Safe management of air compressor hose lines 16 Mar 2021

The problem of connecting hose lines to modern high-pressure air compressors is well known. Following a number of hazardous events and fatal accidents, the industry has developed a high-pressure layflat hose system with dedicated coupling connectors. When using compressed air equipment on site, a clear distinction has to be made. When working at operating pressures of up to 25 bar it is quite acceptable to continue to use tried and tested systems with hose clamp fittings. When working at pressures of up to 40 bar, it is advisable to fit the hoses with hydraulically pressed steel sleeves and matching hosetails, and respect the specified operating temperatures. Hoses with a certain plastic content can be especially prone to significant changes in their material properties at high working temperatures and may begin to flow. This is something that must be avoided at all costs.

This a situation that does not require the drafting of new standards or guidelines. What is important is that users have a basic awareness of the fact that flexible hoses must be used carefully and competently when operating compressed air equipment. This requires that only experienced personnel be employed on work of this kind and that compressed air lines should always be fitted with parts from established suppliers who can provide safety data sheets, assembly instructions and manufacturer warranties.

Modern air compressors are now capable of delivering working pressures that would not have been available a few years ago. The use of air-powered plant and equipment has become routine with the heightened risk of creating dangerous situations and accidents involving personal injury. While some of the problems arising in this area can only be tackled by introducing appropriate on-site measures, the firms A.S.T. Bochum, Gollmer & Hummel and Lüdecke have come together to develop a layflat hose concept with coupling systems that can safely be connected to the latest types of high-pressure air compressors.

Test comparison between a fitting copy (left) and an original quality fitting

Pressure test at 190 bar illustrating potential for hose improvement

Handling high temperatures

Problems often arise when connecting 2in hoses to modern compressors that are designed to operate at pressures of up to 40 bar. In such cases the traditional band clamps that provide troublefree service at operating pressures of up to 25 bar are no longer suitable for the purpose. The high pressures involved generate high heat temperatures, especially at the compressor exit points. Well-proven hose lines, and especially layflat hoses that are generally suitable for such lower pressure levels, can fail under these conditions. The fittings, which are designed to be pressure and heat resistant, can be forced out of the hoses as the hose material is softened by the effect of the heat. Compression connectors are suitable for applications of this kind, though the fitting must be exactly matched to the hose in question, especially when a layflat hose is being used. Moreover, the contours of the hosetail connector must be an exact fit for the hose so that the connection is at all times able to withstand the high pressures and temperatures.

New hose and coupling system

Three companies operating in this field, namely A.S.T. Bochum, a supplier of hoses, fittings and tunnelling equipment; hose manufacturer Gollmer & Hummel; and hose coupling maker Lüdecke, have pooled their expertise to develop a safer hose system. As it was not the pressure and heat resistant fittings that are the problem, but rather the actual hose line, which tended to become softer when exposed to heat, the development team had to focus their efforts on producing a new type of hose system. It was decided that pressing the hose on to the fitting by force was still the most reliable and effective solution and the team set about identifying a better type of hose material.

Problem-free pressure test of a quality hose at 160 bar

Fixing hoses onto pressed sleeves is a job for trained personnel

Silicon hoses exhibit excellent heat resistance, however they have a low pressure rating and this quality cannot easily be improved. Metal hoses, such as exhaust gas hoses, could be made pressure resistant, though these would inevitably become very heavy and stiff. Add to this the fact that each length of hose would have to be braided and manufactured individually. The time expended on this operation and the high cost of such an individualised production process would be unacceptable.

The work of developing a lightweight, heat and pressure resistant layflat hose initially focused on the composition of the hose material with the aim being to ensure a good interaction between the fitting, the hose and the pressed sleeve. The experienced design team also paid increasing attention to developing a practicable press-fitting process that would save time and money. After several trial runs with different hose materials and coupling connectors, the result is a hose system that meets the requirements for pressure and heat resistance.

Application of the newly developed HP layflat hose

Integral couplings for layflat hoses

The new system is suitable for both compressed air and fluids and has been designed for maximum operating pressures of up to 40 bar and temperatures of between -30 to +80 °C. The integral couplings are of a steel and malleable iron material and the high-pressure layflat hose system comes fully-fitted with hosetails and sleeves.

When the pressed sleeves are being fitted during the assembly process, it is important not to exceed the maximum operating pressures specified for the sleeves, couplings and hoses. The process of fitting the sleeves to the hose and spigot must always be performed by qualified personnel using a suitable hydraulic press. The entire hose assembly must be inspected for signs of damage before each use. It is recommended that a protective hose stocking or cable be employed as an additional safety measure.

Initial applications in the field have confirmed that the new hose system is robust and durable and has a high safety factor. The hose itself is light and compact to handle, and highly resistant to abrasion and capable of withstanding the toughest of site conditions. The hoses have now been put under pressure in numerous operations and have performed flawlessly with the entire system delivering a high operating life.