What are the parts of an excavator?

We can all picture the shape of an excavator, but what are the parts of an excavator called and what functions do they perform? While excavator design continues to evolve and improve, the basic form has remained consistent for decades. Obviously, different models from different manufacturers will have individual excavator parts and functions not common to all types. However, they all consist of the same three sections and basic components which we will discuss here.

The three main sections of an excavator are the undercarriage, the house and the arm. The undercarriage is the lowest section responsible for moving the excavator around the work area. The house sits above this and contains the power source and operator controls. Finally, the arm projects from the main body of the excavator and is responsible for performing most actual physical work.


1. Tracks

Traditionally excavators have been equipped with metal caterpillar tracks made of a series of steel plates connected by steel pins. These form what is known as a continuous track, running on rollers and driven by two toothed wheels known as track sprockets. Steel was initially used as it is extremely hard wearing. These can damage paved surfaces so are sometimes equipped with rubber pads. Modern excavators can be fitted with rubber tracks reinforced with steel wire or even wheels to minimise this still further.

2. Track Frame

This is the main body of the undercarriage, a solid rectangular steel frame with the track bodies on its sides. It is connected to the House above by a centre pin. The slew ring, swing gear and swing bearing are located here and a hydraulic swivel at the apex allows 360 degree rotation. This is responsible for left to right movement of the body when the excavator is stationary.

3. Final Drives

These consist of a hydraulic motor and a gearing system connected by a drive shaft to the engine above. This provides power to the tracks and allows each track to be powered individually for left and right turning. Stopping one track while the other moves allows the whole excavator to turn on the spot.

4. Blade

This is not included on all models or may be an optional attachment. The addition of a dozer blade to the undercarriage allows the excavator to move loose material for ground clearance.


1. Operator Cab

This is an enclosed cabin housing all the excavator controls and seating for the operator. This provides protection from the elements and falling materials while all round glazing offers 360 degree visibility.

2. Counterweight

As a fully extended digging arm is likely to tip an excavator, a large counterweight is incorporated into all designs. This is incorporated into the upper housing towards the rear of the excavator. Until the 1990s, these always projected beyond the rear of the tracks for maximum stability. In 1993 the first zero tail swing excavator was produced, allowing greater manoeuvrability in confined work spaces.

3. Engine

Excavators derive their power from diesel engines as it produces a higher horsepower than petrol. As noted earlier, the engine produces power for the tracks to move the excavator around the worksite. It also powers three hydraulic pumps, two of which supply pressurised oil to the arms, accessories and swing motor. The third, lower pressure pump reduces physical effort operating controls by pilot control of the spool valves.

4. Fuel and Hydraulic Fluid Tanks

These are both located in the rear housing close to the engine, giving protection and allowing easy access for refuelling.


The easiest way to visualise the operation of an excavator digging arm is to imagine a human arm. With the arm extended at the shoulder with the elbow bent and a cupped hand, it forms the same shape. During operation, the hydraulics act in much the same way as the muscles of the arm in moving the different components.

1. Boom

The boom forms the upper part of the digging arm, attached to the front of the house and governing up and down movement. In mono booms, one or two boom cylinders at the base lift the boom up and only vertical movement is possible. Less common are knuckle booms which can move left and right and some compact excavators have booms that can pivot 180 degrees horizontally.

2. Stick

Also known as a dipper arm, the stick is attached by a hinged joint to the end of the boom. A hydraulic cylinder known as the stick, arm, and crowd or dipper cylinder extends from the top of the boom to the end of the stick. When operated, this pulls the stick toward the boom, dragging the bucket through the ground as the boom moves down. This provides the digging movement for the excavator.

3. Bucket

This is located at the bottom end of the stick, attached by another hinged joint. The bucket cylinder on the outside of the stick can pull the bucket inwards to lift dug material. Once the arm is lifted, this cylinder can then extend to tip the bucket, releasing the held material. Buckets come in a variety of shapes and sizes to hold different volumes of waste or cut through different materials.

4. Attachments

These are optional tools that can be attached to the excavator in place of a bucket to increase its range of functions. These include augers, log splitters, earth drills, compactors and many more. For a company or individual already possessing an excavator, attachment hire can vastly increase the variety of jobs it can perform beyond basic digging and clearance. Many models of excavator have some form of quick coupler allowing attachments to be quickly fitted and removed.

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