Hydraulic Connections for the Design and Expansion of Hydraulic Systems

Hydraulic connections are central components in hydraulic systems. They are used to connect lines, valves, cylinders, pumps, and other components. Hydraulic connections ensure a secure, tight, and maintenance-friendly link between the various elements of a hydraulic circuit. In doing so, they ensure that the fluids—usually hydraulic oil—can be transmitted under high pressure even across detachable connections.

Types and Use of Hydraulic Connections

Hydraulic connections are fundamentally divided into the following two types:

• Permanent
• Detachable

Permanent Hydraulic Connections

Permanent hydraulic connections essentially consist of a simple screw connection with internal and external threads. The screw is hollow inside so that it can pass the hydraulic fluid through. The screw and nut are optionally equipped with a swivel ring. This facilitates installation and makes the assembly of the hydraulic system easier. Once installed, however, the connection remains in place and is only loosened again for maintenance, repair, or replacement.

Other frequently used hydraulic connections include, for example, banjo fittings. They allow for a right-angled transmission of hydraulic pressure without branching. Banjo fittings are used in locations with limited installation space.

Detachable Hydraulic Connections

Detachable hydraulic connections consist of quick-release couplings. They can be disconnected without the use of tools. They are ideal for hydraulically operated equipment that needs to be coupled alternately to the same connection.

In agriculture, these connections are used as standard. With the hydraulic pump on the tractor acting as the pressure generator, all types of hydraulically operated agricultural equipment can be connected in just a few steps.

Threaded couplings are an intermediate solution between detachable and permanent hydraulic connections.

The most important property for hydraulic connections is their ability to withstand hydraulic pressure. Today, even detachable quick-release couplings can easily withstand pressures of up to 1,000 bar. This makes the handling of high-performance systems particularly easy.

Hydraulic connections can be divided into several main categories:

1. Fittings:
   These include cutting ring fittings, flared fittings (e.g., 37° flare according to SAE J514), and 24° cone fittings. They are widely used and enable a reliable, detachable connection. They are ideal for when systems need to be expanded or supplemented. However, they are less suitable for fast and flexible reconfiguration, as their sealing integrity decreases with frequent opening and closing.
2. Flange Connections:
   SAE flanges (e.g., SAE 3000 PSI or 6000 PSI) are used primarily for high pressures (over 300 bar) and high flow rates. They offer high stability and sealing integrity but are mainly designed for permanent use.
3. Plug-in and Quick-Release Couplings:
   These allow for the fast and easy connection and disconnection of lines without tools. They are particularly in demand in mobile applications, such as in agricultural and construction machinery technology. Quick-release couplings are especially popular because of their flexibility. However, they are relatively expensive and not suitable for every pressure level.
4. Pipe and Hose Connections:
   Hoses require suitable hose fittings that are crimped or screwed. Pipes are usually connected via fittings or welded joints. This is a solution for the permanent connection of hose and pipe lines.

Design of Quick-Release Couplings

A hydraulic quick-release coupling must be rotatable, pressure-resistant, and capable of being disconnected and mounted without tools, even under pressure. To achieve this, hydraulic quick-release couplings consist of a very complex mechanism with a large number of individual elements.

The latest systems of this type can couple pressure connections of up to 200 bar without leakage loss. This is an important ecological and economic step forward for industry and agriculture. Integrated ball bearings allow the connections to remain rotatable by 360°. They make the connection of hoses and moving elements significantly easier.

Standards for Hydraulic Connections

To ensure compatibility and safety, hydraulic connections are subject to numerous standards. Important standards include DIN EN ISO 8434, SAE J514, ISO 6162 (for flanges), and ISO 12151 (for hose fittings). These regulate dimensions, sealing systems, and load capacity.
For quick-release couplings in agriculture, for example, the following standards apply: