Category: Hydraulics and pneumatics

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 rotary gear pump.

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 a 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 categorised 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 epicentre. A hydraulic pump, like the heart in the human body, creates flow by transferring fluids in an area with an unfavourable 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. The gear pump is a high-precision unit with pretty stringent fits and tolerances limits that can withstand high differential pressures.

01 external gear rotary gear pumps rotary gear oil pump rotary gear pump Hydraulics and pneumatics Hydraulics and pneumatics Rotary Gear pump

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 rotating creates a seal that divides the entry and discharge sections of the secondary cavity, the liquid occupying the gaps between the two neighbouring 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.

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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.

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Rotary Internal Gear Pump

An internally cut rotor meshes with an externally cut gear idler (driven gear)  in these working operation. 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, 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 full 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 pump are commonly used to supply pressurised oils up to 10 bar, 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

  • High Speed
  • High pressure
  • No overlapping loads for the bearing
  • Relatively silent operation
  • The design is suitable for a wide range of materials

Disadvantages of Rotary Gear Pump

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

Application of Rotary Gear pump

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

Rotary Pump | 2 Types Of Positive Displacement Pump | Two Stage Rotary Vane Vacuum Pump

What is a Rotary Pump?

Rotary pumps are positive displacement pumps, which mean they pump a fixed amount of liquid after each revolution and are mostly used to treat viscous fluids. Regardless of the resistance to which the pump is pushing, a fixed amount of fluid is pushed with each revolution of the pump. It self-primes and maintains a nearly constant delivered power independent of pressure.

In terms of numbers, rotary pumps are the second most common kind of pump. They are also the second most cost-effective choice after centrifugal pumps.

01-types of positive displacement pumps-vane type vacuum pump-rotary screw pump-rotary lobe pump-rotary gear pump-rotary piston pump

Functions of Rotary Pumps

They can work on fluids that have a very high viscosity. However, as viscosity rises above a certain threshold, the most effective speed decreases. This is determined by clearance and shear action. The clearance is usually opened up by the production company with high viscosity fluids to minimise power consumption and retain low shear effects on the component.

Their capacities vary with speed but their effect on the slip in the low viscosity ranges is somewhat impacted by pressure but this effect tends to be reduced to a point as the viscosity increases.

Rotary Pump Parts

A fixed case comprising gears, cams, vanes, screws, plungers or related components, which are actuated by a rotation of the driving shaft, which are some of the types of the rotary pump.


Normally, rotary pumps are driven by electric motors, geared motors or motor belt drives. Only a steam turbine and in extremely unusual circumstances an internal combustion engine drive a rotary pump.

Instrumentation and control

Capacity regulation is achieved either by changing the pump speed or by recirculating a part of the discharge. The recirculation of fluid is a typical control mechanism, since rotary pumps are mostly powered with electric drives at a constant speed.


To safeguard rotary pumps from exposure to foreign materials, a continuous suction strainers should be mounted. This extends to most rotary pump projects except in comparatively clean plants where initial costs do not warrant a strainer to cover the pump.

A dirty or clogged strainer can affect the pump by raising the friction loss in the suction piping.

Rotary pump design

These pumps have been developed to minimise leakage from the discharge side to the suction side with very narrow gaps between their revolving and fixed sections. As they run at comparatively slow speeds, they are vulnerable to corrosion and unnecessary wear at higher speeds, which lead to greater clearances and lower pumping power.

Features of Rotary Pumps

• Adapted to transmit viscous liquids and liquid slurry (screw pumps)

• Movement of pulse less metering (gear pumps)

• Easy to use and maintain (rotary pumps, lube pumps)

• Ability to move highly viscous fluids and solids (hose pumps)

Types of Rotary pumps

Rotary pumps are broadly classified based on the type of their rotating element.

  1. Gear type pump
    1. External gear pump
    1. Internal gear pump
  2. Vane type pump
  3. Screw pump
  4. Lobular pump
  5. Cam and piston pumps

Internal Gear pumps

Internal gear pumps carry fluid from the inlet to the outlet ports between the gear teeth. On a stationary pin, the outer gear (rotor) drives the inner or idler gear. When the gears emerge from the mesh, voids form, and liquid flows into the cavities. The gear transmissions return to a mesh, reducing the volume and forcing the liquid out of the port of discharge. Liquid cannot flow backwards from the outlet to the inlet port because of the crescent.

01 Rotary internal gear pump Hydraulics and pneumatics Hydraulics and pneumatics Rotary pump

External Gear Pumps

Gears that come in and out of mesh are often seen in external gear pumps. Water runs towards the pump as the teeth emerge from the mesh, which is brought to the discharge side of the pump between the teeth and the casing. The liquid is pulled out the discharge port while the teeth return to mesh. Two equal gears are rotated against each other by external gear pumps. Both gears are mounted on a shaft with bearings on both sides.

01 Rotary external gear pump Hydraulics and pneumatics Hydraulics and pneumatics Rotary pump

Vane Pumps

The vanes, which are blades, buckets, rollers, or slippers, act with a cam to pull fluid into the pump chamber and drive it out. Vanes can be used in either the rotor or the stator. Pumping components for vane-in rotor pumps may be either fixed or variable displacement.

01 Rotary vacuum vane pump Hydraulics and pneumatics Hydraulics and pneumatics Rotary pump

Lobe pump

Between the rotor teeth and the pumping chamber, fluid is transported. Continuous sealing is created by the rotor surfaces. Timing gears drive all gears and synchronise them. Biwing, trilobe, and multilobe rotors are available configurations.

01 Rotary lobe pump Hydraulics and pneumatics Hydraulics and pneumatics Rotary pump

Screw pump

Fluid is carried in the gaps between the screw threads by screw pumps. When the screws mesh, the fluid is displaced axially. Progressive cavity pumps are a type of single screw pump. They have an externally threaded rotor and an internally threaded stator. The rotor threads are offset from the rotating axis.

01 Rotary screw pump Hydraulics and pneumatics Hydraulics and pneumatics Rotary pump

Piston pumps

Fluid travels from the inlet to the outlet through the gaps between the piston surfaces. Each rotor can have one or more piston parts, and each rotor must be timed separately.

01 Rotary cam and piston pump Hydraulics and pneumatics Hydraulics and pneumatics Rotary pump

Applications of Rotary pumps

Rotary pumps are ideal for pumping oil and other viscous liquids. Rotary pumps are used in the engine room to handle lube oil and fuel oil, and they can handle liquids with a wide variety of viscosities.

Advantages of Rotary Pumps

To minimise leakage (Slippage) from the discharge side back to the suction side, rotary pumps are equipped with very limited clearance between moving parts and stationary parts. To ensure these clearances, rotary pumps are configured to run at low speeds.

Disadvantage of Rotary Pumps

Higher speed activity induces corrosion and unnecessary wear, resulting in increased clearances and a reduction in pumping capability.