Hydraulic hose is specifically designed to convey hydraulic fluid to or among hydraulic components, valves, actuators, and tools. It is typically flexible, often reinforced and usually constructed with several layers of reinforcement since hydraulic systems frequently operate at high or very high pressures. Hydraulic hose is used in a wide variety of industrial hydraulic systems. Dimensions, performance specifications, materials, and features are all important parameters to consider when searching for hydraulic hose.

Construction

Like most industrial hoses, hydraulic hoses are constructed of three basic components: the tube, reinforcement, and cover.

Image Credit: Gates Corporation

Tube -- A plastic or rubber tube or inner lining which makes contact with the fluid.

Reinforcement -- A textile, plastic, or metal body or carcass which reinforces the structure of the hose to withstand internal and external pressures. Reinforcement is key to hydraulic hose because it ensures the hose can withstand the associated high pressures. Types of reinforcement include wire braid and wire spiral.

• Wire braid reinforcement (labeled W on datasheets) typically offers more flexibility, but is much more susceptible to failure under high impulse applications.
• Wire spiral reinforcement (labeled S on datasheets) typically offers more strength, but suffers from increased stiffness and the minimum bend radius. Some new spiral hose technologies overcome the inflexibility problem.

Cover -- A rubber, plastic, metal, or textile cover which protects against damage due to wear, abrasion, and the environment.

There are a number of different hose designs based on the type of braiding or weave structure and the number of layers of material.

Dimensions

Sizing is the most basic and essential factor in hydraulic hose selection. Sizing specifications for hydraulic 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, and system damage. The chart below provides a reference for dash numbers (hose size abbreviations) and their corresponding hose sizes in inches.

Sizing chart for hose I.D. Table Data Credit: Parker

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 industrial hose to appropriate fittings and system components.

The length of hydraulic 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.

Performance Specifications

Important hydraulic hose performance specifications include temperature rating and pressure rating.

Temperature

Hydraulic hoses often operate at temperatures into the hundreds of degrees Celsius, and those that do require temperature ratings which exceed the temperature limits of the application. These limits include both the media temperature (the temperature of the hydraulic fluid) and the ambient temperature (the temperature of 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 type of hydraulic fluid being conveyed can also increase or decrease the effects of temperature variation on the hose, based on the fluid's thermal stability and heat capacity. Because of this, some manufacturers specify different temperature ratings for different fluids.

Pressure

The pressure rating defines the force per unit area that can be exerted on the hydraulic 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. Often manufacturers will incorporate a safety factor into the maximum working pressure ratings of their hoses. Because hydraulic hoses typically operate under high pressures, pressure rating is incredibly important in the selection process for safe and reliable 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.

Materials

Hydraulic hoses and 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.

• Elastomeric or rubber hydraulic hoses are typically lower pressure hoses often selected for their excellent flexibility.
• Fluoropolymer hoses offer excellent flex life in impulse applications, superior chemical and corrosion resistance, and high temperature operation.
• Thermoplastic hydraulic 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.

Features

Hydraulic hoses may incorporate different features based on construction or specific application needs.

• Lay-flat - Lay-flat hose is designed to default to a flat, collapsed (not rigid) structure when not filled with fluid. This feature makes hose easier to store, and more flexible and forgiving while in service.
• Anti-static - Hoses are conductive or semi-conductive to prevent the buildup of static electricity.
• Flame resistant - Hoses are constructed to maintain their integrity in the presence of flame or fire.

Standards

A number of industry standards exist which set requirements for the construction and performance of hydraulic hoses used for different applications. Organizations that provide hose standards include SAE (Society of Automotive Engineers), EN (European Norm), DIN (Deutsche Institute fur Normung), and ISO (International Standards Organization). Specific standards for hydraulic hose include SAE J517 and EN 856.

References

Hose Reinforcement Matters - Hose & Fittings, Etc.

Image credits:

Grainger Industrial Supply | Parker Hannifin | CEJN Industrial Corporation