How Does an Excavator Work?by Steve Smith; Updated April 24, 2017
Power and Drive
An excavator runs on diesel power because it produces a higher horsepower and is more robust for heavy duty labor. The engine powers the tracks which are similar to tank tracks, and the hydraulic motors which raises and extends the excavator arm. All power is supplied by the diesel engine, and the controls for movement in forward and reverse are operated from the control cabin. An operator will use pedals and levers to move the machine forward and backward, and to steer the vehicle.
The arm of the excavator is attached to the lower part of the frame chassis. This arm has three hydraulic pistons with chromed steel piston arms. The arm has two main sections and a bucket loader. The two main sections are jointed with a hinge. One piston is attached to the underneath side of the first section and one on the top side of the second section. When the first piston extends, the rod pushes against the arm and raises it, extending the section. The second arm contracts or expands, raising and lowering the second section for more reach. An additional hydraulic piston moves the bucket loader forward and backward so the arm can scoop and dig.
The tracks are rigid and fixed in place. They are stationed around a series of gears that turn by power received from the drive shaft, connected to the engine. When in gear, the tracks roll the machine forward or backward in a straight line. To turn the machine, one track is stopped completely, and the other is put in motion, either in forward or reverse. This causes the machine to turn in an arc. An operator can also put one track into reverse and another into forward to spin the machine in a tighter circle. This requires two separate drive systems, and a more complicated transmission. It is not available on all vehicles. In addition, some excavators have a pivoting cab that can swivel 360 degrees. This is powered by another hydraulic motor that receives drive from the main engine.