Industrial Hydraulics

Industrial hydraulics refers to the use of hydraulic systems in stationary and industrial applications for the transmission of force and energy using pressurized fluids. In contrast to mobile hydraulics, the focus here is on continuous operation, high power density, and precise control. Industrial hydraulics is found in presses, machine tools, injection molding machines, and many other production environments.

Fundamentals and Operating Principles of Industrial Hydraulics

Industrial hydraulics is based on Pascal’s law: pressure in a confined fluid spreads uniformly in all directions. This principle makes it possible to convert small input forces into large output forces. In industrial hydraulic systems, a pump generates pressure, valves control the direction and flow rate, and cylinders or motors convert the hydraulic energy into mechanical work. The closed-loop system of pressurization, control, and power transmission forms the backbone of countless production processes.

Open and Closed Circuits

In industrial hydraulics, designers generally distinguish between open and closed circuits. In an open circuit, the pump draws oil from a reservoir and delivers it through the control valves to the load. From there, the oil flows back into the reservoir. This design dominates most stationary applications because it is simple in construction and easy to maintain. In a closed-loop system, the oil flows directly from the motor back to the pump without passing through a reservoir. Closed-loop systems are used where compact design and high control accuracy are required, such as in speed and torque control systems for rolling mills or test benches.

Distinction from Mobile Hydraulics

Industrial hydraulics and mobile hydraulics share the same physical principles but differ in several key aspects. The following comparison highlights the main differences:

Industrial hydraulics benefits from controlled environmental conditions and can therefore rely on higher complexity and power density. At the same time, reliability requirements are increasing because production downtime incurs significant costs.

Components of Industrial Hydraulics

An industrial hydraulic system consists of several functional groups that must be precisely coordinated with one another. Each component fulfills a specific task within the overall system.

Hydraulic Pumps as the Pressure Source

The pump is the heart of every hydraulic system. It converts mechanical drive energy into hydraulic energy. Various types are used in industrial hydraulics:

• Gear pumps are known for their robustness and low cost. They are suitable for applications with a constant flow rate and moderate pressures.
• Vane pumps offer good suction capacity and a consistent flow rate. They are frequently found in control circuits and low-pressure systems.
• Axial piston pumps achieve high efficiency and can be infinitely variable. They are predominant in applications requiring dynamic flow and pressure control, such as in injection molding machines and presses.

Modern axial piston pumps achieve volumetric efficiencies of over 95 percent and operate at pressures ranging from 250 to 400 bar. Variable-displacement pumps adjust their flow rate to actual demand, which significantly reduces energy consumption during part-load operation.

Hydraulic Cylinders and Hydraulic Motors

Cylinders convert hydraulic pressure into linear motion, while motors convert it into rotary motion. Both components determine the system’s force and motion output. In industrial hydraulics, cylinders with stroke lengths ranging from a few millimeters to several meters are used, for example in presses or lifting tables. Hydraulic motors drive rotary actuators in mixers, winches, or rotating devices. Rotary piston motors deliver high starting torque at low speeds, while axial piston motors are suitable for higher speeds and dynamic control tasks.

Valves and Control Blocks

Valves control pressure, flow rate, and flow direction within the system. Proportional valves and servo valves enable precise, continuous control and serve as the interface between the electrical control system and the hydraulic drive. In modern industrial hydraulic systems, designers are increasingly integrating these valves into compact control blocks that combine multiple functions and reduce piping requirements.

Auxiliary Components

In addition to the main components, auxiliary devices ensure reliable operation:

• Accumulators buffer pressure fluctuations and provide energy for peak loads.
• Filters keep the hydraulic oil free of particles that cause wear on valves and pumps.
• Coolers dissipate excess heat, as the oil temperature should typically be maintained between 40 and 60 degrees Celsius during continuous operation.
• Pressure gauges and sensors provide the measurement data for pressure, temperature, and flow rate that the control system needs for regulation and diagnostics.

Typical Applications of Industrial Hydraulics

Industrial hydraulics is used in nearly all sectors of the manufacturing industry. Applications range from precision control tasks to high-force applications with pressing forces of several thousand kilonewtons.

Machine Tools and Injection Molding

In CNC-controlled machine tools, hydraulic systems provide clamping, feed, and workpiece handling. Injection molding machines require hydraulics for closing the mold, the injection process, and the ejection movement. Fast cycle times and high repeatability are essential here.

Metal Forming and Presses

Hydraulic presses operate with forces ranging from several hundred to several thousand metric tons. They are used in deep drawing, stamping, and forging. The stepless pressure and force control allows for precise adaptation to the respective forming process.

Test Benches and Simulators

Test benches for components, materials, or complete systems use hydraulics to apply defined loads and movements. Servo-hydraulic test benches achieve high dynamics and control accuracy, making them indispensable for fatigue testing and crash simulations.

Other Areas of Application

Other typical applications can be found in steel processing, the paper and wood industries, elevator systems, the petrochemical industry, as well as in automation and robotics. Wherever high forces combined with precise control are required, industrial hydraulics provides the right solution.

Standards and Regulations

The design and operation of industrial hydraulic systems are subject to several standards and guidelines. The key standard is DIN EN ISO 4413, which establishes general rules and safety requirements for hydraulic systems and their components. It is harmonized with the Machinery Directive 2006/42/EC and defines requirements for design, construction, installation, operation, and maintenance.

The following standards also apply:

• DIN EN ISO 12100 for the risk assessment of machinery
• Pressure Equipment Directive 2014/68/EU for pressure vessels and piping systems rated at 0. 5 bar or higher
• DIN 20066 for hose assemblies
• DIN 24550 for hydraulic filters
• DIN 24343 for maintenance checklists for hydraulic systems

The CE marking of a machine with a hydraulic system requires that a risk assessment in accordance with ISO 12100 has been performed and that the Type C standard ISO 4413 has been complied with. Manufacturers must issue an EC Declaration of Conformity and document the measures taken in the technical dossier.

Safety Requirements According to DIN EN ISO 4413

Among other things, the standard requires that all components be designed for the maximum operating pressure, including any surge pressures that may occur. Pressure relief valves must be installed in every circuit and reliably limit the pressure. Pipes and hoses must be sized to withstand pressure surges and routed so that no kinks or chafing points occur. Control systems must ensure safe shutdown in an emergency, and all system components must bear labels with warning notices and operating parameters.

Maintenance and Servicing

The reliability of an industrial hydraulic system depends largely on maintenance. Production downtime incurs high costs, which is why preventive maintenance and condition monitoring are standard practice in the industry.

Oil Quality and Filtration

The cleanliness of the hydraulic oil is a critical factor in the service life of pumps, valves, and cylinders. Particles in the micrometer range can damage the control edges of proportional valves and scratch piston surfaces. Filters with the appropriate filtration rating, checked and replaced regularly, maintain oil quality at the required level. Monitoring oil contamination in accordance with ISO 4406 is part of standard maintenance procedures.

Temperature Management

During continuous operation, hydraulic oil heats up due to power loss. Temperatures above 60 degrees Celsius accelerate oil aging and impair viscosity, which in turn increases leaks and wear. Oil coolers and sufficiently sized reservoirs keep the operating temperature within the permissible range.

Wear Parts and Inspection Intervals

Seals, bearings, and sliding surfaces are subject to wear. Regular inspections in accordance with manufacturer specifications and documentation in accordance with DIN 24343 ensure long-term operation. Hose lines have a limited service life and must be inspected and replaced on schedule in accordance with the requirements of DGUV Information 061.

Trends and Developments in Industrial Hydraulics

Industrial hydraulics is constantly evolving. Energy efficiency, digitalization, and the integration of smart control systems are driving this transformation.

Energy Efficiency and Electrohydraulic Drives

Variable-displacement pumps with speed-controlled electric motors significantly reduce energy consumption during partial-load operation. Servo pump units adjust flow rate and pressure as needed and reduce power loss by up to 50 percent compared to conventional systems with fixed-displacement pumps and pressure valves. This development is gaining importance as energy costs and sustainability requirements in industry rise.

Digitalization and Condition Monitoring

Sensors measure pressure, temperature, flow rate, and oil contamination directly at the components. Bus-compatible connections transmit the data to higher-level control systems and cloud platforms. Condition monitoring detects wear and anomalies early on, before a failure occurs. Predictive maintenance is increasingly replacing time-based maintenance and increasing system availability.

Integration and Modularity

Modern hydraulic power units combine the pump, tank, filter, cooler, and control system into compact, pre-assembled units. This reduces on-site installation effort and improves reproducibility. At the same time, demand is growing for custom solutions that can be seamlessly integrated into existing machine designs.

Industrial hydraulics remains a key technology in production engineering. Its combination of high power density, precise controllability, and robust design makes it indispensable for many applications, and current developments toward efficiency and digitalization ensure its future viability.