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External Gear Pumps: Functions and Definitions

Table of Contents
1. What are External Gear Pumps?
2. How Do External Gear Pumps Work?
3. Types of External Gear Pumps
4. Applications of External Gear Pumps
5. Advantages of External Gear Pumps
6. External Gear Pumps Maintenance and Care
7. Common Issues and Troubleshooting


What are External Gear Pumps?

External gear pumps are a type of positive displacement pump widely used in various industries for fluid transfer and handling applications. These pumps are known for their precision, efficiency, and versatility. The fundamental concept behind their operation lies in the meshing of two precisely machined gears - the driving gear (rotor) and the driven gear (idler) - that rotate externally. As the gears mesh together, they create a sealed cavity within the pump casing, trapping the fluid and propelling it from the inlet to the outlet.


Rexroth External Gear Pump and Internal Gear Pump


How Do External Gear Pumps Work?

External gear pumps are fascinating machines that employ a positive displacement principle to transfer fluids efficiently and precisely. These pumps consist of two interlocking gears, a driving gear (rotor), and a driven gear (idler), which mesh externally to create a sealed pumping chamber. Heash takes you to understand the principle of External Gear Pumps:

Gear Meshing and Cavity Formation: The process begins when the pump is primed, and the gears start rotating. As they rotate, the teeth of the driving gear and the driven gear mesh together externally, creating a series of voids or cavities between them. The size of these cavities changes as the gears rotate.

◘ Inlet Stage - Fluid Suction: As the cavities open up at the suction side of the pump (inlet), fluid is drawn into the pump through the inlet port due to the increasing volume of the cavities. This process is continuous, ensuring a steady flow of fluid into the pump.

◘ Fluid Trapping and Transport: As the gears continue to rotate, the cavities move along the outer perimeter of the gears, trapping the fluid inside. The trapped fluid is then carried by the gears from the inlet side to the discharge side of the pump.

◘ Outlet Stage - Fluid Discharge: At the discharge side of the pump (outlet), the cavities become smaller, compressing the fluid within them. This compression increases the pressure of the fluid, pushing it towards the outlet port.

◘ Fluid Discharge and Repeat: The compressed fluid is then forced out of the pump through the outlet port, and the cycle repeats with each revolution of the gears. The continuous meshing and unmeshing of the gears ensure a continuous flow of fluid through the pump.


Types of External Gear Pumps

External gear pumps, known for their efficiency and versatility, come in various configurations to suit different applications and industries. Let us understand the different types of external gear pumps:

◘ Standard External Gear Pumps:

Standard external gear pumps are the most common type, featuring two spur gears with external teeth that mesh together to create fluid flow. They are widely used in general fluid transfer applications, ranging from low-viscosity fluids to mildly viscous liquids. These pumps are well-suited for applications that require moderate pressure and flow rates.

◘ Magnetically Coupled External Gear Pumps:

In environments where the prevention of fluid leakage is crucial, magnetically coupled external gear pumps offer a reliable solution. These pumps feature a magnetic coupling between the driving gear and the driven gear, eliminating the need for traditional mechanical shaft seals. This design ensures a hermetically sealed pumping chamber, preventing leaks and enhancing safety in handling hazardous or corrosive fluids.

◘ Bi-Directional External Gear Pumps:

Bi-directional external gear pumps have the unique ability to operate in both directions. This feature allows them to reverse the flow of the pumped fluid, making them suitable for applications that require bidirectional fluid transfer. Industries such as hydraulics, where the direction of fluid flow might need to change, benefit from the versatility of bi-directional external gear pumps.

◘ Internal Bearing External Gear Pumps:

Internal bearing external gear pumps are equipped with bearings that are located inside the pump casing. These bearings provide support for the gears and reduce shaft deflection, resulting in improved pump efficiency and longevity. This type of gear pump is commonly used in applications where precise fluid handling is critical, such as metering and dosing processes.

◘ High-Pressure External Gear Pumps:

High-pressure external gear pumps are engineered to handle demanding applications that require pumping fluids at elevated pressures. These pumps are built with reinforced components and specialized seals to withstand the high forces involved in boosting fluid pressure. They find extensive use in hydraulic systems, pressure testing, and industrial machinery.


Applications of External Gear Pumps

External gear pumps find extensive applications across various industries, owing to their versatility, efficiency, and precision in fluid handling. Let Heash walk you through some key applications in three salient areas:

1) Automotive Industry:

The automotive sector heavily relies on external gear pumps for several critical functions, contributing to the smooth operation and performance of vehicles:

a) Engine Lubrication: External gear pumps deliver a steady flow of lubricating oil to engine components, reducing friction and wear. This ensures optimal engine performance and longevity.

b) Fuel Transfer: In fuel delivery systems, these pumps are utilized to transfer gasoline or diesel from the fuel tank to the engine, maintaining consistent fuel flow.

c) Power Steering: External gear pumps play a crucial role in power steering systems, assisting drivers in turning the wheels with ease and precision.

d) Hydraulic Systems: Automotive hydraulic systems, such as brake systems and transmission controls, utilize external gear pumps to provide the necessary hydraulic pressure for efficient operation.


2) Industrial Manufacturing:

In the industrial manufacturing sector, external gear pumps perform various tasks, contributing to smooth production processes and enhanced efficiency:

a) Hydraulic Systems: These pumps power hydraulic systems in industrial machinery, enabling precise control and movement of components.

b) Lubrication: External gear pumps are used to deliver lubricants to moving parts in industrial equipment, reducing friction and extending machine life.

c) Cooling Systems: In cooling systems, these pumps circulate coolants, dissipating heat from industrial equipment and processes.

d) Metering and Dosing: External gear pumps excel in accurate metering and dosing applications, ensuring precise delivery of chemicals and additives in manufacturing processes.


3) Oil and Gas Sector:

The oil and gas industry extensively relies on external gear pumps for various operations, contributing to the exploration, extraction, and transportation of petroleum products:

a) Oil Transfer: External gear pumps are employed in oil transfer and loading/offloading applications, facilitating the movement of crude oil and refined products between tanks and pipelines.

b) Lubrication and Cooling: These pumps play a vital role in providing lubrication and cooling for rotating equipment, such as compressors and turbines.

c) Metering and Dosing: In the oil and gas sector, precise metering and dosing of chemicals are crucial for effective processes, and external gear pumps ensure accurate delivery.

d) Hydraulic Systems: External gear pumps are used in hydraulic systems for controlling valves, actuators, and other essential equipment in drilling and extraction operations.


Advantages of External Gear Pumps

External gear pumps offer numerous advantages that make them a popular choice for fluid handling applications across various industries. Such as:

1) High Efficiency:

One of the significant advantages of external gear pumps is their high efficiency. These pumps are designed to minimize internal leakage, resulting in excellent volumetric efficiency. As the gears mesh externally, the fluid is trapped in the cavities and is continuously moved from the inlet to the outlet, ensuring a smooth and consistent flow. The efficient transfer of fluid reduces energy consumption, making external gear pumps an economical option for long-term operation.

2) Viscosity Range:

External gear pumps are well-suited for handling a wide range of fluid viscosities. They can effectively handle both low-viscosity liquids, such as fuels and solvents, as well as highly viscous substances, such as oils and adhesives. The pump's positive displacement principle ensures that the flow rate remains constant regardless of changes in fluid viscosity, making them versatile and adaptable to various applications.

3) Self-Priming Ability:

External gear pumps exhibit excellent self-priming capability, meaning they can automatically draw fluid into the pump without the need for manual priming. When the pump is started, the rotating gears create a vacuum at the inlet, causing the fluid to be drawn into the pumping chamber. This self-priming ability reduces the need for additional equipment or manual intervention, simplifying the operation and enhancing the pump's overall reliability.


External Gear Pumps Maintenance and Care

Regular Inspection and Cleaning:

Regular inspection is the cornerstone of effective maintenance for external gear pumps. By conducting routine checks, operators can identify potential issues early and prevent major problems. Here are some key steps for inspection and cleaning:

◘ Visual Inspection: Regularly inspect the pump's external components, including the casing, gears, and shaft. Look for signs of wear, corrosion, or damage. Pay attention to any leaks or unusual noises during operation.

◘ Inlet and Outlet Ports: Check the inlet and outlet ports for debris or clogging. Clean these ports to ensure unobstructed fluid flow and prevent damage to the pump.

◘ Seals and Gaskets: Examine the seals and gaskets for signs of wear or leakage. Replace any damaged seals promptly to maintain the pump's efficiency and prevent fluid leaks.

◘ Fluid Quality: Monitor the quality of the pumped fluid regularly. Contaminated or degraded fluids can damage the pump components, so it's essential to use the correct fluids and change them as recommended by the manufacturer.

◘ Cooling and Lubrication: Ensure that the pump is adequately cooled and lubricated. Check the lubricant levels and cooling systems regularly to prevent overheating and premature wear of gears and bearings.


Replacing Worn-out Parts:

Replacing worn-out or damaged parts is critical to maintaining the pump's efficiency and preventing costly breakdowns. Here are some key considerations for part replacement:

◘ Gears and Bearings: Gears and bearings are critical components that experience wear over time. Replace these parts when they show signs of wear or if there is increased play in the gear meshing. Properly lubricate new bearings during installation.

◘ Shaft Seals: Shaft seals are essential for preventing fluid leakage. If seals show signs of wear or failure, such as fluid leaks or excessive play, replace them promptly with suitable replacements.

◘ O-Rings and Gaskets: Check O-rings and gaskets for signs of wear, cracks, or deterioration. Replace these seals with compatible ones to maintain the pump's integrity and prevent leaks.

◘ Couplings and Mountings: Inspect couplings and pump mountings for any signs of misalignment or damage. Properly align and secure the pump to avoid undue stress on its components.

◘ Drive Mechanism: If the pump is belt-driven or operated by a motor, regularly inspect the drive mechanism and tension to ensure smooth operation.


Common Issues and Troubleshooting

1. Overheating:

Issue: Overheating is a common problem in external gear pumps and can occur due to various reasons, such as excessive friction, improper lubrication, or high fluid temperatures. Overheating can lead to pump damage, reduced efficiency, and fluid degradation.

Troubleshooting Steps:

• Check Lubrication: Insufficient or improper lubrication can cause excessive friction and overheating. Ensure that the pump's bearings and gears are adequately lubricated with the manufacturer-recommended lubricants.

• Verify Fluid Temperature: Verify the temperature of the pumped fluid. If the fluid temperature is too high, consider using a cooling system to maintain the fluid within the recommended operating range.

• Inspect Pump Speed: Running the pump at excessively high speeds can lead to increased friction and heat generation. Ensure that the pump is operated within its recommended speed limits.

• Inspect System Pressure: High system pressure can contribute to overheating. Ensure that the pump's pressure rating matches the system requirements and that the relief valve is functioning correctly to release excess pressure.

• Check for Obstructions: Blocked or restricted fluid passages can lead to increased pressure and overheating. Inspect the inlet and outlet ports for any obstructions and clear them if necessary.


2. Leakage Problems:

Issue: Leakage is a common problem that can occur in external gear pumps and can lead to fluid loss, reduced efficiency, and safety hazards.

Troubleshooting Steps:

• Inspect Seals and Gaskets: Check the seals and gaskets for signs of wear, damage, or misalignment. Replace any damaged or worn-out seals and ensure proper alignment during installation.

• Verify Shaft Seals: Shaft seals are critical for preventing fluid leakage. If there is leakage around the shaft, replace the shaft seals with suitable replacements.

• Examine Pump Casing: Inspect the pump casing for cracks, damage, or misalignment. Damaged casings can cause leakage and may need to be repaired or replaced.

• Verify O-Rings: O-rings are essential for sealing various connections and ports. Check the O-rings for signs of wear or deterioration and replace them as needed.

• Confirm Tightening of Connections: Ensure that all connections, bolts, and fittings are properly tightened to prevent any leakage from joints.

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