Hydraulic Block

A hydraulic block, also known as a valve block or control block, is a solid metal component with holes and channels machined into it to guide hydraulic fluid. It serves as a central distribution and mounting unit for valves and other hydraulic components, which are screwed directly onto its surface. In this way, the hydraulic block replaces a network of individual pipes and connects the components to one another via internal channels.

Basics and Structure of a Hydraulic Block

The hydraulic block forms the structural and fluid-dynamic backbone of many hydraulic systems. Instead of establishing each connection between the pump, valves, and actuators with individual pipes or hoses, the block integrates all flow paths within its interior. Design engineers mount the hydraulic components directly onto the machined surfaces of the block, where they communicate with the internal channels via standardized connection patterns.

Drilling pattern and channel routing

The drilling pattern describes the arrangement and path of all holes within the hydraulic block. Each hole represents a channel that carries pressure oil, return oil, or leakage oil. Where channels cross or meet, intersections occur. These intersections must be carefully planned, as unfavorable geometries lead to flow turbulence and pressure losses. Design engineers ensure that channels are dimensioned with sufficient cross-sectional area and that transitions are as straight as possible. Deep bores often end with threaded plugs that remain accessible from the outside to allow for the use of vent or test ports when necessary.

Mounting surfaces and connection diagrams

The surface of the hydraulic block features mounting surfaces for valves, throttles, check valves, or pressure relief valves. These surfaces are milled and drilled according to established standards to ensure compatibility with components from different manufacturers. The connection diagrams define the position of the pressure, working, and return ports as well as the mounting holes. Compliance with these standards ensures interchangeability and simplifies assembly.

Types of Hydraulic Blocks

Hydraulic blocks can be divided into several types based on their design, each of which meets different requirements for flexibility, space requirements, and pressure load.

Monoblock design

In a monoblock design, the entire circuit is integrated into a single block. All channels, valve seats, and connections are combined in this single component. This design is characterized by high mechanical strength and compactness. It is suitable for applications with limited installation space and high operating pressures, where the circuit layout is fixed and no subsequent expansion is required. However, changes to the circuit require a new block.

Sandwich and intermediate plate design

In the sandwich design, engineers stack individual plates on top of one another, with each plate carrying a valve or a function. Intermediate plates connect adjacent valves to each other in terms of fluid flow. This modular design allows the hydraulic block to be expanded or functions to be replaced at a later date without having to remanufacture the entire block. The valves are arranged in longitudinal or vertical chains. CETOP valves according to ISO 4401 are specifically designed for this construction method.

Custom Special Blocks

For complex or unusual requirements, manufacturers produce custom hydraulic blocks. These custom blocks often combine elements from monoblock and sandwich designs and additionally integrate screw-in valves, threaded connections, or sensor mounts at individually specified positions. Although the design effort is greater, the block can be optimally tailored to the system.

Standardization and Interfaces

The standardization of mounting surfaces and connection diagrams is crucial for the compatibility of hydraulic blocks and the valves mounted on them.

ISO 4401 and CETOP

ISO 4401, historically also known as CETOP RP 121H, defines the standardized mounting surfaces for directional control valves. The standard specifies hole patterns, bore diameters, and port designations. Common sizes are NG 03 (CETOP 03), NG 05 (CETOP 05), and NG 06 (CETOP 06). The port designations follow a uniform scheme: P stands for the pressure port, A and B for the working ports to the consumer, T for the return, and Y for drain oil. This standardization makes it possible to combine valves from different manufacturers on the same hydraulic manifold.

DIN 24340 and other standards

DIN 24340 supplements ISO 4401 with additional details regarding valve connections and sizes. DIN ISO 4413 applies to the safety requirements for the entire hydraulic system in which the hydraulic block is installed. This standard regulates aspects such as pressure limitation, leakage monitoring, and emergency shutdown, which also influence the design of the block.

Materials for hydraulic blocks

The choice of material depends on the operating pressure, the environment, and the weight requirements of the application.

Aluminum blocks are primarily used in mobile applications where weight is a factor. Steel and cast iron blocks dominate in stationary industrial applications, where pressures of 350 bar and higher are common. Stainless steel is reserved for special applications, such as in seawater desalination or the chemical industry.

Manufacturing of hydraulic blocks

The manufacturing of a hydraulic block requires precision, as the internal channels must be precisely positioned and drilled without interference.

CNC machining

Conventional manufacturing is carried out on CNC-controlled drilling and milling machines. Starting from a solid block of material, the machines drill the channels in multiple axes, cut threads, and mill the mounting surfaces. Deep drilling places special demands on tool guidance and cooling lubrication to ensure dimensional accuracy and surface quality. At intersections, designers use threaded plugs that remain accessible from the outside and seal the channels.

Additive Manufacturing

Additive manufacturing opens up new possibilities for the hydraulic block. Instead of drilling channels into solid material, the printing process builds up the channel structure layer by layer. This allows for curved and branched channels without intersections and without plugs. According to reports, this can reduce block volume by more than 50 percent, as no straight holes or access holes are required. Additive manufacturing is currently best suited for smaller blocks and special applications, as the available sizes and material selection are still limited.

Design Rules and Pressure Loss Minimization

A well-designed hydraulic block minimizes pressure losses caused by friction, bends, and changes in cross-section within the channels. Designers follow several principles:

• Adequate channel cross-sections: The diameters of the bores must be designed for the maximum flow rate. Cross-sections that are too narrow increase the flow velocity and thus the friction losses.
• Short and straight paths: Every change in direction creates flow resistance. The channel routing should therefore be as direct as possible and have few bends.
• Smooth surfaces: The surface roughness of the drilled ducts affects friction. CNC-drilled ducts achieve Ra values below 0. 8 µm, which is sufficient for most applications.
• Shallow intersection angles: Where channels intersect, shallow transition angles reduce turbulence. Designers avoid right-angle intersections whenever the installation space allows.
• CFD simulation: Flow simulations help identify and resolve bottlenecks and dead zones in the bore pattern early on, before the block is manufactured.

Applications of hydraulic blocks

Hydraulic blocks are used in nearly all areas of fluid technology where multiple valves must be connected in a compact and leak-proof manner.

• Mobile machinery: Excavators, cranes, wheel loaders, and tractors use hydraulic blocks to accommodate the multitude of control valves in a space-saving manner. Aluminum blocks are preferred here due to their lower weight.
• Presses and injection molding machines: In plastics processing and metal forming, hydraulic blocks control the complex cycles of closing, pressing, and opening. Pressures often range from 280 to 350 bar.
• Machine tools: On CNC milling machines and lathes, hydraulic blocks control clamping devices, tool changers, and cooling lubricant circuits.
• Marine and offshore engineering: Here, stainless steel blocks are used that withstand corrosive marine environments and control steering gear, winches, and deck cranes.
• Steel and metallurgical plants: In rolling mills, hydraulic blocks operate at high temperatures and pressures to control rolling stands and conveyor systems.

Maintenance and Servicing

A hydraulic block itself has no moving parts and is therefore generally low-maintenance. Nevertheless, there are aspects that operators must keep an eye on.

Leakage and Plugs

The threaded plugs that seal the cross-drilled holes can loosen due to vibrations or become leaky due to aging. Regular visual inspections for oil leaks at the plug locations are part of routine plant inspections. In the event of leaks, plugs can be tightened or replaced without removing the block.

Oil purity

The internal channels of a hydraulic block are difficult to access after manufacturing. Contaminants that enter the channels during assembly or due to oil aging can impair the performance of the mounted valves. Effective oil filtration and adherence to the recommended oil change intervals are therefore also critical for the service life of the hydraulic block.

Corrosion protection

In blocks made of aluminum or steel without a surface coating, condensation on the outer surfaces can lead to corrosion, which attacks the sealing surfaces over time. A suitable surface coating or paint finish protects the block and maintains the dimensional accuracy of the mounting surfaces.

Development Trends

The development of hydraulic blocks is shaped by several trends. Additive manufacturing enables increasingly complex channel geometries that cannot be produced using conventional drilling techniques. The integration of sensor mounts directly into the block allows for the measurement of pressures, temperatures, and flow rates at central locations without the need for additional connection points. At the same time, digitalization is driving the use of CFD simulation and automated drilling pattern generation, which shortens design time and improves the fluid dynamics performance of the blocks. HK Hydraulik supports these developments with a broad portfolio of standard and custom blocks that can be adapted to changing requirements.