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

What is a Gear Pump?

A gear pump is a favorite type of pump from the category of positive displacement pumps. In a gear pump, a certain amount of liquid is sealed off by intermeshing gears, and the liquid is transmitted when the gears rotate to move it. Johannes Kepler invented the gear pump around 1600.

The hrdraulic gear pump transfers a pulseless flow that is directly proportional to the gear speed. These pumps are mainly used to generate high pressure. Generally, these use for pumping highly viscous liquids like adhesives, liquid fuels, motor oils, and 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 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.

The power gear connects with the prime mover or a mechanical power source. An internal combustion engine, electric motor, or manual labor uses to rotate a power or driver gear. This gear also knows as master gear, and idler gears also known as slave gears.

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 fully mesh 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 major components:

  1. Drive shaft
  2. Seal
  3. Inlet & Outlet ports
  4. Dirver gear
  5. Drive gear
  6. Housing 

gear pump components

1) Driver or Power Gear

The driver or power gear connects with a prime mover. This gear turns with the power of the prime mover.

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 the part of the pump from where the liquid sucks inside the pump. Low-pressure liquid enters into the pump from the inlet section.

5) Outlet Section

This is the part of the gear pump that delivers compressed liquid to the area of ​​interest. The high-pressure fluid exits the pump through the outlet.

6) Pressure relief valve or safety valve

This valve installs on the outlet section so that it can be released in the event of excess pressure to prevent the pump from any damage.

7) Prime mover

The gear pump uses a prime mover to drive the shaft on which the power gear is located. It can be driven by manual labor, 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, power gear drives by an electric motor or IC engine that further rotates the driven gear. Sometimes, both shafts can drive through a motor. These shafts are hold up with different bearings on both sides of the housing.

external gear pump

  1. When the gears on the pump suction side are come out of interlocking, the volume increases at the suction side. As these gears begin to spin against the pump housing, fluid moves into the cavity and traps by the teeth of the gears.
  2. This trapped liquid travels around the housing from inlet to outlet.
  3. When the gear teeth mesh on the pump outlet side, the volume reduces, and the liquid is forcibly drained under pressure.

As the gears mesh, 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.

Advantage 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 expansive 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 largest gear is the internal gear, such as its teeth protrude inward. Within this area, the smallest external gear is located eccentrically. It is designed to work with the rotor so that the gear teeth mesh occurs at specific points. A bushing and pinion are mounted in the pump housing to hold the idler in place.

internal gear pump

The internal gear pump has self-priming, non-pulsating, and 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 easy to use and maintain.

  1. 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.
  2. This trapped liquid travels around the housing from inlet to outlet.
  3. When the gear teeth mesh on the pump outlet section, the volume reduces, and the liquid forcibly drains under pressure.

Advantage 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

The lobe pump works like an external gear pump such as the liquid flows inside the housing. This hydraulic pump uses lobes instead of gear teeth. It can use three or four lobes according to the requirements.

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 locate 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. Due to the fewer lobes and larger lobes size, higher discharge can be achieved by this pump.

Lobe Pump

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 without a crescent shape. The rotor is the inner gear (power gear), and the driven is the outer gear.

These gear pumps are particularly appropriate for clean, low-pressure functions like hot oil filtration system and lubrication system but can also be found in hydraulic low to medium pressure applications.

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 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. Following are some factors that 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 Pump

The hydraulic gear pumps have the following advantages and disadvantages:

Advantages of Gear Pump

  1. These ensure a constant and even flow.
  2. Gear pumps have self-priming capabilities.
  3. It can pump highly viscous liquids.
  4. It is very insensitive to contamination.
  5. These types of pumps can work in both directions. Therefore, a single pump may be utilized for both loading and unloading.
  6. Gear pumps have a very compact and simple design.
  7. Also, use this pump for high viscous liquids such as oil that can’t pump with a centrifugal pump.
  8. This pump can generate very high pressures equal to 3000psi.
  9. It has low cost
  10. These type of hydraulic pumps have a very low maintenance cost.
  11. 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

  • These produce very high noise.
  • 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.

Applications of Gear Pumps

  • Food: Animal food, molasses, vegetable oils and fats, sugar, fillers, cacao butter, chocolate, etc.
  • Pulp and paper: Sludge, latex, lime, kaolin, black liquor, lye, soap, acid, etc.
  • Adhesives and resins.
  • Chemicals: Isocyanates, mixed chemicals, plastics, acids, sodium silicate, etc.
  • Petrochemicals: lube oils, crude oils, diesel oils, pitch, filled or pure bitumen, etc.
  • Ink and paint.

FAQ Section

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

When you decide the 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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