How does a Gear Pump work? | What Is a Gear Pump?

A gear pump is one of the most famous types of pumps from the category of positive displacement pumps. The gear pumps use a series of gears to pump the fluid. This article explains the gear pump working, types, and applications. 

What is a Gear Pump?

A gear pump is a type of pump that uses a series of rotating gears to pump the fluid. The gear pump usually has two gears. One gear knows as the idler gear or the driven gear and the second gear knows as the power or the driver gear.

These gears rotate in opposite directions and produce a suction force at the inlet side of the pump and a pressure force at the outlet side. 

The power gear is attached to the prime mover or a mechanical power source. An internal combustion engine, electric motor, or manual labor is used to rotate the driver gear. This gear is also known as master gear, and idler gear is also known as slave gear.

As the gears rotate, the fluid is trapped between the teeth of the gears and is transferred from the inlet to the outlet of the pump with the movement of the gears.

The hydraulic gear pump transfers a pulseless flow that is directly proportional to the gear speed. These pumps are mainly used to generate high pressure. These pumps have a simple, efficient, and compact design. 

The gear pumps are most commonly used for pumping highly viscous liquids like adhesives, liquid fuels, motor oils, hydrocarbons, etc.

Gear pumps have fixed displacement; therefore, these are known as positive displacement pumps.  

A positive displacement pump means that the pump delivers a uniform flow rate at a uniform speed irrespective of pressure changes. A fixed displacement represents that this pump delivers a constant amount of liquid with every shaft’s revolution.

Gear Pump Working

Gear pumps use the motion of the rotating gears to move liquids. A gear pump works on the basic principle of positive displacement. It works in the following way:

gear pump working

  • At the start-up stage, the gear pump starts working when the energy is supplied to the drive shaft then the driver or power gear begins to revolve by utilizing the power of the prime mover.
  • The driven or idler gear (that meshes with the power or driver gear) also revolves with the rotation of the power gear, but it rotates in the reverse direction. When these two gears start to rotate, a partial vacuum starts generating on the suction side of the pump.
  • When the vacuum is generated, then the suction-side fluid is sucked into the gear.
  • After this processing, the sucked fluid is blocked between the housing and the gear.
  • Then the blocked fluid between the gear teeth and the housing moves as the gear teeth rotate, and this fluid flows from the inlet side to the outlet side.
  • Similarly, in a driven gear, the fluid also flows from the inlet side to the outlet side, and the high-pressure fluid is also discharged from the outlet side of the pump.
  • Since the driver and driven gears of a gear pump are fully meshed with each other and there is no room for the fluid to move. Therefore, the fluid can’t flow directly toward the outlet side or from the inlet side to the outlet side. For the fluid flow inside the pump, the movement of these gears is very compulsory, and without their movement, fluid can’t flow.

Components of Gear Pump

The gear pump has the following components:

  1. Drive shaft
  2. Seal
  3. Inlet & Outlet ports
  4. Driver gear
  5. Drive gear
  6. Housing 
  7. Prime mover
  8. Pressure relief valve

gear pump components

1) Driver or Power Gear

The driver or power gear is attached to a prime mover. It gets power from the prime motor. When the mover shaft rotates, the driver gear also rotates.

2) Idler or Driven Gear

The idler gear meshes with the power gear. It revolves with the rotation of the power gear.

3) Housing

Both the power gear and the idler gear are located inside the hydraulic gear pump housing.

4) Inlet Section

This is a part of the pump from where the liquid is entered into the pump. Low-pressure liquid enters the pump from the inlet section.

5) Outlet Section

This is a part of the gear pump from where the compressed fluid is discharged. When the fluid is compressed, its pressure becomes and it discharges through the outlet port.

6) Pressure Relief Valve

This valve is located in the outlet section. When the fluid pressure inside the pump becomes more than a specified limit, the pressure relief valve automatically opens and discharges the extra pressure into the environment. It prevents the pump from any damage.

7) Prime Mover

The gear pump uses a prime mover to run the shaft on which the power gear is located. It can be driven by manual labor, an IC engine, or an electric motor.

Types of Gear Pumps

Gear pump has the following major types:

  1. External Gear Pump
  2. Ge- Rotor Pump
  3. Internal gear pump
  4. Lobe Pump

1) External Gear Pump

The external gear pump has two identical gears (power and driven gears) that rotate in opposite directions. Usually, the power gear is run by an electric motor or IC engine that further rotates the driven gear. The power gear is connected to the electric motor through a shaft.

Sometimes, both shafts can be driven through a motor. These shafts are held up with different bearings on both sides of the housing.

external gear pump

  • When the gears on the suction side of the pump come out of interlocking, the volume increases at the suction side and a vacuum creates. As the gears begin to spin against the pump housing, fluid enters the pump cavity and traps in between the teeth of the gears.
  • This trapped liquid flows along with the movement of the driver and driven gears around the housing from the inlet side to the outlet side.
  • When the teeth of these gears meshed on the pump outlet side, the fluid volume reduces, and the liquid is forcibly discharged at high pressure.
  • When the gears are meshed, the liquid can’t return from the center between the gears.

Due to the tight tolerance between the housing and the pump gears, the pump creates suction at the suction side and prevents liquid from going back from the outlet section (although low-viscosity liquid leakage is more likely to occur). With an external gear pump, herringbone gears, helical gears, or spur gears can use.

Advantages and Disadvantages of External Gear Pumps

This pump has relatively quiet workingNo solids are acceptable
High speedThese pumps have fixed-end clearance
No extended bearing loadFour bushings in the fluid region
Design assists extensive variation of materials 
High speed 
It has easy maintenance. 
Less expensive to design than an internal gear pump. 
Good reliability 

Read More: Different Types of Pumps

2) Internal Gear Pump

The principle of operation of the internal gear pump is the same as the external gear pump. But the internal pump has dissimilar sizes of the two meshing gears, and one meshing gear rotates in the other.

The internal gear pumps use an internal rotor with external teeth (the idler) and an external rotor with internal teeth (the gear) to pump liquids.

The gears of the pump turn in opposite directions. The teeth of these gears mesh with each other to produce a tight seal between the inlet and outlet ports of the pump.
An external source, such as an engine or an electric motor, is used to drive the external gear, while the external gear runs the idler gear through the meshing of their teeth. When these gears start rotating, a specific amount of liquid is trapped between the gears’ teeth and is transferred from the inlet section to the outlet section of the pump.

A bushing and pinion are mounted in the pump housing to hold the idler in place.

internal gear pump

The internal gear pump has a self-priming ability. They supply non-pulsating fluids. They may work dry for a short time. This pump is also bi-rotational, which means you can use the same pump to load and unload containers. These pumps have high reliability and are easy to use and maintain.

Internal gear pumps are commonly used for high-viscosity fluids, such as adhesives, paints, and oils.

An internal gear pump works in the following way:

  • When the gears on the suction side of the pump are disengaged, the volume increases. As the gears continue to turn relative to the pump housing and diaphragm, the liquid moves into the cavity and imprisons by the teeth of the gears.
  • This trapped liquid travels around the housing from the inlet to the outlet.
  • When the gear teeth mesh on the pump outlet section, the volume reduces, and the liquid forcibly drains under pressure.

Advantages and Disadvantages of Internal Gear Pumps

Its maintenance is easyIt has a high price
Low NPSH neededCantilever load on the bearing
Operates at moderate pressureMedium pressure limit
It has only two moving componentsUsually needs average speed
Best suitable for high viscous fluids 
Non-pulsating release 
Only a single stuffing box 
Its flexible design allows you to
customize your application.
One-sided adjustable clearance 
Normal operation in any direction 
Even and constant fluid release irrespective
of the pressure conditions.

Read Also: Types of Positive displacement Pumps

3) Lobe Pump

A lobe pump uses two or more rotating lobes to pump fluids. The lobes have a similar design like gears, but with a rounded profile. These lobes rotate in opposite directions. 

The lobe pump works like an external gear pump such as the liquid flowing inside the housing. It can use three or four lobes according to the requirements. As the lobes rotate, the fluid is trapped between them and transports from the inlet to the outlet of the pump.  

In contrast to the external gear pump’s gears, the lobes don’t touch each other. The external steering wheel of the gearbox prevents the lobes from touching.

The support bearings of the pump shaft are located inside the gearbox. Since these bearings are not in the pumped fluid, the pressure is restricted by the deflection of the shaft and the position of the bearing, which lessens the noise level of the pump.

Lobe Pump

Lobe pumps are usually used for high-viscosity fluids, such as creams, pastes, and slurries. They can handle solids up to a specific size. These pumps also have the ability to handle shear-sensitive fluids without damaging the fluid structure.

Advantages of Lobe Pump

  • Changes in rotation cause a flow reversal.
  • Easy maintenance
  • High flow density
  • Great free-throw channel
  • Low pulsation
  • Continuous flow
  • Precise dosage
  • The flow is proportional to the speed

4) Ge-Rotor Pump

The Ge-rotor pump is an internal gear pump that uses two intermeshing rotors to transfer fluids. The rotors of the pump have a helical shape. These rotors have a complex design that permits them to produce a tight seal between the inlet and outlet ports of the pump.

When the rotors rotate, they trap the liquid in the area between the rotors and the pump casing and transfer it from the inlet port to the outlet port.

These pumps are usually used for low to high-viscosity liquids, as well as fluids containing gases or solids. The G-rotor pumps are usually used in beverage production, chemical processing, and the food and oil and gas industry.

These pumps have high efficiency and high flow rates. They also have the capability to control a wide range of fluid temperatures and viscosities.

The working of the Ge-rotor pump is given below:

Ge-rotor pump

  1. Fluid introduces in the inlet side between the driven gear and rotor.
  2. The fluid flows through the pump between the teeth of the “gear within a gear” principle. The tight tolerances among the gears act as a closure between the inlet and outlet openings.
  3. The teeth of the rotor and idler gear; fully engage in producing an equidistant seal between the outlet and inlet. This seal forces the fluid to drain through the outlet port.

Advantages and Disadvantages of Ge-rotor pump

Quiet workingFixed clearance
Only a single stuffing boxModerate pressure limit
Works well in both directionsCantilever load on the bearings
High speedSolids are not allowable
It has two rotating components 

Read More: Different types of Hydraulic Pumps

Screw Pump vs Gear Pump

Screw PumpGear Pump
A screw pump uses screws to pump the fluids.A gear pump uses gears to pump the fluids.
It generates low operation vibration.It generates high operational vibration.
The screw pump has low operational noise.The gear pump has high operational noise.
The screws have a small diameter than the diameter of gears.The gears have a large diameter.
These pumps have excellent suction.These don’t have good suction as screw pumps.
They have long service life than gear pumps. The gear pump has short service life than the screw pump.
They consume less power.They consume high power, which increases the energy cost.
It has a smaller footprint due to that it can easily install in a small area. It has a large footprint due to that it requires a large area for installation.

Read Also: Working of Screw Pump

Difference between the Gear Pump and Peristaltic Pump

The major difference between the peristaltic pump and the gear pump is given below:

Peristaltic PumpGear Pump
The volume of the pump varies due to the flexible tube.It has a fixed volume.
The peristaltic pump provides more pulsating flow.It provides less pulsating fluid.
It has the capability to handle high-viscosity fluids.It can’t handle high-viscosity fluids.

See More: Working of Peristaltic Pump

Efficiency of Gear Pump

The efficiency of the hydraulic gear pump is very low, particularly in the case of high-pressure applications. The following factors affect the efficiency of the gear pumps:

  • Clearances: The linear clearance between the end of the gear and the outside diameter permits the backflow and leak. Though, increasing the clearance can decrease hydrodynamic friction and improve efficiency.
  • Gear Clearance: Large gear clearance can also lead to liquid leaks. But this also helps to decrease the waste of energy by trapping liquid between the gear teeth.

Advantages and disadvantages of Gear Pumps

The hydraulic gear pumps have the following advantages and disadvantages:

Advantages of Gear Pumps

  • These ensure a constant and even flow.
  • Gear pumps have self-priming capabilities.
  • It can pump highly viscous liquids.
  • It is very insensitive to contamination.
  • These types of pumps can work in both directions. Therefore, a single pump may be utilized for both loading and unloading.
  • Gear pumps have a very compact and simple design.
  • This pump may also be used for highly viscous liquids such as oil that can’t be pumped with a centrifugal pump.
  • Gear pumps produce very little noise compared to other types of pumps.
  • It has a low cost
  • These types of hydraulic pumps have a very low maintenance cost.
  • When pumping a very high viscous fluid (such as engine oil) with a gear pump, the chance of a leak is minimal. Therefore, when pumping a very high viscous liquid, the efficiency of the pump improves.

Disadvantages of Gear Pumps

  • Gear pumps have a limited viscosity range. They are not best suitable to pump very high-viscosity or very low-viscosity fluids.
  • A gear pump uses meshing gears; therefore, abrasive fluid can’t use in it.
  • Due to the limited size of the gear pump, it can’t use for high-capacity flow rates.
  • They are not ideal for extreme temperature ranges.
  • They are not ideal for high-pressure applications.
  • Gear pumps are prone to cavitation.
  • These pumps need precise alignment between the gears to work efficiently.

Applications of Gear Pumps

  • Food: The gear pumps are used for animal food, molasses, vegetable oils and fats, sugar, fillers, cacao butter, chocolate, etc.
  • Pulp and paper: They are used in pulp and paper industries to pump sludge, latex, lime, kaolin, black liquor, lye, soap, acid, etc.
  • Marine: Gear pumps are used in marine applications to pump fuel, lubricants, and hydraulic fluids in ships and boats.
  • Chemicals: They are used to pump different chemicals such as isocyanates, mixed chemicals, plastics, acids, sodium silicate, etc.
  • Petrochemicals: They are used to pump lube oils, crude oils, diesel oils, pitch, filled or pure bitumen, etc.
  • Automotive: Gear pumps are used in automotive applications to pump fluids such as coolant, power steering fluid, transmission fluid,  and engine oil.
  • Pharmaceutical: Gear pumps are used in the pharmaceutical industry to pump different fluids, including chemicals, medicines, and vaccines.

FAQ Section

What is the material that should be considered for the gear pump construction?

When you decide material for the construction of a gear pump, the factors that must be considered are; initial material costs, replacement costs, and shelf life. In addition to considering the liquid itself when choosing a structural material, there are also concentrations, contamination, and temperature of the fluid to consider.

Standard materials for pump components such as bronze, cast iron, and mild steel tend to be cheaper initially. However, if these materials lead to premature failure, unexpected repairs, and replacements, the price will be higher. Some low-speed gear pumps may require upgrading the rotor material from cast iron to steel as the viscosity increases to withstand increased torque due to viscosity.

Is priming required in the gear pump?

The gear pump is a self-priming pump. It means that this pump doesn’t need priming. This is one of the main benefits of this pump. In addition, it has high volumetric efficiency and can be stably transported at a constant speed.

Who invented gear pump?

Johannes Kepler invented the gear pump around 1600.

What causes the suction of fluid into the gear pump?

A gear pump uses a series of rotating gears to transfer fluid from one place to another. The rotating gears create a fluid seal between the housing of the pump and generate suction at the inlet side. As the pressure on the inlet side becomes lower than the surrounding pressure, the suction process of the fluid starts.

See More
  1. What are different types of Pumps?
  2. How does an Electric Vacuum Pump Work?
  3. Different types of Hydraulic Pumps
  4. How does a Centrifugal Pump work?

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