Internal gear pumps represent one of the most reliable and versatile technologies in the industrial hydraulics landscape. Among the world's leading manufacturers, Bucher Hydraulics has developed over more than thirty years a complete range of pumps that today meets the most diverse needs: from traditional applications to the challenges posed by Industry 4.0 and variable speed drives.
The QX, QXEH, QXEHX, QXM and QXEM series share a common technological base but differ in specific characteristics that make them ideal for different sectors and applications. Understanding these differences means being able to select the most suitable solution for each operational context.
Why choose an internal gear pump
Before analyzing specific applications, it is useful to understand what distinguishes internal gear pumps from other technologies such as vane pumps or piston pumps.
The main advantage lies in the high volumetric efficiency that remains constant even as operating pressure varies. While other pump types tend to lose efficiency as pressure increases, Bucher internal gear pumps achieve values up to 98% and maintain them stable across a wide operating range.
Added to this is particularly low noise levels, achieved thanks to the optimized tooth profile through CAE design and the technology of the one-piece pinion shaft. In Bucher series, noise levels are generally below 75 dB(A), a value that significantly contributes to comfort in industrial work environments.
Technological evolution: from the QX series to the QXEHX
The QX series represents the fifth generation of Bucher internal gear pumps and constitutes the benchmark of the range. Available in six sizes (from 2 to 8) and with displacements ranging from 3.2 to 495.4 cm³/rev, this series covers a pressure range that reaches up to 400 bar in versions for higher pressures.
QX pumps stand out for:
- Volumetric efficiency up to 98%
- Compatibility with HFC, HFD and biodegradable fluids
- ATEX certifications for use in potentially explosive atmospheres
- Low flow and pressure pulsations
The QXEH series: reliability for heavy-duty applications
The QXEH series was developed for applications requiring maximum reliability even under severe operating conditions. The construction with a monolithic pinion shaft ensures minimal pulsations and excellent response during direction changes, a fundamental characteristic for systems with variable speed drives.
This series reaches continuous pressures up to 250 bar and maximum speeds that vary according to size, while maintaining quietness and durability characteristics that make it suitable for intensive duty cycles.
The QXEHX series: the new generation for high speeds
The QXEHX series represents the most recent evolution of Bucher technology and responds to one of the most marked trends in modern industry: the use of variable speed drives to optimize energy consumption.
The main innovations include:
- Maximum speeds up to 6,050 rpm, with a 20% increase compared to the previous generation
- Improved hydrodynamic lubrication for greater operational reliability
- Cavitation resistance even with critical fluids
- Further reduced noise levels
These characteristics make the QXEHX series particularly suitable for new-generation machines that use inverters and brushless motors to modulate flow according to the actual system demand.
The QXM and QXEM series: when bidirectional operation is required
A separate chapter deserves the QXM and QXEM series, specifically designed for applications requiring bidirectional operation, meaning the ability to operate both as a pump and as a motor.
The distinctive characteristic of these series is the symmetrical construction: the high and low pressure zones are identical, as are the two connection ports. This allows reversing the direction of rotation and flow direction without compromising performance or service life.
QXM series: high performance in 2 and 4 quadrants
The QXM series handles pressures up to 400 bar and is used in both open and closed circuits. Direction change occurs in the order of milliseconds thanks to pinion shaft technology, a crucial aspect for applications requiring rapid and frequent reversals.
QXEM series: the version optimized for variable speeds
The QXEM series shares the bidirectional operation characteristics of the QXM but is optimized for use with variable speed drives. Continuous pressure reaches 210 bar and the construction is designed to ensure reliability even at very low or very high rotation speeds.
Application sectors: where bucher pumps are used
The versatility of Bucher internal gear pumps is reflected in the variety of industrial sectors that employ them. Below is an analysis of the main applications with indication of the most suitable series.
Injection molding machines
The plastic injection molding sector requires pumps capable of ensuring precise flow rates, rapid response to load variations and quiet operation. The QXEH and QXEHX series are particularly suitable thanks to their ability to operate with variable speed drives, allowing flow modulation according to the different cycle phases (injection, holding, cooling).
Low noise is a determining factor in this sector, where machines often operate in enclosed environments and for extended cycles.
Hydraulic presses and forming machines
Hydraulic presses used in metalworking, automotive component production and composite material forming require pumps capable of delivering high pressures with great reliability.
The QX series in high-pressure versions (ranges 3 and 4, up to 400 bar) represents the most common choice, while for applications involving bidirectional piston movements, the QXM or QXEM series are used.
Die casting machines
In die casting of light alloys (aluminum, magnesium, zinc), hydraulic pumps must operate in environments characterized by high temperatures and must ensure precision in controlling the injection phase.
Bucher series compatible with fire-resistant HFC and HFD fluids find privileged use here, offering both the safety required by proximity to molten metals and the performance necessary for intensive production cycles.
Machine tools
In the machine tools sector (machining centers, CNC lathes, grinding machines), internal gear pumps feed lubrication circuits, clamping systems and auxiliary movements. Precision and flow consistency are fundamental requirements.
The QX and QXEH series offer the reliability required for continuous operation, while low noise helps maintain acceptable working conditions even in workshops with numerous machines running simultaneously.
Wind turbines
A rapidly growing sector for internal gear pumps is wind turbines, where hydraulic systems manage blade pitch control and braking systems.
The QXEHX series is particularly suited to this application thanks to its ability to operate with variable speed drives and resistance to severe operating conditions, including the vibrations and temperature excursions typical of installations at height.
Elevators and lifting platforms
In the vertical lifting sector, hydraulic pumps must ensure smooth, quiet and safe movements. The QXEH and QXEHX series are particularly well suited thanks to their low pulsations and reduced noise, essential characteristics for installations in residential or commercial buildings.
Compatibility with variable speed drives also allows implementing gradual starts and stops, improving passenger comfort and reducing mechanical stress on components.
Waste compactors
Waste compactors typically operate with short cycles and frequent movement reversals. The QXM and QXEM series with bidirectional operation are the natural choice for these applications, where the ability to rapidly reverse cylinder direction is a fundamental operational requirement.
The robust construction of Bucher pumps also ensures the durability necessary for service involving intense stresses and often difficult environmental conditions.
Technical characteristics common to all series
Regardless of the series chosen, Bucher internal gear pumps share some characteristics that determine their reliability and versatility.
Hydraulic fluid requirements
All series require a fluid with maximum contamination class ISO 4406 20/18/15. Compliance with this parameter is fundamental to ensure the durability of internal components and maintain performance over time.
The use of fluids with anti-wear additives and a load capacity greater than 30 N/mm² according to DIN 51347 standard is recommended. This aspect becomes particularly critical in applications with variable speed drives, where the pump may operate at speeds below 1,000 rpm.
Viscosity and temperature range
The recommended operating viscosity is between 10 and 100 mm²/s, while values up to 300 mm²/s are allowed for start-up. The temperature range varies from -20°C to +80°C for standard NBR seals, extendable to +100°C with the FPM (Viton) seal option.
To ensure maximum durability, it is advisable to keep the fluid temperature within the optimal range of +30°C to +60°C.
Mounting and configuration options
Bucher pumps are available with 2-hole flange according to ISO 3019/1 (SAE) or ISO 3019/2 (metric), with 4-hole flange available on request. The shaft is available in the standard cylindrical version or with SAE splined profile for direct connection to electric motors.
The configuration versatility also extends to the possibility of creating double and triple pumps, combining elements of different sizes on a single drive shaft.
How to select the most suitable series
The choice between the different Bucher series depends mainly on three factors: the required operating pressure, the need for bidirectional operation and the possible use with variable speed drives.
For standard applications with pressures up to 250-400 bar and unidirectional rotation, the QX series offers the widest range of displacements and configurations.
When the application involves the use of inverters or otherwise variable rotation speeds, the QXEH and QXEHX series guarantee optimized performance and greater long-term reliability.
For systems requiring flow reversal or operation as a hydraulic motor, the QXM and QXEM series represent the solution specifically designed for this type of application.
The future of internal gear pumps in industry
The evolution of Bucher internal gear pumps reflects the broader trends in the manufacturing industry: energy efficiency, noise reduction, integration with electronic control systems.
The growing adoption of variable speed drives is pushing toward pumps capable of operating reliably across an ever-wider speed range, maintaining high efficiencies even at partial speeds. The QXEHX series, with its ability to reach 4,600 rpm, represents the most advanced response to this need.
At the same time, the demand for eco-friendly fluids and the need to operate in potentially explosive environments (ATEX certification) continue to guide development toward increasingly versatile and safe solutions.
In this scenario, internal gear pumps confirm their role as strategic components for industrial hydraulics, capable of combining reliability, performance and adaptability to the specific needs of each application.
