A pneumatic hammer is a piston that air drives forward to strike and back to reset, and its energy per blow is gauge pressure times bore area times stroke: a 30 mm bore with a 50 mm stroke at 6 bar gauge gives at most 21.2 J. Each blow also uses about 0.25 L of free air, so 10 blows a second takes 148 L/min and the compressor, not the hammer, sets the rate.
Part of Pneumatic Systems
The pneumatic hammer replaces the swing of a hand hammer with a rapid train of small blows from a piston driven by compressed air, used for riveting, chiselling, scaling and light forging.
Energy Per Blow Is Force Times Stroke
The air pushes on the piston area through the whole stroke.
Worked example (the carrier’s hammer): 30 mm bore, 50 mm stroke, 0.5 kg piston, 6 bar gauge.
- Bore area = π / 4 x 0.03² = 7.069 x 10⁻⁴ m²
- Force = 600,000 Pa x 7.069 x 10⁻⁴ m² = 424 N
- Energy = 424 N x 0.05 m = 21.2 J, matching the carrier’s “about 20 J”
This is the most the air can supply, assuming full pressure all the way along the stroke and no back-pressure on the other side of the piston. Real blows are weaker. For comparison the carrier says it is about a hand-hammer swing, but at many blows a second.
The Hammer Eats Air
Each forward stroke fills the swept volume with air at 7 bar absolute.
- Swept volume = 7.069 x 10⁻⁴ x 0.05 = 3.534 x 10⁻⁵ m³ (0.0353 L)
- Free air used = 0.0353 L x 7 = 0.247 L, about 0.25 L, per blow, ignoring the return stroke
- At 10 blows per second = 2.47 L/s = 148 L/min
- The carrier’s reference compressor delivers 235.6 L/min before losses (Piston Compressor), which supports at most 235.6 / 60 / 0.247 = 15.9 blows a second on the forward stroke alone
So the carrier’s “10-50 blows per second” is a range of valve speeds, not of what one compressor can sustain; a 50 blows-per-second hammer of this size would need over 700 L/min. The rate is limited by the air, not by the mechanism. A big receiver lets a small compressor serve short bursts.
How It Works and What You Need
- Air enters behind the piston, driving it forward to strike.
- A valve (a spool or rotary valve) switches the air to the front, retracting the piston.
- The cycle repeats.
You need a steel cylinder bored and honed true, a hardened piston, a spool or rotary valve, a tool holder with a retainer that keeps the chisel in the tool, and handles. Use the air-motor and hose practice in Pneumatic Tools and Devices.
Common Mistakes
- Firing the hammer with nothing under the chisel. All the energy goes into the tool or the tool holder, and the chisel can fly out. Use a retainer and only fire against a workpiece.
- Expecting full energy at a long hose. Pressure drops in a hose and the hammer loses blow strength; see Pipe Sizing.
- A tool that does not match the work. For forging, see Forging for the material side.
Safety
A hammer fired loose throws its tool
A pneumatic hammer fired without a workpiece, or with a chisel not held by a retainer, can throw the chisel or rivet set out of the holder as a projectile. Always fit the retainer, fire only with the tool against the work, and keep other people out of the line. Wear eye protection, ear protection and gloves, since the blows are loud and the handle transmits vibration. Shut the supply and bleed the hose before changing tools.
What’s Next
- Learn next: Air Drill and Grinder — a rotary air tool
- Combine with: Air Storage and Treatment — a receiver for bursts