How to Select Air Hose and Air Duct Hose
Air hose and air duct hose is used to transport compressed air, gases, or lightweight bulk solids in air. It is typically flexible and often reinforced. It can be purchased as straight hose or as a complete assembly including all fittings and components for joining and sealing. Air hoses are used as air ducts for heating and cooling, to supply gases for various regulated applications, to supply compressed air at high pressures, and to convey bulk materials such as grain from trucks or rail cars into storage silos.
Sizing is the most basic and essential factor in air hose and air duct hose selection. Dimensions for hose include inner diameter, outer diameter, and length.
Inner diameter (I.D.) is the span of the empty space in a circular hose cross section that affects the flow velocity of the fluid within the hose. A hose with an oversized I.D. will result in sluggish system performance, while an undersized I.D. can cause excessive pressure drops, leaks, or system damage.
Outer diameter (O.D.) measures the entire span of the hose cross section, including the tube, reinforcement, and cover. The difference between the O.D. and I.D. is the thickness of the hose wall. Outer diameter is important for sizing bare hose to fittings and system components.
The length of hose defines its maximum reach between end-points. Hose should be of adequate length to reach all possible points of connection or application. Increased hose length also increases the pressure drop of the system, which can affect corresponding air driven equipment.
Important air hose and air duct hose performance specifications include temperature rating and pressure rating.
Some air hose and air duct hose applications require the flow of high or low temperature air or gas. These applications require hoses with temperature ratings which exceed those of the media (air or other gas) and the surrounding environment. Operating above or below a hose's rated temperature range can reduce its service life and have a number of other adverse effects on performance (e.g. loss of flexibility, cracking).
The pressure rating defines the force per unit area that can be exerted on the air hose or air duct hose during operation, typically measured in pounds per square inch (psi). The required maximum working pressure of the hose should be greater than the working pressure and any surge or peak pressures in the system. For hoses designed for high pressures, manufacturers will often incorporate a safety factor into the maximum working pressure rating to guarantee safe and reliable performance.
Selection Tip: The maximum working pressure of a hose assembly is rated based on the pressure rating of the weakest component in the system. For example, if the hose has a pressure rating of 7,500 psi but a quick-coupler fitting has a pressure rating of only 4,200 psi , the pressure rating for the assembly is 4,200 psi.
Vacuum hose and hose assemblies may also have ratings for minimum pressure or maximum vacuum. These define the minimum vacuum pressure that can be maintained within the hose during vacuum applications.
Air hoses and air duct hose assemblies are frequently constructed of multiple materials, but the primary materials used are of the most importance. These materials differ based on various physical properties.
Elastomers, including rubber, are commonly used to construct low pressure air hoses because of their excellent flexibility and abrasion resistance.
Fluoropolymer hoses offer excellent flex life in impulse applications, superior chemical and corrosion resistance, and high temperature operation.
Thermoplastic hoses offer tight minimum bend radii and excellent kink resistance.
Metal hoses can handle high temperature flow materials and often can handle very high pressures. They can be either stiff or flexible.
Air hoses and air duct hoses may be constructed to incorporate a number of different features which may be important depending on the application.
Anti-static - Hoses are conductive or semi-conductive to prevent the buildup of static electricity.
Coiled - Hose is coiled for flexibility and elasticity, making it expandable and relatively easy to store.
Corrugated - Hose contains corrugations, pleats, or spiral convolutions to increase flexibility and the capacity for compression and elongation.
Crush-proof - Hoses are designed to resist crushing or collapse caused by exterior forces. This is important for applications where flow interruption or kinking could cause serious system damage.
Flame resistant - Hoses are constructed to maintain their integrity in the presence of flame or fire.
Lay-flat - Lay-flat hose is designed to default to a flat, collapsed (not rigid) structure when not filled with fluid. This feature is less common in air hoses and air duct hoses.
Reinforced - Reinforced hoses are constructed with some type of reinforcement that provides additional strength.
A wide variety of industry standards exist which set specific requirements for the construction and performance properties of air hoses used in different applications. Standards include SAE (Society of Automotive Engineers), EN (European Norm), DIN (Deutsche Institute fur Normung), and ISO (International Standards Organization).
Air hose and air duct hose products cover a broad range of applications. In general, however, air hose applications can be divided into three types based on the type of media they convey.
Bulk solids - air hose can be made to carry bulk granular or pelletized solids in an air or gas stream. These tubes must be able to withstand the abrasive action of solids moving through the interior.
Compressed air - air hose can be made for larger pneumatic systems. These vessels must have high strength and strong seals to prevent leaks or damage. When being used with tools and equipment that are oil-lubricated, the hose must be able to resist oil mist corrosion.
Other gases - air hose can be made to carry a wide variety of different gases for heating and cooling as well as industrial, medical, and semiconductor applications. These hoses require resistance to the corrosive nature of the chemicals they transport.
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