Excavator Digging Beside the Scaffold

About this drawing

An excavator at work moves a lot like a human arm, with a shoulder, an elbow and a wrist. The trick behind it is hydraulics, which uses oil under pressure to push enormous loads with surprising precision.

Those shiny tubes running along the arm are hydraulic cylinders, each with a piston inside. When a pump forces oil into a cylinder, the piston slides out and pushes. When the oil flows back, the piston pulls in. Because oil barely squeezes, nearly all the force travels to the other end, letting a fairly modest engine lift tons of dirt.

The boom rises from the cab, the stick is the middle section and the bucket sits at the tip, with teeth that bite into the ground. The cab and engine ride on a turntable that can spin all the way around on top of the tracks, so the machine can dig in front and dump to the side without moving.

Operators run everything with two joysticks, one in each hand, and it takes lots of practice to blend the motions smoothly. Swap the bucket for a breaker, a grapple or an auger and the same machine takes on a whole new job, which is why excavators are among the most useful tools on any job site.

• excavator
• construction
• heavy equipment
• job site
• hydraulics