Gear Pump

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A gear pump uses the meshing of gears to pump fluid by displacement.  Due to their simplicity, versatility and their high reliability they are one of the most common types of pumps for hydraulic fluid power applications.  Gear pumps, however, are also widely used in chemical installations to pump fluid with a wide range of viscosities.  Internal gear pumps can pump fluids with viscosity ranges from 1cPs to over 1,000,000cP.  The gear pump also has the ability to pump fluids at very high temperatures, in excess of 700o.

Gear Pump Index

There are two main variations; external gear pumps which use two external spur gears, and internal gear pumps which use an external and an internal spur gear.  Gear pumps are fixed displacement, meaning they pump a constant amount of fluid for each revolution.  Some gear pumps are designed to function as either a motor or pump.

The most common design of an external gear pump is where one of the gears is driven by a motor and the other runs free.  A partial vacuum, created by the unmeshing of the rotating gears, draws fluid into the pump.  This fluid is then transferred to the other side of the pump between the rotating gear teeth and the fixed casing.  As the rotating gears mesh together, they generate an increase in pressure.  Depending on the number of teeth, the "idler" gear might be driven directly by the "drive" gear.  In other cases an extra gear external to the pump drives the secondary gear at the same rate.

External gear pumps can come in single or double (two sets of gears) pump configurations with different types of gear designs.  These can be spur gears, helical gears, and herringbone gears.  The outlet flow of gear pumps is very smooth when compared to a piston pump.  However, among gear pumps, pumps with a delical or herringbone gears will have a smoother flow than spur gears. Large capacity external gear pumps typically use helical or herringbone gears.

Small external gear pumps usually operate at 1750 or 3450 rpm and larger models operate at speeds up to 640 rpm.  Gear pumps can run at pressures beyond 3,000 PSI making them well suited for use in hydraulics applications.

This pump will pump in the reverse direction if you reverse the direction of rotation of the gears.  Two pairs of valves can be added to make this a Reversing Gear Pump, which pumps in the same direction regardless of which direction the gears rotate.

Gear pump Types  

  • External Gear Pump  -
    • Spur Gear Pump  -  This is the most common type of external gear pump.  It consists of two spur gears that mesh together, with one gear being the driving gear and the other being the driven gear.  Fluid is trapped in the spaces between the gear teeth and is carried from the inlet to the outlet as the gears rotate.
    • Helical Gear Pump  -  Similar to spur gear pumps, but the gears have a helical shape.  This design reduces noise and provides smoother operation compared to spur gear pumps.
    • Herringbone Gear Pump  -  It has gears with a herringbone shape, which further improves the smoothness of the pumping action and reduces axial thrust.
    • Double Helical Gear Pump  -  Also known as a "double herringbone" pump, it combines the features of helical and herringbone gears to eliminate axial thrust and improve efficiency.
  • Internal Gear Pump  -
    • Rotary Gear Pump  -  Internal gear pumps have an outer rotor with external teeth and an internal rotor with internal teeth.  The gears rotate, and fluid is carried between the teeth and the housing from the inlet to the outlet.  These pumps are known for their quiet operation and ability to handle high viscosity fluids.
    • Crescent Internal Gear Pump  -  This variation of the internal gear pump includes a crescent shaped element that maintains the seal between the rotating and stationary gears.  It enhances the pump's efficiency and prevents fluid from leaking back.

Gear pumps are widely used in various industries for applications such as hydraulic systems, lubrication systems, chemical processing, and more.  The choice between external and internal gear pumps depends on factors like the viscosity of the fluid, pressure requirements, and the desired efficiency of the pump.


Gear Pump Advantages and Disadvantages

  • Gear pumps are positive displacement pumps, ensuring a consistent and precise flow of fluid, regardless of variations in pressure or viscosity.
  • Gear pumps are often compact and lightweight, making them suitable for installations where space is limited.
  • Gear pumps have a relatively simple design with fewer moving parts, resulting in easy maintenance and lower repair costs.
  • Gear pumps can achieve high volumetric efficiency, particularly with high viscosity fluids, providing a steady and reliable flow.
  • Many gear pumps are self priming, capable of evacuating air from the suction line, which can be advantageous in certain applications.
  • Gear pumps are often cost effective, providing good performance at a reasonable price, making them attractive for various industrial applications.
  • Properly designed and maintained gear pumps can operate at relatively low noise levels compared to some other types of pumps.
  • Many gear pumps can operate in both directions, allowing for reversible flow, which is useful in applications where fluid direction needs to be changed.
  • Gear pumps may have limitations on the maximum pressure they can handle.  In high pressure applications, other pump types, such as piston pumps, may be more suitable.
  • The efficiency and performance of gear pumps can be affected by temperature variations.  Care should be taken to ensure that the pump is suitable for the operating temperature range.
  • Gear pumps may have limitations on suction lift, especially in self-priming applications.  This can affect their ability to lift fluid from a lower reservoir.
  • In some cases, gear pumps can generate vibration and noise, particularly if not properly installed or if there is excessive wear.  This can be a consideration in certain applications.
  • Some gear pumps may not be suitable for pumping certain abrasive or corrosive fluids, as this can lead to wear and reduced pump life.
  • The tight clearances between gear teeth are critical for performance, and wear over time can lead to internal leakage, affecting efficiency.
  • Gear pumps may not be as efficient in handling low-viscosity liquids, and they may not be the best choice for applications where a constant flow of such fluids is required.


gear pump Characteristics

Gear pumps have several characteristics that make them suitable for specific applications.

  • Positive Displacement  -  Gear pumps are positive displacement pumps, meaning they move a fixed amount of fluid with each revolution.  This makes them suitable for applications where a precise and constant flow is required.
  • Compact Design  -  Gear pumps typically have a compact design, making them easy to install in various systems where space is limited.
  • Simple Construction  -  Gear pumps have a relatively simple construction with few moving parts.  This simplicity makes them easy to maintain and repair.
  • High Efficiency  -  Gear pumps can achieve high volumetric efficiency, especially in applications with high viscosity fluids.  They provide a consistent flow rate even under varying pressure conditions.
  • Suitable for Viscous Liquids  -  Gear pumps are well suited for handling viscous liquids, making them commonly used in applications involving oils, lubricants, and other high viscosity fluids.
  • Self-Priming  -  Some gear pumps are self-priming, meaning they can evacuate air from the suction line and create a suction lift.  This feature is advantageous in situations where the pump may be located above the fluid source.
  • Relatively Low Noise Levels  -  Gear pumps generally operate at lower noise levels compared to some other types of pumps, especially when properly designed and maintained.
  • Bi-Directional Operation  -  Many gear pumps can operate in both directions, allowing for reversible flow.  This characteristic is beneficial in applications where fluid direction needs to be changed.
  • Cost-Effective  -  Gear pumps are often cost effective and provide good value for their performance, especially in applications where their characteristics align with the requirements.
  • Limited Pressure Capability  -  Gear pumps may have limitations on the maximum pressure they can handle.  In high pressure applications, other types of pumps, such as piston pumps, may be more suitable.
  • Temperature Sensitivity  -  The efficiency and performance of gear pumps can be affected by temperature variations.  Care should be taken to ensure that the pump is suitable for the operating temperature range.

When selecting a gear pump for a specific application, it's essential to consider factors such as flow rate, pressure requirements, viscosity of the fluid, and the operating environment to ensure optimal performance.

gear pump Applications

Gear pumps find application in various industries due to their positive displacement nature, efficiency, and ability to handle different types of fluids.

  • Hydraulic Systems  -  Gear pumps are frequently used in hydraulic systems to provide the necessary fluid power for equipment such as lifts, cranes, and industrial machinery.
  • Lubrication Systems  -  Gear pumps are employed for circulating and delivering lubricating oil in engines, gearboxes, and other machinery to reduce friction and wear.
  • Chemical Processing  -  Gear pumps are suitable for transferring various chemicals and fluids in chemical processing plants.  Their ability to handle different viscosities makes them versatile in this application.
  • Oil and Gas Industry  -  Gear pumps are used in the oil and gas industry for applications such as transferring crude oil, diesel, and other petroleum products.
  • Automotive Industry  -  Gear pumps are used in automotive applications for tasks such as engine lubrication, transmission fluid circulation, and power steering.
  • Food and Beverage Industry  -  In the food and beverage industry, gear pumps are employed for transferring liquids such as syrups, chocolate, and other viscous substances.
  • Agriculture  -  Gear pumps are used in agricultural machinery for tasks like spraying fertilizers, transferring fluids, and powering hydraulic systems.
  • Plastics Industry  -  Gear pumps play a role in extrusion processes in the plastics industry, where they assist in maintaining a consistent flow of melted plastic through the production line.
  • Water Treatment  -  Gear pumps are used in water treatment plants for chemical dosing, where precise control of chemical flow is essential for the treatment process.
  • Printing Industry  -  Gear pumps are used in printing machines for ink circulation and distribution.  Their positive displacement characteristics contribute to consistent ink delivery.
  • Pulp and Paper Industry  -  Gear pumps are employed in the pulp and paper industry for tasks such as transferring various fluids in the papermaking process.
  • Textile Industry  -  Gear pumps are used in the textile industry for tasks such as dyeing and chemical processing where accurate fluid transfer is crucial.
  • Cooling Systems  -  Gear pumps are used in cooling systems, such as those found in industrial machinery and power plants, to circulate coolant and dissipate heat.
  • Marine Industry  -  Gear pumps are used in marine applications for tasks like fuel transfer, lubrication, and hydraulic systems on ships and boats.
  • Construction Equipment  -  Gear pumps are used in construction machinery for tasks like powering hydraulic systems in excavators, loaders, and other equipment.

The versatility, reliability, and efficiency of gear pumps make them a popular choice in a wide range of industrial applications across different sectors.

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