Air & Gas Hoses - How They Work

NBR air and gas hose

Figure 1: NBR air and gas hose

Air and gas hoses are designed to transfer compressed air and gases from one point to another in industrial, medical, construction and agricultural applications. These hoses are generally made up of materials like NBR (Nitrile Rubber), PVC (Polyvinyl Chloride), EPDM (Ethylene Propylene Diene Monomer), PTFE (Polytetrafluoroethylene), Silicone, etc. Generally, stainless steel or polyester fabric braiding is used as reinforcement in these hoses to ensure safety and longevity. They must also comply to various ISO, EU and US standards for air and gas safety. Figure 1 is an example of an air and gas hose with NBR inner and outer layer.

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Air and gas hoses can typically be differentiated into low pressure hoses and high-pressure hoses. Low pressure hoses are used for gases like acetylene, oxygen, butane/propane mix, natural gas, neutral gas, etc. High pressure hoses are used for pressures above 140 bar and for purposes like gas cylinder filling and emptying.

Table of Contents

Media Type

As the name suggests, air and gas hoses are used for handling gaseous media like compressed air, propane acetylene, etc. Knowing and understanding your media type is important when selecting your hose material and specifications to ensure proper function.

Air

Air hoses are used to convey compressed air for pneumatic systems. These air hoses must have high strength to handle high pressures in order to prevent leakage and damage. In addition, oil-based lubricants are sometimes added to the compressed air for smooth running of the equipment. Therefore, these air hoses must also be oil resistant. To handle the high pressure and oil-based lubricants, rubber is the common material choice for an air hose.

However, in large compressors, air molecules frequently collide with one another generating heat. This can cause excessive heat can degrade rubber hoses, which reduces service life of the hose and causes safety concerns. Therefore, for high temperature applications, a corrugated metal hose must be used. These corrugated metal hoses dissipate the excess heat quickly and help to cool down the media.

Gas

In industrial facilities, the gases that are transported may be toxic and/or flammable. Such applications should give special attention to selecting the right type of hose and their fittings. The gas hoses must be leak proof and resistant to breaking. Misjudgment on the hose materials, pressure requirement and fittings may lead to hose failure, which can be very dangerous in such facilities.

Materials

There is a wide variety of materials available when selecting an air and/or gas hoses suitable for your application. Some of the most commonly used hose materials are discussed below:

Rubber hose

Rubber is the most commonly used materials and is an inexpensive choice (in comparison to other materials) for air and gas hoses. These hoses are strong, flexible, durable and can handle different heat and temperature variations. Rubber compounds like EPDM and NBR also make a great choice for air and gas hoses. EPDM rubber provides great resistance with heat, temperature and ozone. Similarly, NBR is resistant to oil and chemicals. However, rubber cannot provide zero permeability and cannot be used for applications which requires high purity. A high purity gas has low amount of other gases present, making them better quality. Permeable materials may compromise the quality of such gases by picking up contaminants.

PVC hose

PVC is a widely used material for general purpose air and gas hose application. PVC hoses are inexpensive, durable and lightweight. They are lightweight, therefore, practical to use outdoors or at greater heights. However, PVC hoses are inadvisable for use in colder temperature as they are prone to curl or crack in such temperature.

PTFE hose

PTFE (Polytetrafluoroethylene) hoses are suitable for high pressure industrial applications. They are durable, flexible and economical. For applications requiring high purity, PTFE can be exposed to a “post-sintering” process. During this process, the PTFE is processed again at controlled temperature and pressure. This helps in increasing the number of molecular bonds, increasing strength as well as wall thickness of the hose, resulting in reduced diffusion. Diffusion is when gas molecules can easily escape through the pores of the hose due to their smaller molecular weight.

All metal corrugated hose

All metal corrugated hoses are generally used with gases like hydrogen and helium. These gases possess risk of diffusion. All metal corrugated hoses have a metal corrugated inner core. They have zero permeability, so they are not exposed to gaseous diffusion. However, they are costly in comparison to other hoses and are much less flexible.

Silicone hose

Silicone hose

Figure 2: Silicone hose

Silicone hoses are known for flexibility and strength. They can operate in a wide temperature range, making them ideal for heating, cooling and charged-air applications. Figure 2 is an example of a silicone hose.

Hose requirements

Different hose materials exhibit their own properties, so it is important to understand the material properties for your application and media. The following requirements are key for the safe functioning of these air and gas hoses under varying conditions.

Gas diffusion

Generally, hose materials like rubber and PTFE are permeable to some degree. It means, the gas molecules can enter in or escape out through the pores of the hose. When the gas molecules escape through the pores, it results in a pressure drop leading to excessive energy consumption and poor system performance. This outward diffusion of gas is especially hazardous when flammable gases are part of the application. Likewise, other gases may also enter the hoses leading to contamination. An all corrugated metal hose is generally recommended to eliminate the risk of gas diffusion. Post-sintered PTFE hoses are also an excellent alternative to metal hoses.

Chemical stability

Air and gas hoses can be exposed to different types of gases. The hose material should be able to withstand the chemical’s properties. Therefore, it is necessary to select the hose material directly from your application requirements as a hose material may work for certain media and not for others.

Environmental stability

Hose materials like rubber and PVC are not resistant to environmental factors like UV rays and extreme weather. The external environment should be considered while selecting the hose for your application. EPDM, Silicone, ETFE and PTFE are better options when it comes to applications prone to UV rays and extreme temperatures.

Industry examples

Air and gases hoses are used in a wide variety of industrial applications. Scuba divers use these hoses attached to oxygen tank for breathing purposes. Labs and industries also use these hoses for carrying different types of gases or for applications like welding. Some of the more common applications are discussed below:

Welding

Gas hoses are used for various welding applications like assembly, brazing, cutting, fabrication, pre-heating, post-heating, soldering, etc. Rubber hoses are generally used for their strength and flexibility. Gases used for welding applications generally include acetylene, hydrogen, helium, natural gas, propane, propylene, oxygen, etc.

Breathing air

Breathing air hose

Figure 3: Breathing air hose

Air hoses are used in medical and recreational applications for providing breathing air. A standard rubber hose cannot be used for such application as toxic hydrocarbons may enter the respiratory system. Generally, a food grade polymer is used to avoid such potential health hazards. Figure 3 is an example of breathing air hose.

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Additional hose components

The selection of additional components for the hoses should be given equal importance as the selection of the hose. The specifications like pressure of the hose, material type, diameter of the hose, etc. plays an important role in the selection of these additional components for accident prevention.

Hose reels

Automatic hose reel for compressed air

Figure 4: Automatic hose reel for compressed air

Hose reels are designed to provide protection to the hoses. Modern hose reels are retractable and provide complete encasing to the hose. These hose reels also help eliminate loose uncoiled hoses on the shop floor and reduces the risk of accidental damage to the hose.

Pressure Gauge

An air pressure gauge or gas pressure gauge allows the user to know the systems pressure. This is important to ensure the pressure doesnt excceed the aplication requirements or other product specifications.

Hose fittings

Fittings for air and gas hoses should be able to withstand the pressure required for the application to run smoothly and safely. Generally, brass, type 304/316 stainless steel or zinc plated steel are used as the material for the fittings. The material of the fittings should be resistant to the corrosive effect of the gas. Figure 5 is an example of a brass hose connection fitting.

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Hose connection fitting

Figure 5: Hose connection fitting

Standards

Air and gas hoses must meet EU, ISO, FDA and other domestic and international standards considering its wide variety of use from industrial to medical purpose. Review your local standards to ensure compliance. A brief overview of common standards is below:

  • EN 1762:2018 outlines the requirement for rubber hoses and its assemblies for use with liquefied petroleum gas (LPG) in liquid or gaseous state and for natural gas transfer.
  • ISO 2398:2016 provides the specification for textile-reinforced rubber hose for compressed air.
  • ISO 3821:2019 specifies the requirement for rubber hoses used for welding, cutting and braising process.
  • 29 CFR 1910.134 compliance in OSHA emphasizes the respiratory protection. It lists the air hoses safe for breathing purposes approved by The National Institute for Occupational Safety and Health (NIOSH).
  • EN 559: 2003 standard provides specification for rubber hoses for welding and cutting.
  • EN 14593-1:2018 gives an overview on the standards for compressed air line breathing devices.

FAQ

What is an air hose?

An air compressor hose is designed to transport compressed air from one point to another. They are used in a wide range of applications from filling tires to supplying breathing air for medical/recreational purposes. They are typically made from Rubber, PVC, Silicone, EPDM, or Metal.

Does length of an air hose affect pressure?

Yes, due to turbulence created within the hose, which is characterized by the Reynolds number. The more turbulence the higher loss in pressure. To minimize a loss in pressure, the coefficient of friction of the inner hose can be optimized as well as the length minimized.

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