A coiled air hose gives an operator reach without leaving a hose on the floor. It also costs pressure, limits flow and has a working length considerably shorter than the figure on the label. For a hand tool at a bench it is the right answer. For a continuous-duty grinder it usually is not.
This guide covers how coiled hose is specified, the difference between stretched and working length, the pressure drop nobody accounts for, and where a straight hose on a reel does the job better.
What the length on the label means
Coiled hose is sold by stretched length: the length it reaches if pulled out straight. That is not the length you can use.
Three lengths matter:
- Stretched length. The catalogue figure.
- Working length. Typically 60 to 75 per cent of stretched, because pulling a coil to its full extent permanently deforms it and it never recovers its coil.
- Relaxed length. What it occupies when hanging, usually a small fraction of the total.
A 10 m coiled hose is a 6 to 7 m hose in practice. Specify on the distance the operator actually needs to cover, then choose a stretched length around 1.5 times that.
Pulling a coil to its full stretched length is the most common way coiled hoses are ruined. Once the coil has been pulled flat it drags on the floor, which is the problem the coil existed to solve.
Pressure drop: the number that decides whether the tool works
A coiled hose is longer than it looks and the coil itself adds resistance. The air travels the full stretched length regardless of how far the operator has walked, and every turn of the coil is a bend.
Two practical consequences:
Bore matters more than on a straight hose. A 6 mm bore coiled hose feeding an impact wrench will starve it. For anything with sustained consumption, step up: 8 mm, 10 mm or a straight hose.
Pressure at the tool is what counts. Measure it at the tool under load, not at the wall. A tool rated for 6.3 bar that sees 4.5 bar at the inlet is not going to deliver its rated torque, and the operator will compensate by leaning on it.
For continuous-duty tools, sanders, grinders, large impact wrenches, a coiled hose is usually the wrong choice. Use a straight hose on a retractable reel, which gives reach without the coil's resistance.
Material
Polyurethane is the default and the right choice for most workshop duty. It recovers its coil well, resists abrasion from being dragged across a bench edge, and stays flexible in the cold. Ether-based PU is the version to specify where the environment is damp, since polyester-based PU is vulnerable to hydrolysis.
Polyamide holds higher pressure and is stiffer. It makes a coil that springs back harder, which is useful where the hose must retract out of the way, and less comfortable to work against all day.
Rubber coiled hoses exist for heavy duty and hot environments, and they are heavy. The weight is what the operator feels.
Ends, and the fitting that breaks first
The junction between the coil and the fitting is where coiled hoses fail, because that is where the bending is concentrated every time the hose is pulled.
Two features are worth paying for:
- Strain relief at both ends, a moulded or fitted sleeve that spreads the bend over a longer length instead of letting it happen at the ferrule.
- A swivel on the tool end. Without it, the operator turns the tool and the hose winds up, and the coil fights back. A swivel removes the wind-up and takes torsional load off the fitting.
Specify the coupling profile at the same time, and to the plant standard. A coiled hose with the wrong plug is a coiled hose nobody uses.
Where a coiled hose belongs
Good fit
- Bench work with a short-duty tool: blow gun, small impact wrench, screwdriver, stapler.
- Assembly stations where a hose on the floor is a trip hazard.
- Overhead drops where the coil holds the hose up out of the working area.
- Vehicle and machine service bays with a defined working radius.
Poor fit
- Continuous-duty tools with high air consumption.
- Runs where the operator needs more than a few metres.
- Environments with sharp edges or hot surfaces the coil will catch on.
- Anywhere the hose will be pulled to full stretch routinely.
Safety
The same rules apply as for any compressed-air hose, and two are specific to the coil.
Use a safety coupling. Releasing a pressurised hose whips it, and a coiled hose carries stored energy in the coil as well. A safety coupling vents downstream pressure before the plug releases.
Watch the recoil. A coil that is released under tension snaps back. That is the point of the coil, and it is also a hazard at head height. Mount the anchor point so the recoil path is clear of people.
Inspect the ends. A coiled hose that has been pulled to full stretch repeatedly will show it first at the strain relief, and the failure when it comes is at pressure.
A specification checklist
- Working distance required, then stretched length at roughly 1.5 times that.
- Bore, sized on the tool's air consumption and the full stretched length, not the distance walked.
- Material: PU for general workshop use, ether-based where damp, PA where a firmer return is wanted.
- Working pressure at temperature, since plastics derate as they warm.
- Strain relief at both ends, and a swivel on the tool end.
- Coupling profile to the plant standard, safety type.
- Anchor point positioned so the recoil path is clear.
- An honest check: would a straight hose on a reel serve this station better?