Gear Pump

Gear pumps are widely used positive displacement pumps in hydraulics that generate a flow of fluid through the rotation of intermeshing gears. They are essential for supplying power to hydraulic systems in a wide range of industrial and mobile applications. Their robust construction and ability to operate under high pressures make them a preferred choice for engineers and technicians who require reliable and efficient solutions for fluid delivery.

How a Gear Pump Works

The basic function of a gear pump is based on the principle of displacement. Two or more gears mesh inside a housing. One of the gears, known as the drive gear, is driven by an external motor. This drive gear, in turn, drives the driven gear(s).

Suction Process

On the suction side of the pump, the teeth of the gears move out of mesh. This increases the volume between the teeth and the housing, creating a vacuum. This vacuum draws the hydraulic fluid from the reservoir into the resulting gear chambers.

Discharge process

The enclosed fluid is transported by the rotating teeth along the housing wall to the discharge side. As the gears re-mesh on the discharge side, the volume between the teeth is reduced. The fluid is thereby displaced from the tooth chambers and delivered under pressure into the hydraulic system. A sealing wedge or a crescent-shaped element in internal gear pumps prevents a hydraulic short circuit between the suction and pressure sides.

Design and Components

Gear pumps consist of several key components that work together to ensure the pumping function.

Housing

The housing encloses the gears and forms the suction and discharge chambers. It is robustly constructed to withstand the pressures generated during operation.

Gears

The gears are the heart of the pump. External gear pumps use two identical gears, while internal gear pumps use an internally toothed ring gear and a smaller, externally toothed pinion.

Bearing Housings and Bearings

The gears are mounted in bearings that enable precise rotation and absorb radial and axial forces.

Drive shaft

The drive shaft transmits mechanical energy from the motor to the drive gear.

Types of gear pumps

There are various designs of gear pumps, which differ in their construction and specific characteristics. The most common types are external gear pumps and internal gear pumps.

External gear pumps

External gear pumps are the most commonly used gear pumps. They consist of two externally toothed gears that mesh with each other. One gear is driven and drives the other. The fluid is transported through the gaps between the teeth along the housing wall from the suction side to the discharge side.

Features of external gear pumps

• Simple design: Robust and cost-effective construction.
• High pressures: Can achieve pressures up to 280 bar.
• Compact design: Minimal space requirements.
• Wide range of applications: Versatile use in mobile and stationary hydraulic systems.

Internal gear pumps

Internal gear pumps consist of an externally toothed pinion that meshes with an internally toothed ring gear. Between the two gears is a crescent-shaped sealing wedge that separates the suction and pressure sides.

Features of internal gear pumps

• Low noise level: Particularly quiet operation, ideal for noise-sensitive applications.
• Good suction performance: Fills slowly with hydraulic fluid, resulting in smooth operation.
• High efficiency: Due to the continuous increase and decrease in volume.
• Compact design: Often space-saving despite a more complex construction.

Advantages and disadvantages of gear pumps

Gear pumps offer a number of advantages that make them attractive for many hydraulic applications, but they also have certain limitations.

Advantages

• Robust design: Insensitive to contaminants in the hydraulic fluid.
• High operational reliability: Reliable operation even under demanding conditions.
• Compact design: Small footprint, which facilitates integration into machines.
• Low cost: Often more economical to purchase compared to other pump types.
• Easy maintenance: Relatively simple design facilitates maintenance work.
• Constant flow rate: Delivers a steady flow, which is important for many applications.

Disadvantages

• Pulsation: The flow rate may exhibit slight pulsations, particularly in external gear pumps.
• Noise: External gear pumps may be louder than other pump types under certain conditions. Internal gear pumps, however, are significantly quieter.
• Limited pressure ranges: Although they can reach high pressures, they are often outperformed by axial piston pumps in extreme high-pressure applications.
• Efficiency: Volumetric efficiency may decrease at low speeds and high pressures.

Applications of gear pumps in hydraulics

Due to their versatility and robustness, gear pumps are used in numerous areas of hydraulics.

Mobile machinery

Gear pumps are indispensable in construction machinery such as excavators, wheel loaders, and cranes. They supply the hydraulic cylinders and motors responsible for moving the working equipment. They are also used in agricultural machinery such as tractors and harvesters.

Industrial equipment

In the manufacturing industry, gear pumps are used in machine tools, presses, injection molding machines, and other production equipment. They control movements, generate clamping forces, and enable precise positioning.

Material Handling

In material handling, for example in forklifts, lifting platforms, and elevators, gear pumps provide the necessary lifting force and movement.

Automotive

Gear pumps are also used in commercial vehicles such as trucks and municipal vehicles for power steering, tipping mechanisms, and other hydraulic functions.

Standards and Guidelines for Gear Pumps

The safety and performance of gear pumps in hydraulic systems are ensured by a series of standards and guidelines. These standards are critical for design, operation, and maintenance.

DIN EN ISO 4413

This standard is central to hydraulic drive systems and establishes general rules for design and safe operation. It addresses aspects such as pressure limitation, hose lines, and the documentation of hydraulic systems.

DIN EN ISO 12100

This standard addresses machine safety and provides general design principles that are also relevant for hydraulic control systems.

DIN EN ISO 13849 (Parts 1 and 2)

This series of standards addresses safety-related parts of control systems and supplements the requirements for hydraulic systems to ensure functional safety.

Mounting Standards (SAE, DIN, UNI)

International mounting standards such as SAE, DIN, and UNI are of great importance for the compatibility and interchangeability of gear pumps. These standards define the dimensions of flanges, shaft journals, and connections.

Hydraulic fluids

Selecting the right hydraulic fluid is critical for the service life and performance of a gear pump. Standards such as DIN 51 524 (Parts 2–3) and ISO VG 10–68 according to DIN ISO 3448 specify the requirements for hydraulic oils, including viscosity ranges and temperature resistance.

Maintenance and Servicing

Regular maintenance is crucial for the longevity and reliable operation of gear pumps.

Fluid Management

The cleanliness of the hydraulic fluid is of the utmost importance. Contaminants can lead to wear and failures. Regular filter changes and fluid analyses are therefore essential.

Leak Testing

Regular checks for leaks at seals and connections help prevent pressure losses and maintain the pump’s efficiency.

Wear Inspection

Monitoring noise levels, vibrations, and flow rate can provide early indications of wear. If necessary, worn components such as bearings or gears should be replaced.

Temperature monitoring

Overheating of the hydraulic fluid can significantly shorten the service life of the pump and other components. Monitoring the operating temperature is therefore important.

Conclusion

Gear pumps are indispensable components in modern hydraulics. Their robust construction, ability to generate high pressures, and versatility make them the first choice for a wide range of applications in industry and the mobile sector. By complying with relevant standards and through careful maintenance, they ensure the reliable and efficient operation of hydraulic systems. Continuous development, particularly in the field of internal gear pumps, helps to steadily expand their performance capabilities and range of applications.