Lesson 1 of 5 · Construction
How a hydraulic hose is built
Every hydraulic hose has three parts: an inner tube that holds the oil, reinforcement that holds the pressure, and a cover that protects both.
The three layers
The inner tube is the layer in contact with the oil. It is a synthetic rubber, most often nitrile, chosen to resist the fluid. Its inside diameter is the size of the hose.
The reinforcement is what makes a hose a pressure hose. It is one or more layers of high-tensile steel wire, or textile on low-pressure hose, wound around the tube. The number and style of these layers set the pressure rating.
The cover is the outer rubber layer. It protects the wire from abrasion, weather, ozone and oil. The information printed along it, called the layline, identifies the hose.
Braided hose
In a braided hose the wires are woven over and under each other in a criss-cross pattern, like a basket. A hose with one layer of braid is called one-wire; with two layers, two-wire.
Braided hose is flexible and bends to a tight radius. It is the standard choice for medium and high pressure up to about 1 in bore. Its limit is impulse: where the wires cross they rub against each other every time the pressure pulses.
Spiral hose
In a spiral hose the wires are laid side by side in a helix, one layer wound clockwise and the next anticlockwise, with rubber between layers. Spiral hoses have four or six layers and are called four-spiral or six-spiral, or four-wire and six-wire.
Because the wires do not cross, spiral hose survives far more pressure cycles and holds higher pressure, especially in large bores. The cost is stiffness: it is heavier, harder to bend and needs a larger bend radius.
Braid or spiral: how to tell
- Cut end: braid shows a woven mesh; spiral shows separate rings of parallel wires.
- Feel: spiral hose is noticeably stiffer and heavier for the same bore.
- Layline: braided types include 1SN, 2SN, R1, R2, R16, R17. Spiral types include 4SP, 4SH, R12, R13, R15.
- Position on the machine: main pump, boom and travel lines on large machines are usually spiral; pilot, return and auxiliary lines are usually braided.
What "four-layer" and similar shop terms mean
Workshops often describe a hose by its number of wire layers and its bore, for example "two-wire half-inch" or "four-layer three-quarter". One and two layers mean braided hose. Four and six layers mean spiral hose. The bore is given in inches, in dash size or in DN.
These descriptions say how the hose is built but not which standard it meets. Two four-spiral hoses of the same bore can have different pressure ratings, so the standard on the layline still matters.
Frequently asked questions
What are the three parts of a hydraulic hose?
The inner tube, which carries the fluid; the reinforcement, which is steel wire or textile and holds the pressure; and the cover, which protects the hose from damage and weather.
What is the difference between braided and spiral hydraulic hose?
Braided hose has wires woven across each other in one or two layers. Spiral hose has four or six layers of wires laid side by side in alternating directions. Spiral handles higher pressure and more pressure cycles; braided is more flexible.
What does two-wire hose mean?
A hose with two layers of steel wire braid. It corresponds to SAE 100R2 or EN 853 2SN and is the common high-pressure hose on mobile equipment.
Why does spiral hose last longer under impulse?
In a braid the wires cross and rub at every pressure pulse, which fatigues them. In a spiral the wires lie parallel with rubber between layers, so they do not wear on each other.
Useful with this lesson
- Unit and dash-size converter
- Find hose length and fittings by machine model
- Hydraulic fitting types and how to identify them
- How to make a hydraulic hose assembly
Ratings and dimensions here are the nominal values set by the standards. The layline and data sheet of the actual hose take precedence.