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Jackhammer pneumatic drill by John Curtis, US Navy

Jackhammers (pneumatic drills)

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by Chris Woodford. Last updated: April 25, 2017.

Twenty thousand years ago, if you'd needed to dig a hole in rough ground, chances are you would have found yourself swinging a sharpened deer antler over your head. Modern pickaxes are based on pretty much the same idea. The long wooden handle and metal blade act like levers to magnify the force you generate with your back muscles and arms. It's simple technology, but it's very effective.

Today, if you want to dig a hole in a hurry and there's a thick lump of concrete or asphalt in your way, you're most likely to use a jackhammer, also known as a pneumatic (air-powered) drill, rock drill, or pavement breaker. A strong and skilled road worker can swing a pickaxe 10 times a minute or more, but a jackhammer can pound the ground 150 times faster—that's 1500 times a minute! Pretty amazing, but how exactly does it work?

Photo: A typical pneumatic jackhammer drill being used in a road repair project. Picture by John P. Curtis courtesy of US Navy.

Pneumatics is the power of compressed air

Naval rescue worker attacks a concrete structure with a jackhammer pneumatic drill.

Photo: Jackhammers aren't just used for construction: since they offer the fastest way of breaking through concrete and stone, they're often vital tools in emergency rescue work. Here, a worker from the US Naval Air Station Sigonella Fire and Rescue Team is using a pneumatic jack hammer to smash through concrete during a training exercise. Picture by Gary A. Prill courtesy of US Navy.

You've probably never handled a jackhammer, but you use exactly the same technology every time you ride on a bicycle or travel by car. The rubber tires that carry you smoothly down the road are inflated with air, so the force of your weight pushing down is exactly balanced by the pressure of the air pushing you upward. Tires are an example of pneumatic technology, which means they use the force of air pressure. (You may have heard of a similar technology called hydraulics that uses the force of liquid pressure.)

You can't see air, but it's a surprising thing. It's a mixture of gases, mostly nitrogen and oxygen, with its molecules constantly zooming back and forth like angry bees. When air is trapped in a container, such as a bicycle tire, molecules of gas are repeatedly crashing into the rubber walls and bouncing back again. Each time one of these collisions happens, the molecules give a tiny push to the rubber. With millions of collisions happening all the time, the air exerts quite a pressure (defined as the force acting per unit of area) on the rubber—and that's what keeps the tire inflated. (The hotter the air is, the faster the gas molecules move, the more energetically they collide, and the more pressure they exert. That's why tires inflate more on hot days and after a long car journey.)

You might have seen pneumatics in action elsewhere. Blowpipes are another good example. When those angry savages from your comic books blow poisoned darts at their enemies, they're using air pressure to force a missile down a tube at high speed. In olden days, big department stores used pneumatic transport tubes to send money or messages rapidly from one floor to another.

Steam engines use pneumatics too; instead of air, they use high-temperature, high-pressure water vapor (steam) to push pistons back and forth and turn wheels at high speed. Vacuum cleaners, which use suction to remove dirt from soft furnishings, use the same principle in reverse—sucking air in rather than blowing it out.

Jackhammer being used on road, linked to compressor by air hose

Photo: A construction worker using a pneumatic drill. Note the red compressed air hose coming out of the left-hand side of the drill, which is supplied by the large green portable air compressor (marked Sullair), hooked up to the pickup truck on the left of the photo. Picture by Renae Kleckner courtesy of US Air Force.

Inside a jackhammer

Simple animation showing how a jackhammer

Artwork: This little animation shows what happens inside a drill. Note how the blue valve at the top flips back and forth so the air changes direction. This makes the orange piledriver pound up and down, bashing the gray drill bit repeatedly into the ground. Note that this is a considerable simplification of what happens in a real drill, where the arrangement of valves, air passages, and so on is much more complex. You can get a sense of how much more complex real drills are from the illustration of Charles Brady King's original drill design, below.

Back to jackhammers. The first time you saw someone digging a hole in the road with a tool like this, you probably thought the equipment was electric or powered by a diesel engine, right? In fact, the only energy involved in making a jackhammer pound up and down is supplied from an air hose. The hose, which has to be made of especially thick plastic, carries high-pressure air (typically 10 times higher pressure than the air around us) from a separate air-compressor unit powered by a diesel engine.

The air compressor is a bit like a giant bicycle pump that never stops blowing air. When the worker presses down on the handle, air pumps from the compressor into the jackhammer through a valve on one side. Inside the hammer, there's a circuit of air tubes, a heavy piledriver, and a drill bit at the bottom. First, the high-pressure air flows one way round the circuit, forcing the piledriver down so it pounds into the drill bit, smashing it into the ground. A valve inside the tube network then flips over, causing the air to circulate in the opposite direction. Now the piledriver moves back upward, so the drill bit relaxes from the ground. A short time later, the valve flips over again and the whole process repeats. The upshot is that the piledriver smashes down on the drill bit over 25 times each second, so the drill pounds up and down in the ground around 1500 times a minute.

Jackhammers, and the air compressors that power them, come in all different shapes and sizes. The drill bits on the end are interchangeable too. There are wide chisels, narrow chisels, and tools called moil points for fine work. A skilled drill operator can loosen chunks of road in just 10-20 seconds, making light work of what our ancestors—with their antler picks—would have found truly backbreaking work!

Who invented the jackhammer?

An illustration from Charles Brady King's jackhammer patent from 1892/1894.

Artwork: Charles Brady King's jackhammer. Artwork courtesy of US Patent and Trademark Office.

Although there are hundreds of patents for jackhammers and pneumatic tools, the earliest appears to have been filed by Charles Brady King on May 19, 1892 and granted on January 30, 1894.

King's design is a more elaborate version of the one I've sketched out in my animation up above, but essentially works the same way with a reciprocating (back-and-forth) valve making air move first one way and then another, moving a piston up and down, and bashing a drill bit repeatedly into the ground. I've colored the valve in blue and, in this design, it shifts from side to side, changing the way air flows between the inlet ports (colored yellow) and outlet ports (colored brown).

How does it work? When the valve is in the position shown here, air enters through the thick yellow hose at the top and follows the thinner paths shown in yellow, pushing the piston (red) downward and smashing the hammer (green and gray) into the ground.

As the piston moves down, air flows back up through one of the pipes and pushes the blue valve over to the right, so the air now follows the brown paths and exits.

Here's a small selection of three early jackhammers on record at the US Patent and Trademark Office, including King's. You can find many more examples if you search for "pneumatic drill" or "jackhammer" at the USPTO website:

Other kinds of jackhammers

Not all jackhammers use compressed air, so it's a bit misleading to refer to them all, generically, as "pneumatic drills." Some are driven by powerful electric motors, which rotate a crank or cam that converts the motor's spinning (rotary) motion into back-and-forth (reciprocating) motion, pumping a piston, forcing a small air cushion back and forth, so powering a second piston connected to a shaft that repeatedly hammers the drill or other tool. Electric jackhammers have the big advantage that you can operate them without a separate air compressor unit (you can use them wherever there's an electric power supply), though they sometimes struggle to cut through the thickest rock.

Other jackhammers are operated hydraulically so, instead of using compressed air, they're powered by a continuous stream of hydraulic fluid (perhaps oil or water with additives). This flows through a hydraulic motor or turbine, powering a crankshaft and piston that hammers the drill bit. Hydraulic jackhammers are often used for underground mining where pneumatic tools are less suitable. Sometimes the hydraulic fluid that powers the drill is also used as a "cutting fluid" (for cooling and lubrication).

Because pneumatic jackhammers are incredibly noisy, engineers are constantly trying to develop quieter ways of achieving the same end. Perhaps surprisingly, much of the noise that a jackhammer makes comes not from the shattering pavement but from its own internal mechanism—the piledriver banging against the drill bit—so making a quieter machine means designing a hammer that works in a different way. In 2000, Brookhaven National Laboratory produced a helium-powered hammer called RAPTOR that worked like a high-speed rifle, firing tiny steel nails into rock to break it apart. The idea hasn't caught on yet. Instead, electric jackhammers seem to be growing in popularity, largely because they're much quieter than traditional pneumatic ones.

Simplified hydraulic jackhammer mechanism from US Patent 5,117,923 by Wolfgang Wuhrer, Sulzer Brothers Limited.

Artwork: One example of how a hydraulic jackhammer can work. Hydraulic fluid (turquoise, 24) flows in through a nozzle at top left, making a turbine (red, 25) rotate. This spins a transmission (dark green, 7), that powers a crank and connecting rod (dark blue, 12, 6). These move a sliding guide (yellow, 14a) back and forth, allowing a heavy mass (blue, 2a) to strike a rod (green, 15) attached to the tool bit. There's also an ingenious second part to this mechanism. The transmission simultaneously rotates the driveshaft (gray, 13), turning the drill chuck (gray, 16) and making the bit rotate. From US Patent 5,117,923: Hydraulic jackhammer by Wolfgang Wuhrer,Sulzer Brothers Limited, June 2, 1992, courtesy of US Patent and Trademark Office.

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A yellow jackhammer mounted on an excavator, breaking up rubble.

Photo: Right: A jackhammer mounted on the end of an excavator. Picture by Matt Coleman-Foster courtesy of US Air Force.

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