Excavators are heavy construction equipment consisting of a boom

Backhoe

A backhoe, also called a rear actor or back actor, is a piece of excavating equipment or digger consisting of a digging bucket on the end of a two-part articulated arm. They are typically mounted on the back of a tractor or front loader...

, stick, bucket

Bucket (machine part)

A bucket is a specialized container attached to a machine, as compared to a bucket adapted to the form of a human being...

 and cab on a rotating platform (known as the "house"). The house sits atop an undercarriage with tracks

Caterpillar track

Continuous tracks or caterpillar tracks are a system of vehicle propulsion in which modular metal plates linked into a continuous band are driven by two or more wheels...

 or wheel

Wheel

A wheel is a device that allows heavy objects to be moved easily through rotating on an axle through its center, facilitating movement or transportation while supporting a load, or performing labor in machines. Common examples found in transport applications. A wheel, together with an axle,...

s. A cable-operated excavator uses winches and steel ropes to accomplish the movements. They are a natural progression from the steam shovel

Steam shovel

A steam shovel is a large steam-powered excavating machine designed for lifting and moving material such as rock and soil. It is the earliest type of power shovel or excavator. They played a major role in public works in the 19th and early 20th century, being key to the construction of railroads...

s and often called power shovels. All movement and functions of a hydraulic excavator are accomplished through the use of hydraulic fluid

Hydraulic fluid

Hydraulic fluids, also called hydraulic liquids, are the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water...

, with hydraulic cylinder

Hydraulic cylinder

A Hydraulic cylinder is a mechanical actuator that is used to give a unidirectional force through a unidirectional stroke. It has many applications, notably in engineering vehicles.- Operation :...

s and hydraulic motor

Hydraulic motor

A hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and angular displacement . The hydraulic motor is the rotary counterpart of the hydraulic cylinder....

s.