Compressed air can run hammers, drills, grinders, spray guns and clamps, and it suits them because air tools are light, fast and cannot electrocute you, but they are hungry: a vane motor delivering 300 W from air at 6 bar gauge needs at least 68 L/min of free air, and a few tools running together can use up a small compressor’s whole output. Compressed air must never be pointed at people or used to blow dust off clothing or a bench.
Part of Pneumatic Systems
A pneumatic tool turns the energy in compressed air into hammering, rotation or spraying. Each tool is a piston, a vane motor or a nozzle on the end of a hose.
One Compressor Feeds Many Kinds of Tool
- Hammer and chisel: a piston driven back and forth by air; see Pneumatic Hammer.
- Drill and grinder: a vane motor; see Air Drill and Grinder.
- Spray gun: a nozzle that atomises liquid; see Spray Equipment.
- Clamps and presses: a small cylinder with a valve. Air clamps are fast but spring; a clamp that must hold precisely needs a lock.
- Blow-forming: air to inflate hot glass or plastic in a mould; see Blow Molding Basics.
Air tools do not carry an electric motor, so there is nothing to short out in wet conditions. The carrier article adds that air motors slow under load without overheating.
Air Tools Need More Air Than Beginners Expect
A tool cannot give out more work than the air brings in. Expanding 1 m³ of free air from 6 bar gauge (7 bar absolute) down to atmospheric pressure can do at most 3.5 x 101,325 x (7^0.2857 - 1) = 3.5 x 101,325 x 0.744 = 263,700 J, using the adiabatic expansion formula from Gas Laws in Practice.
Worked example: a 300 W tool.
- Free air per second at best = 300 W / 263,700 J/m³ = 0.00114 m³/s
- In litres per minute = 0.00114 x 60,000 = 68 L/min
That is the least; a real vane motor does not expand the air fully, so it uses more. A piston compressor of the carrier’s reference size delivers 235.6 L/min before losses (Piston Compressor), so a few such tools exhaust it. Size the compressor to the tools, not the tools to the compressor.
Common Mistakes
- Choosing a tool first and the compressor second. Add up the air demand of the tools that run at once.
- Running a tool at higher pressure than it is made for. Tools, grinding wheels and hoses are rated; more pressure means more speed and more stress.
- Using a tool as a toy or a duster. A nozzle is a jet, not a brush.
Safety
Compressed air is not a cleaning tool and not a toy
A jet of compressed air aimed at skin can force air through the skin or a wound into the tissue, and air that reaches a vein can cause an air embolism, which can be fatal. A jet aimed at an ear, an eye, the mouth or any body opening can damage it. Blowing air over clothes or a bench drives swarf, dust and splinters into eyes and skin, and fans loose dust into the air. Never point an air nozzle at a person, never use air to dust off clothing or hands, and sweep or brush a bench instead. Wear eye protection whenever air tools run, and ear protection for hammers.
A hose or coupler can whip
A hose that comes off a coupler under pressure thrashes violently. Bleed the line before disconnecting, secure hoses, and see Quick-Connect Couplers.
What’s Next
- Learn next: Pneumatic Hammer — the simplest air tool
- Combine with: Piping and Fittings — getting air to the tools