity, the liquid occupying the gaps between the two neighboring teeth revolves with them and is pulled outward through the discharge opening.

Working Principle of Rotary External Gear pump

The external gear pump operates on the principle that a motor-driven drive gear rotates an idler gear in the opposite direction. The liquid trapped in the gear teeth spaces between the housing bore and the outside of the gears is moved from the inlet side to the outlet side of the pump when the gears spin.

Working Operation of Rotary External Gear Pump

The hydraulic vacuum force provided by the pump pulls fluid into the pump, or it is pushed into the pump by gravity or a charge pump. A charge pump is typically only used for extremely high viscosities or extremely high flow rates.

01-external gear rotary gear pumps-rotary gear oil pump-rotary gear pump

After that, the fluid is circulated between the teeth of the gears. The fluid is pulled out of the space between the teeth as the gears begin to mesh. This mechanical force is capable of producing a great deal of hydraulic pressure.

01-rotary gear pump with motor-rotary gear oil pump-rotary gear pump

Rotary Internal Gear Pump

An internally cut rotor meshes with an externally cut gear idler (driven gear)  in these working operations. To keep liquid from flowing back to the pump’s suction line, a crescent-shaped partition may be used.

The power is transmitted to the rotor and then passed to the idler gear, which meshes with it. A partial vacuum is created when the teeth emerge from the mesh due to an increase in size. Under atmospheric air pressure, the liquid is squeezed into the vacuum and stays between the teeth of the rotor and idler until the teeth mesh, forcing the liquid out of these spaces and out of the pump.

01-internal gear pump working - crescent gear pump - rotary gear pump with motor

The teeth of the internal gear and idler gear split at the suction port and mesh again at the discharge port, as seen in the cross-sectional view.

The rotor and idler gears create a shield between the portions in position A, and the idler gear withdraws from the rotor in position B, revealing a suction side gap to be filled with liquid.

The gaps between the rotor and idler gears are fully filled at position C. The rotor and idler gears come together at position D, forcing the liquid outward through the discharge gap. The gear pump generally provides liquid at a right angle to the gear axis.

Most of these pumps are commonly used to supply pressurized oils up to 10 bar, and lubricate them in internal combustion engines, turbines, motors, and so on. Due to their small clearance level between the gears and the pump case certain pump models are not ideal for handling abrasives.

Advantages of Rotary Gear Pump

Disadvantages of Rotary Gear Pump

  • Four bushings in the liquid area
  • No solids allowed.
  • Fixed end clearances

Application of Rotary Gear pump

  • Different fuel and lube oils
  • Chemical and polymer additive measurements
  • Mixing and blending chemical products
  • Hydraulic applications in industrial and mobile devices (log splitters, lifts, etc.)
  • Caustic resistance and acids
  • Applications for low-volume transfer

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