A hose is a flexible and often reinforced vessel used to transfer fluids from one location to another. Industrial hose covers the broad spectrum of fluid transfer lines, including flow lines for fluids and gases in pneumatic, hydraulic, or process applications, as well as specialized uses in heavy industry such as mining, geotechnical, and construction. Industrial hose is usually application-specific; consultation with hose manufacturers regarding specific applications is typical.
Hoses are constructed using three basic parts:
Although there are innumerable specific hose designs for different applications, there are four basic types of hose construction found in industry:
Sizing is the most basic and essential factor in industrial hose selection. Sizing specifications for industrial 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. It is the most important factor in hose sizing because it 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, and system damage. Hose and fitting sizes are designated using dash numbers or dash sizes. The dash number designates the size in sixteenths of an inch (i.e. -03 is 3/16"), except for SAE 100R5 transportation and refrigerant hose. The chart below provides a reference for dash numbers and their corresponding hose sizes in inches.
Outer diameter (O.D.) measures the entire span of the hose cross section, including the inner tube, reinforcement, and outer cover. The difference between the O.D. and I.D. reveals the thickness of the hose wall. Outer diameter is important for sizing industrial hose to appropriate fittings and system components.
The length of industrial hose defines its maximum reach between end-points. Increasing length can also increase pressure drop in the system, since hose length is a function of head loss due to friction.
The most crucial performance specifications for industrial hose selection are temperature rating and pressure rating.
When determining the required temperature rating, consider both the media temperature (the temperature of the media conveyed inside the hose) and the ambient temperature (the temperature of the environment outside the hose). The temperature rating of the hose should meet or exceed both of these temperatures. Operating a hose at temperatures above or below its rated range can reduce its service life and have a number of other adverse effects on performance (e.g. loss of flexibility, cracking). The type of media being conveyed should also be considered, since different fluids can increase or decrease the effects of temperature variation on the hose. Because of this, some manufacturers specify different temperature ratings for different fluids.
The pressure rating defines the force per unit area that can be exerted on the hose or vessel during operation, typically measured in pounds per square inch (psi). The required maximum working pressure of the hose should be determined based on both the system working pressure and any surge pressures and spikes. The hose's published maximum working pressure should be equal to or greater than the maximum system pressure and any surge pressures or peak transient pressures in the system. Often the maximum working pressure is rated based on a design safety factor (e.g. 2:1, 4:1) to ensure reliability and safe operation.
Selection Tip: The maximum working pressure of a hose assembly system 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.
For effective performance, it is important to ensure the hose is compatible with the media that is being conveyed. This includes compatibility with the inner tube, cover, hose fittings, and o-rings of the hose assembly. Incompatibility can result in corrosion, abrasion, contamination, and other problems which reduce the performance, safety, and service life of the hose. Chemical resistance charts can be used as guides to determine the compatibility of hose materials with different fluids and chemicals. Certain media have specific characteristics that make them suitable for a particular type of hose design or material.
Often industrial hose is rated or constructed for a specific application. Some standard hose types for specific applications include:
For other, less standard uses, hoses should be selected based on the features needed for the application.
Hoses may be constructed in a number of different ways, each of which provides suitability for different applications.
Hoses may possess design features which are essential for certain applications.
A wide variety of industry standards exist which set specific requirements for the construction and performance properties of hoses used in their corresponding fields. Standards include SAE (Society of Automotive Engineers), EN (European Norm), DIN (Deutsche Institute fur Normung), ISO (International Standards Organization).