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The Basics
What is a hydraulic hose?
A tube that carries oil at pressures which would turn ordinary hose inside out, while bending thousands of times a day. Everything about how it is built follows from those two demands, and reading one tells you most of what you need to know.
- Three layers. A tube that suits the fluid, reinforcement that holds the pressure, a cover that protects the reinforcement.
- The reinforcement is the hose. Braid flexes better, spiral holds more pressure and impulse.
- The layline tells you what it is. Specification printed along the cover, repeated every foot or so.
- It is an assembly, not a hose. What you actually need is cut to length with fittings crimped on both ends.
- Working pressure, not burst. Burst is a test figure roughly four times working, and it is not a target.
- A pinhole leak at working pressure goes through skin. Never search for one by hand.
The basicsWhat makes it different from other hose
Hydraulic systems work because liquid does not compress. Push on it in one place and the pressure appears everywhere at once, so a small piston at a pump becomes a large force at a cylinder. That is how a machine of modest engine size lifts several tonnes.
What makes hydraulic hose a distinct product is the combination it has to manage. It contains oil at thousands of psi, and it has to bend while doing it. Pipe would hold the pressure easily. Rubber tube would bend easily. Hydraulic hose has to do both, thousands of times a shift, for years.
Every other component in a hydraulic system is rigid and bolted down. The hose is the only one asked to move. That is not a design flaw, it is the job, and it is why hoses are consumable while pumps are not.
ConstructionThree layers, three jobs
The tube
The innermost layer, and the only one that touches the fluid. It has to be chemically compatible with whatever is running through it. Nitrile for petroleum-based hydraulic oil, which covers most equipment. Different compounds for water-glycol, fire-resistant and biodegradable fluids, and PTFE where the chemistry is aggressive or the temperature is extreme.
The reinforcement
High-tensile steel wire, braided or spiral wound, and this is what actually holds the pressure. How many layers there are and how they are laid decides the rating. Everything else is support.
The cover
Protects the reinforcement from moisture, abrasion, ozone and impact. It looks cosmetic and is not: once the cover is through, the wire underneath starts corroding, and the hose is on borrowed time even though nothing is leaking.
That is why a scuffed cover matters. People treat it as damage to the outside of the hose. It is actually the loss of protection for the part that does the work.
TypesBraid, spiral and thermoplastic
| Construction | What it suits | Trade-off |
|---|---|---|
| Single wire braid | Moderate pressure general hydraulics | Lowest rating of the wire types |
| Double wire braid | The fleet and equipment workhorse | Stiffer than single braid |
| Spiral wire | High pressure and high impulse cycling | Considerably stiffer, larger bend radius |
| Thermoplastic | Light, flexible, twin line and mobile equipment | Different handling and repair characteristics |
| PTFE with stainless braid | Extreme temperature and aggressive chemicals | Cost, stiffness and bend radius |
The braid versus spiral distinction is the one that matters most in practice. Braid flexes more readily, spiral handles more pressure and more pressure cycling. A boom circuit that bends constantly and a main supply line that barely moves want different constructions even at the same rating.
There is also a suction and return category, built with a helix to resist collapse under vacuum rather than to hold pressure in. Different problem, different hose.
The useful skillReading a layline
The hose tells you what it is
Properly made hydraulic hose carries its specification printed along the outside, repeated every foot or so. Learning to read it is the single most useful thing anyone working around hydraulics can pick up, because it removes guesswork entirely.
- Standard
- Such as SAE 100R2, telling you the construction and its performance class
- Size
- The bore, often as a dash number, where each dash is a sixteenth of an inch
- Working pressure
- The continuous operating pressure it is rated for, not the burst figure
- Manufacturer
- Whose hose it is, which matters because fittings must come from the same system
- Date or batch
- Often present, and useful for judging age on an unknown machine
If a hose carries no layline at all, nobody can verify what it is. That is a reason to replace it rather than a detail to overlook. Standards behind the marking are in SAE J517.
The distinctionHose versus assembly
Worth being precise about, because it causes confusion at the counter constantly.
A hose is the flexible tube on a reel, sold by the foot. An assembly is what your machine actually needs: that hose cut to length with fittings crimped onto both ends, at the correct orientation, tested and ready to fit.
The crimp is not a detail. It is a ferrule compressed by machine to a measured finished diameter, matched to a chart published for that specific hose and fitting pairing. Under-crimped and the fitting blows off under pressure. Over-crimped and the ferrule has cut into the reinforcement it was meant to grip. Both look identical from outside.
A failed assembly carries the bore, the construction, both fittings and the orientation between them. That is nearly the whole specification, sitting on the counter, and it works on equipment nobody supplies parts for any more.
PressureTwo numbers, and the one in between
Working pressure is the maximum continuous operating pressure the hose is rated for, and it is the number to specify against. Burst pressure is where it fails on a test rig, typically around four times working. Burst is a manufacturing benchmark rather than a capability, and quoting it as one is how systems end up under-specified.
Neither accounts for surge. Every time a valve closes quickly the pressure spikes above working, and on a machine cycling constantly those spikes are relentless. That is why impulse resistance is a real specification and why a hose that is correct on steady-state pressure can still fail early.
SafetyThe one rule to take away
Never search for a hydraulic leak with your hand
At working pressure a pinhole leak produces a jet fine enough to be invisible and strong enough to go through skin. The entry wound looks trivial. Hydraulic fluid in tissue is not, and hand surgeons treat these as surgical emergencies where delay leads to amputation.
Use a piece of cardboard held at arm's length. Depressurise before working on anything, and remember that circuits hold pockets of pressure after the engine stops. Industry guidance on the technique is in this toolbox talk on high-pressure injection injuries.
If it happens, go straight to a hospital emergency department, say the words high-pressure injection injury, and take the fluid safety data sheet.
Going deeperWhere to read next
This covers the ground floor. Each of these takes one part of it considerably further.
At the counterWhat we build
Hydraulic assemblies from 1/8 inch to 2 inch, up to 6,000 psi, braid through spiral, crimped on calibrated equipment to the manufacturer's chart.
- Built from your old assembly, so no part number is needed.
- Matched hose and fittings from the same system, because the crimp chart depends on it.
- Construction chosen for the circuit rather than whatever is nearest on the rack.
- Specification kept on file, so the next one for that machine is quicker.
Most are finished the same visit at either counter. See hydraulic hoses, hydraulic hose assemblies and crimping.
Proudly serving Long Island since 1964
Sixty years building hydraulic assemblies for Long Island fleets, contractors and shops, from Nassau County and Suffolk County.
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Common Questions
Hydraulic hose basics FAQ
A flexible tube built to carry oil at thousands of psi while bending repeatedly. It has three layers: a tube compatible with the fluid, steel wire reinforcement that holds the pressure, and a cover protecting the reinforcement. It is the only part of a hydraulic system asked to move, which is why it is the part that wears out.
A hose is the flexible tube on a reel, sold by the foot. An assembly is that hose cut to length with fittings crimped onto both ends at the correct orientation, tested and ready to fit. When a line fails, an assembly is what you actually need.
Braided hose has one or two layers of wire and flexes more readily, which suits circuits that move. Spiral hose has multiple layers wound in alternating directions, handling higher pressure and higher impulse cycling, but it is stiffer and needs a larger bend radius.
The specification printed along the outside of the hose, repeated every foot or so. It typically gives the standard such as SAE 100R2, the size, the working pressure and the manufacturer. If a hose carries no layline, nobody can verify what it is, which is a reason to replace it.
Working pressure is the maximum continuous operating pressure the hose is rated for, and it is the number to specify against. Burst pressure is where it fails on a test rig, typically around four times working. Burst is a manufacturing benchmark rather than a capability.
Because the cover protects the wire reinforcement that actually holds the pressure. Once the cover is through, that wire is exposed to moisture and starts corroding. The hose is on borrowed time even though nothing is leaking yet.
Never with your hand. At working pressure a pinhole produces a jet fine enough to be invisible and strong enough to go through skin, and the resulting injury is a surgical emergency. Use a piece of cardboard at arm's length, depressurise first, and remember circuits hold pressure after the engine stops.
The hose itself is not repaired, it is replaced. There is no acceptable splice or patch on a pressurised hydraulic line. What can often be reused is the fittings, which is why bringing the old assembly in is worthwhile even when the hose is destroyed.
Ask The Counter
Send us the layline
A clear photo of the printing along the hose tells us most of what we need. If it has worn off, a photo of both ends and the machine covers the rest.
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Assemblies built while you wait
1/8 inch to 2 inch, up to 6,000 psi. Two Long Island counters, six days a week.