One of the newest nail gun machines to hit the market is the combustion nailer. These portable guns generate hammering power with internal combustion, the same force that keeps your car going (see How Car Engines Work).
At the most basic level, combustion guns are a lot like pneumatic nailers. They have a long blade attached to a sliding piston, which is moved by an imbalance in atmospheric pressure. The piston moves downward when there is greater pressure above it, and it moves upward when there is greater pressure below it.
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The difference between pneumatics and combustion models is the source of the pressure imbalance. Just like your car, combustion guns have a reservoir filled with a flammable gas. An electronic control mechanism releases a little of this gas into a combustion chamber just above the piston head. A small fan in the combustion chamber vaporizes the gas, mixing it up with the air particles.
This design has a double trigger mechanism. To hammer a nail, you need to pull down the trigger and press the barrel up against the surface at the same time. Pressing the barrel down pushes back a metal valve around the main cylinder. This controls the gas intake and exhaust cycle of the gun.
Here's what happens when you activate both triggers:
- The valve piece (shown in green) slides back around the cylinder. As it moves back, the valve closes the exhaust port at the top of the gun. As it keeps moving back, it briefly opens the intake port from the gas supply (shown in blue), and then closes it again. This lets a small amount of gas inside, which the fan mixes with the air.
- The gun's battery sends a charge to a spark plug at the top of the combustion chamber. This ignites the gas, causing a small explosion.
- The pressure of the explosion propels the piston downward, driving the blade into the nail so that the nail is shot from the gun. As the piston pushes downward, it compresses the air in the cylinder.
- When you lift the gun off the nailing surface, the valve slides back down. This opens the exhaust port, so the exhaust can escape.
- The compressed air in the return chamber pushes the piston back up, to the "ready" position. Essentially, the air in the return chamber acts like a spring.
The second trigger in this gun is intended as a safety device: you have to pull the trigger and press the gun against a surface to shoot a nail. As we'll see in the next section, this mechanism helps prevent some nail gun injuries, but it may lead to other sorts of accidents.