Mannesmann Rexroth

Mannesmann-Rexroth was a leading manufacturer of hydraulic components and drive technology that emerged from the Rexroth iron foundry in Lohr am Main, founded in 1795. Starting in the 1950s, the company developed into one of the most important suppliers of standardized hydraulic components for industrial and mobile applications. From 1976 to 2001, Rexroth was wholly owned by Mannesmann AG and subsequently merged with Bosch’s automation technology division to form Bosch Rexroth AG, now one of the world’s largest companies for drive and control solutions.

Origins and Entry into Hydraulics

The roots of Mannesmann-Rexroth date back to the late 18th century. In 1795, the Rexroth family took over the water-powered drop hammer in the Elsava Valley in the Spessart region, thereby laying the foundation for a corporate history that, over two centuries, would evolve from an iron foundry into a global leader in hydraulics. In 1850, Rexroth acquired the Steinsche iron foundry in Lohr am Main, which remains a company location to this day and later became the headquarters of Bosch Rexroth.

From Casting to High-Pressure Hydraulics

In the 1930s, Rexroth developed a new cupola furnace that enabled the production of particularly dense and pressure-resistant specialty cast iron grades. This technological innovation was a decisive step toward the company’s later entry into the hydraulics industry, as high-pressure-resistant castings formed the basis for reliable hydraulic housings and assemblies. After World War II, Rexroth initially rebuilt its production with household items such as cookware and irons, thereby laying the financial foundation for its later specialization.

Systematic Development of the Hydraulics Division

Around 1952, Rexroth began manufacturing standardized hydraulic components. In 1954, the company presented its new line of hydraulic products at the Hannover Messe, which is considered its official entry into the hydraulics industry. From that point on, Rexroth systematically expanded its hydraulics business into a second pillar alongside the foundry. The standardized valves, cylinders, and pumps made it possible for the first time to create modular hydraulic systems that could be used in a wide variety of machines and equipment.

Acquisition by Mannesmann and Expansion

In the late 1960s, Mannesmann AG—originally a steel tube manufacturer—sought to diversify its business activities. In 1968, Mannesmann initially acquired 50 percent of the shares in G. L. Rexroth GmbH, then Germany’s leading manufacturer of hydraulic components. In 1975, Mannesmann acquired the remaining shares from the Rexroth founding family and integrated the company into the group as a wholly owned subsidiary in 1976. This gave rise to the Mannesmann-Rexroth brand, which became synonymous with high-quality hydraulic and drive technology in the decades that followed.

Strategic Acquisitions in the Hydraulics Sector

Under the Mannesmann umbrella, Rexroth expanded its expertise through targeted acquisitions. A particularly important acquisition in 1972 was the takeover of Hydromatik GmbH in Elchingen, a specialist in axial piston pumps and axial piston motors. These pumps and motors form the heart of many hydrostatic drives and are known worldwide today under the designations A10V, A4VSO, and A11VO. The axial piston pumps of the A10V series cover a wide range of mobile and industrial applications, while the A4VSO series is designed for high-pressure applications up to 400 bar in presses and heavy industry.

Other significant acquisitions included Brueninghaus, a manufacturer of axial piston motors, and, in 1965, Indramat GmbH, which contributed electrical drive and control technology. Through this combination of hydraulics, electric drives, and control technology, Mannesmann-Rexroth became a multi-technology provider capable of supplying complete drive systems from a single source.

Development of a Full Product Range in Hydraulics

By the end of the 20th century, Mannesmann-Rexroth had built up a nearly complete range of hydraulic products. The portfolio included:

• Axial piston pumps and motors for open and closed circuits, used in presses, injection molding machines, and mobile machinery
• Radial piston pumps and motors for applications requiring high torque at low speeds, such as in winches and conveyor belts
• Vane pumps for applications requiring low pulsation and a steady flow rate
• Hydraulic valves of all types, including directional control valves, pressure control valves, flow control valves, and cartridge valves
• Hydraulic cylinders for industrial and mobile applications
• Hydraulic power units and complete systems for industrial and mobile applications

Hydraulic Innovations at Mannesmann-Rexroth

The Mannesmann-Rexroth era was marked by a series of technological innovations that had a lasting impact on the hydraulics industry. In particular, the integration of hydraulics and electronics was a recurring theme that the company championed early on.

Servo Valves and Proportional Valves

Mannesmann-Rexroth expanded the production of servo valves into a core product line. These high-performance valves enabled precise control of position, speed, and force in presses, test benches, and machine tools. In the 1990s, proportional valves were added, allowing for stepless control of pressure and flow rate via electrical signals. Valves in the 4WRPEH series, for example, offered continuous, analog control for the first time and were thus a prerequisite for controlled hydraulic axes in automation technology.

Electrohydraulic Control Systems

The integration of Indramat control technology with Rexroth hydraulics led to the first electrohydraulic control systems, which combined hydraulic power with electronic precision. Electronic controls drove proportional valves and enabled coordinated motion sequences, such as synchronized press axes or clamping units on injection molding machines. These developments laid the foundation for CNC-controlled hydraulic systems.

Load Sensing and LUDV in Mobile Hydraulics

In the field of mobile hydraulics, Mannesmann-Rexroth was among the first suppliers to introduce load-sensing systems. These systems adjust the pump’s delivery pressure to match the highest load pressure at any given moment, thereby reducing energy consumption. LUDV (Load-Independent Flow Distribution) technology additionally ensured load-pressure-independent flow distribution, which improved control precision and efficiency, particularly in excavators and wheel loaders. In combination with axial piston pumps from the A10VO and A11VO series, as well as valves such as the SX14, this technology became the industry standard.

Transition to Bosch Rexroth

In 1998, Mannesmann converted Rexroth GmbH into a stock corporation to prepare the company for strategic moves. Following Vodafone’s acquisition of Mannesmann and the subsequent divestiture of its industrial holdings, Robert Bosch GmbH acquired the hydraulics and drive technology business. On May 1, 2001, Mannesmann Rexroth AG merged with Bosch’s automation technology division to form Bosch Rexroth AG. As a result, Mannesmann-Rexroth’s expertise in hydraulics and drive technology was consolidated into a single company positioned as a global systems supplier for drive-and-control solutions.

Continuing the Hydraulics Tradition

The product portfolio established under Mannesmann-Rexroth continues to form the foundation of Bosch Rexroth’s hydraulic business to this day. The A10V, A4VSO, and A11VO axial piston pump series have undergone continuous further development. Valve platforms such as the M4 valve block system and compact directional control valves of the RM series trace their origins to developments from the Mannesmann-Rexroth era. The tradition of combining hydraulics and electronics has also been carried on, for example with the Sytronix platform, which enables variable-speed pump drives with energy savings of up to 80 percent compared to constant-speed units.

Significance for the Hydraulics Industry

Mannesmann-Rexroth has had a decisive influence on industrial and mobile hydraulics. The standardization of hydraulic components, which began in the 1950s, made modular system design possible for the first time, providing machine builders and plant operators with flexibility in configuration. The development of axial piston pumps through the Hydromatik subsidiary set standards for power density and efficiency that remain valid to this day.

The early integration of electronics and hydraulics—initiated by the acquisition of Indramat and developments in proportional and servo valves—was another milestone. It laid the foundation for the electrohydraulic systems that are now standard in nearly all demanding hydraulic applications. Plant operators and designers continue to benefit from this legacy today when specifying hydraulic components that offer both mechanical performance and electronic controllability.

Specialized companies such as HK Hydraulik regularly work with components that carry on the Mannesmann-Rexroth tradition, whether in the maintenance of existing systems or in the servicing of axial piston pumps and valves whose design principles date back to that era.

Timeline of Key Milestones