Current hydraulic hose line standards

The hydraulic hose lines used in machines and installations are indispensable in many applications. However, ever higher temperatures, working pressures, compact and complex mounting conditions and extended machine times are leading to ever greater stresses on hose lines in the hydraulic system. Manufacturers of hydraulic hose lines are having to face up to these increasing demands.

In all applications and operating conditions of a system or machine, the safe and reliable operation of hydraulic hose lines is crucial for operators. For this reason, manufacturers of hydraulic hoses are continuously working on improving the properties and thus the reliability and endurance of their products. A central component of this is the pressure-related development of the hydraulic hose. What has changed in the relevant standards over the past few years?

The installation situations for hydraulic hose lines are becoming tighter and tighter, especially in mobile hydraulics. In order to nevertheless ensure safe installation in line with requirements, hydraulic hose lines with narrow bending radii are in increasing demand. A comparison of two multi-spiral hose types with an inner diameter of 25 mm demonstrates the latest developments in the field of compact hose types: Whereas at an operating pressure of 420 bar, the high-pressure hose in accordance with SAE 100 R15/ ISO 3862 with four spiral inserts made of high-tensile steel wire still had a minimum bending radius of 330 mm, in the new generation of hydraulic hoses, this is already far less than half. At the same operating pressure, the compact hose in accordance with ISO 18752-CC with four spiral wire inserts and maximum strength only has a minimum bending radius of 150 mm - an immense advance.

There have been similar major changes in hydraulic hoses for medium pressure ranges. Like all hydraulic hose lines, these must be subjected to a pressure pulse test in accordance with DIN EN ISO 6803. For manufacturers, the test is a prerequisite for being allowed to produce hydraulic hose lines in accordance with requirements and to receive the relevant approvals. It also serves as proof of the functional safety of the components. The latest innovations show that the requirements for this proof of system testing have long been a common basic requirement and are already exceeded in many cases by good-quality hydraulic hose lines. An example of this is the 2SN hydraulic hose in accordance with DIN EN 853 and its further development in the form of the 2SC compact hose type with two braided inserts made of high-tensile steel wire. Where the standard 2SC has to withstand at least 200,000 impulse cycles in the pressure impulse test in accordance with DIN EN 857, the new version sets a remarkable new benchmark. This hose type has been pulse-tested with up to 1 million cycles, is characterised in all nominal widths by an even smaller bending radius than its two predecessors (2SN, 2SC) and the permissible operating pressure also far exceeds the requirements of the standard.

Thanks to the improved parameters, hydraulic hose lines can be used to solve the demanding tasks of energy transmission in hydraulic systems more and more safely and economically. However, the advantages of these numerous further developments only really come into their own if the hose fittings are also taken into account. This is because they are an integral part of a hydraulic hose line assembly and thus crucial to its performance. It often happens that the hydraulic hose and the fitting have different operating pressures. The lower operating pressure is decisive for the marking and the maximum possible pressure load. This can mean that a specific hydraulic hose can be used for the desired application, but not the hose fitting – because the fitting is not designed for the increased pressure load. As a result, a different type that fulfils the required conditions must be used.

Operators of machines and systems benefit in several ways from the numerous further developments in hydraulic line technology: cost reductions, more compact installation and uniform product quality are just some of the added value. Added to this are higher safety functions such as minimised risk of confusing the hose fittings at the connection points, which was caused by the fact that, in some cases, the threads of the light and heavy series matched each other.

An example illustrates the role that different operating pressures play in component selection: a hose fitting from the light series with a 24° sealing cone and O-ring (DKOL15) is approved for a maximum operating pressure of 275 bar in accordance with DIN 20066. If this fitting is now combined with the high-performance 2SC compact hose, which has a maximum operating pressure of 350 bar, the finished hydraulic hose line assembly may still only be operated at a maximum of 275 bar. This is because the weakest component is decisive here.

For installation situations with higher operating pressures, hose fittings of the heavy series (DKOS), which are designed for an operating pressure of up to 420 bar, have been used up to now. However, the use of the heavy series can reduce the cross-section of the line, depending on the connection size. In order to close this gap and find a solution to this conflict, manufacturers of hose fittings of the light series made of steel (DKOL and CEL) achieved an increase in the maximum operating pressure in almost all nominal sizes by means of burst and pulse test series. In this way, the combination possibilities for hydraulic hose line assemblies have been expanded many times over.