A gear pump is a positive displacement pump that moves fluid by trapping a fixed amount between interlocking gears and then pushing it through the pump. It provides a smooth, consistent flow that matches the speed of the gears. Explore Gear Pumps Explained: A Complete Overview and Guide With Shriank.
What are Gear Pumps?
Gear pumps are positive displacement pumps that use mechanical action to move fluids by trapping a fixed amount between gears and transferring it. Unlike centrifugal pumps, which rely on velocity to create pressure, gear pumps physically compress the fluid.
There are two main gear pumps: external gear pumps, which use two identical gears that mesh together, and internal gear pumps, where one gear is placed inside another. Invented in the 17th century by Johannes Kepler, gear pumps are commonly used in hydraulic systems and for handling thick fluids. They are self-priming and ideal for applications requiring lower flow rates and higher pressures.
Fluids discharged from a gear pump typically flow with low-pressure pulsations, resulting in a smooth and consistent flow. The flow rate is directly linked to the speed of the gears, making gear pumps ideal for applications where precise flow measurement is needed.
Electric motors usually power gear pumps, but they can also be driven hydraulically or mechanically, depending on the application. For example, many tractors use gear pumps for their hydraulic systems, with the pump mechanically connected to the engine.
The tight clearances and rotation speed of gear pumps help minimise fluid leakage, improving efficiency. Depending on the pump design, the material being pumped, known as “pumpage,” can include liquids, gases, or even solids.
What is an External Gear Pump? (Helical/Modular)
An external gear pump, often used for transferring viscous fluids at low speeds, ensures a smooth fluid discharge. This type of pump operates quietly due to its low speed and the design of its helical teeth. The helical gears are angled within the pump head, with a second set of gears behind the main teeth. This second set of gears serves to keep the unit balanced during operation. The gears are positioned one above the other, with one driven by a motor. As they rotate, fluid flows into the cavities between the teeth and casing, then moves towards the outlet.
What is an Internal (Eccentric) Gear Pump?
Internal gear pumps work similarly to external ones by filling the spaces between the teeth with liquid. The fluid enters the meshed cogs, and the idler moves it towards the outlet. These pumps require clean liquids because any impurities could interfere with the movement of the fluid due to the small gaps between the teeth.
These pumps use different seal types, such as single or double mechanical seals, gland packing, or magnetic coupling. Heating jackets can also be added to both pump styles to prevent liquids from solidifying inside the pump head.
Basic Parts of a Gear Pump
Let’s understand some of the important parts of a gear pump.
Housing: The outer casing that holds all the components together and keeps the gears aligned.
Gears: Two or more interlocking gears inside the housing, usually made of steel or bronze, that rotate to move the fluid.
Inlet and Outlet Ports: These are the openings in the housing that serve as the control points for the fluid flow. The inlet connects to the fluid source, and the outlet leads to the destination.
Drive Shaft: This component transfers power from an external source, such as an electric motor, to the gears, enabling them to rotate and move the fluid.
Bearings: These support the rotating gears, reducing friction and wear.
Seals and Gaskets prevent fluid leaks and ensure a tight seal between moving and stationary parts.
How Does a Gear Pump Work?
Inlet Phase: As the gears start to turn, fluid is drawn into the pump through the inlet. The space between the gear teeth and the pump housing expands, creating a low-pressure area that pulls the fluid in.
Transport Phase: The rotating gears trap the fluid in the spaces between the teeth and carry it from the inlet side to the outlet side.
Outlet Phase: When the fluid reaches the outlet, the gears mesh together, reducing the space and forcing the fluid out of the pump.
Continuous Cycle: This efficient process, which repeats with each turn of the gears, creates a steady flow of fluid. The amount of fluid moved, a testament to the gear pump’s efficiency, depends on the size and shape of the gears.
Main Uses for Gear Pumps
External gear pumps are often used to move water, light oils, and chemicals. They are ideal for precise dosing applications, like fuels, polymers, and chemical additives. Gear pumps work well even when pressure changes, making them useful in situations with an irregular supply.
Common Applications:
Water
Fuel and lube oils (used in engines and gearboxes)
Chemical dosing and polymer mixing
Industrial, agricultural, and hydraulic systems (like tractors and lifts)
Acid and caustic handling (using stainless steel or composite materials)
Resins and polymers
Alcohols and solvents
Limitations of Gear Pump Designs
Wear and Tear: Gear pumps can wear out when handling abrasive materials or sediments, decreasing efficiency and output as the cogs wear down.
Parts in Contact with Liquid: Bearings are immersed in the pumped liquid, making these pumps unsuitable for abrasive fluids. Regular checks for wear and vibration in bearings and bushings are necessary.
Hygiene Concerns: The design of gears and the immersion of parts in the liquid can make it difficult to maintain high hygiene levels. Other pump designs, like lobe or flexible impeller pumps, may offer better hygiene.
Handling Solids: Gear pumps can be oversized to handle solids, but this reduces efficiency.
Operating Characteristics
To optimise gear pump performance, minimising friction between parts is crucial. Friction generates heat, which can cause the pump components to expand. Since gear pumps, especially external ones, have tight clearances, any thermal expansion can damage the pump. This could result in misaligned gears, leading to wear, leaks, and reduced efficiency. In severe cases, the pump may seize and stop working altogether.
The pumped fluid usually lubricates the pump’s internal parts, so gear pumps aren’t suitable for extended dry operation. They perform best at their maximum design speed; operating at lower speeds reduces their efficiency.
Summary
A gear pump transfers fluid by trapping a set volume between interlocking gears, providing smooth, consistent flow based on the gear rotation speed. There are two main types: external, with two identical gears, and internal, with two different-sized gears.
Gear pumps are ideal for pumping high-viscosity fluids like oil or foodstuffs. They are also used where precise dosing or high pressure is needed. External pumps handle higher pressures, while internal pumps excel at suctioning and handling thicker fluids.
For reliable gear pumps, Shriank offers quality options suited for various applications.
