Before working with excavators, you need to know how they work. Excavators are essential heavy construction machines designed for digging, moving and lifting materials. They help make construction and excavation projects safer and more efficient. Understanding what the basic parts of an excavator are can help you be a better operator. Learn the excavator’s components and functions in this guide.
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Knowing the basic parts of an excavator and how they work can help you choose, work with and maintain your machine. You’ll know what each part is, what it does and how everything fits together. Here are the main excavator components:
The boom is a fundamental component of an excavator. This large main part extends outward from the machine’s body. It primarily provides the excavator with its reach, allowing the operator to position the arm and bucket precisely for digging, lifting or placing materials. Booms come in various lengths and configurations, depending on the excavator’s intended application. Long booms are generally used for tasks requiring an extended reach, while shorter booms are better for confined spaces.
The arm, also called the stick, connects the boom to the bucket and helps control the excavation’s depth and precision. By extending and retracting the arm, the operator can adjust the distance between the boom and bucket, enabling precise digging, grading and lifting. The arm’s length varies depending on the excavator’s size. While mini excavators have shorter arms for better maneuverability in tight spaces, larger excavators have longer sticks, allowing for deep excavations.
The bucket is the attachment at the end of the arm responsible for digging, scooping and carrying materials. Buckets come in various shapes and sizes, each designed for specific tasks. Excavator buckets typically have teeth or cutting edges for breaking through tough soil or rock. They can be swapped out for other attachments, like grapples or thumbs, to expand the excavator’s capabilities. The bucket’s size and shape significantly affect productivity and efficiency, so choosing the right one for the application is important.
The cab is the operator’s compartment. It contains the operator’s seat and the control panel. From here, the operator manages the machine’s functions, using various controls, joysticks and pedals to operate the boom, arm, bucket and other movements like rotation and travel. Modern excavator cabs are equipped with air conditioning, ergonomic seating and advanced technology, enhancing operator safety, comfort and productivity.
The excavator’s undercarriage supports the machine’s weight, provides stability and facilitates movement. It includes tracks or wheels, depending on the excavator type. Tracks offer excellent traction and weight distribution, enabling crawler excavators to navigate rough and uneven terrains more easily. Wheeled excavators provide maximum agility on smoother surfaces such as asphalt and allow more mobility. The undercarriage may have features like adjustable width or retractable tracks to adapt to various job site conditions, ensuring the excavator’s stability and maneuverability.
Excavator engines usually run on diesel fuel. The engine’s size and power output depend on how big the excavator is and how it’s used. Modern engines are designed for improved efficiency and reduced emissions to meet strict environmental standards. Engines power the excavator’s movements and supply the energy needed to operate the hydraulic system.
The excavator’s hydraulic system is a complex network of high-pressure hoses, pumps, valves and cylinders that control the movements of the boom, arm and bucket. Using the hydraulic system, the operator manipulates these components to complete tasks. The hydraulic system is exceptionally responsive and powerful, making it an essential part of the excavator. It provides the strength needed to carry out heavy-duty tasks while maintaining accuracy and control in the operator’s hands.
The counterweight is a heavy component, often located at the excavator’s rear. It provides balance and stability during lifting and digging operations. Since the excavator’s bucket at the front is frequently loaded with materials in the bucket, the counterweight opposes the weight of these materials to prevent the excavator from tipping over. Counterweights are adjustable and can be tailored to the machine’s specific requirements, ensuring safe operation and preventing accidents.
Swing gear, typically loaded at the machine’s base, allows the excavator to perform a 360-degree rotation. This feature is essential for positioning the bucket accurately and efficiently without needing to reposition the entire machine. The operator can easily swing the excavator to reach different work site areas. It greatly enhances productivity and versatility, as the excavator can work within a wider radius without physically moving the undercarriage.
Some excavators are equipped with an optional blade at the front end for leveling and grading tasks. The operator can adjust this blade to control the grading depth and angle, making it a critical feature for projects requiring precise earthwork and leveling. The blade complements the excavator’s digging and material-handling capabilities, transforming it into a versatile machine for site preparation and finish grading work.
Here are the answers to some common excavator questions to help you learn more about these machines and how to keep them in good condition.
Excavators use a combination of the boom, stick, bucket and hydraulic system to dig, scoop and lift materials. The operator controls these functions from the cab. The hydraulic system activates these components, allowing the excavator to dig into the earth, scoop materials, and perform precision tasks like trenching or loading trucks.
Excavators come in different types to suit diverse needs. Standard crawler excavators are versatile and excel at many tasks. Mini excavators are compact and ideal for tight spaces, while wheeled excavators offer mobility on the road. Long-reach excavators extend for specialized reach and depth requirements. Your choice of excavator depends on the specific job and its demands.
Excavators find extensive use across construction and excavation projects. They’re essential for digging trenches, excavating building foundations, leveling and grading land, demolishing structures, and loading or unloading heavy materials. Their adaptability and precise control make them indispensable on job sites.
The boom and arm, undercarriage and cab are the 3 major parts of an excavator.
With a legacy of excellence, Cat® excavators are renowned for their reliability, power and innovation. Whether you need a compact mini excavator or a heavy-duty crawler, we have the solution. Gregory Poole is your trusted partner in acquiring and maintaining Cat excavators. Our experts are ready to assist you in selecting the right equipment for your needs and provide top-notch service and support throughout your ownership. Explore our range of equipment today and elevate your construction and excavation projects with the best in the industry. Reach out if you have any questions.
With an expert excavator operator behind the controls, the fluid, fast, and precise movements of the excavator arm can be so perfectly performed and timed one might think the operator has simply grown a new arm themselves. But anyone who’s sat behind the controls knows it takes knowledge of how the machine works and skill in timing to efficiently control the arm.
To take a better look at how the arm works, how it's controlled, and how each part comes together to pull off its work, read on for a short exploration of how exactly an excavator arm performs its duties.
All the main parts of an excavator arm work together to create a perfect, fluid movement — a feat that combines smart engineering and operator skill. » Click video to play/pause animation.
An excavator arm consists primarily of a boom, stick, and attachment. A bucket is the most common attachment. Hydraulic cylinders are connected to segments of the arm and from the cab the operator extends and contracts the cylinders. This extending and contracting pivots parts of the arm at connection points to raise and lower the arm, extend it, or curl and uncurl the attachment (or bucket).
Sometimes only one cylinder or set of cylinders will be put to use to control the arm, but most commonly the operator will engage multiple cylinders simultaneously to perform more complex movements. By engaging the cylinders at different times and at different levels of force, the arm can be used to create fluid and precise movements.
For example, when trenching, the operator will contract the boom cylinders to lower the boom, extend the stick cylinder to extend the stick, and contract the bucket cylinder to uncurl the bucket with each cylinder working simultaneously to specific degrees. When the bucket contacts the ground, the operator will begin reversing the direction of each cylinder to create a scooping movement with the bucket.
By combining the movements of the arm with the pivoting ability of the excavator's upper house, the hydraulic cylinders on the arm allow the operator to dig to exact measurements, precisely place materials, spread materials, or even load waiting equipment.
An inside look at an excavator cab shows the joysticks and pedals the operator uses to operate the arm and transport the machine.Controlling an excavator arm is done though skillfully extending and contracting the cylinders at exact times and in exact orders. Inside the cab of an excavator, an operator will have a combination of joysticks at their sides, hand controls in front of them, and pedals on the floor. The arm is controlled by the joysticks while traveling can be done either through hand controls or by using the pedals. Using the joysticks, an operator will extend and contract the boom and stick and curl and uncurl the bucket, but also swing the entire house and arm in an infinite circle to position the arm.
Each joystick is sensitive to the amount of pressure applied to it and the cylinder will respond in kind to the amount of pressure by matching it with the speed at which it extends or contracts. This allows the operator to finely control how much movement each part is performing at specific times.
How the movements of each joystick control the action of the arms is determined by the control patterns assigned to the joysticks. In an excavator there are two common control patterns: ISO controls and SEA controls. In the most common pattern, ISO controls, the right joystick controls the movement of the boom and the bucket while the left joystick controls the movement of the stick and the swinging of the entire house and arm.
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A parts diagram shows each part and how they connect to perform the complete duties of the excavator arm.An excavator arm consists primarily of a boom, stick, and attachments. Hydraulic cylinders power the movements of the parts, pins bind parts together, and linkage attaches parts to one another in ways that allow for parts to pivot to perform actions. While not part of the arm, the entire hydraulic system is controlled by the main hydraulic pump and main hydraulic valve, located in the house of the machine, and connected to hydraulic cylinders through hydraulic lines throughout the arm and the entire machine.
The excavator’s boom is the largest of the main components of the arm. It is pinned directly to the house and pivots at that connection. This pivoting action allows the arm to rise and lower relative to the digging surface and also extend the reach of the arm or draw closer as it pivots.
View Excavator Booms
The excavator’s stick sits between the boom and the attachment and pivots at the connection to the boom. This pivoting action further allows the arm to position the attachment further or closer to the machine, as well as control the height of the bucket relative to the digging surface. By changing the angle of the stick the operator can position the bucket deeper than the tracks of the machine to dig or at a point high off the ground to load a machine or pile materials.
View Excavator Sticks
The attachment on an excavator is the tool at the far end of the arm. Increasingly, a wide range of attachments are used with excavators from attachments for clearing ground to attachments for hammering and breaking large rocks. The most common attachment is the bucket, but even excavator buckets can be as diverse as the materials they handle from teeth and side cutters for digging to thumbs to grab materials.
View Excavator Buckets
Most commonly, two cylinders on each side of the machine will be attached at one end to the house and at the other to the boom. Extending and contracting the cylinders will rise and lower the boom and subsequently the entire arm.
View Boom Cylinders
A stick cylinder attached to the boom and the stick and mounted at the top of the boom will rotate the stick as it pivots around its connection to the boom.
View Stick Cylinders
Unlike the other cylinders on the excavator arm, the bucket cylinder is connected to the bucket through linkage. By extending the bucket cylinder, the attachment will perform specific actions. In the case of a bucket, the bucket cylinder will control the loading and dumping of the bucket. Since the angle of the bucket can also be changed as the stick and boom are moved, holding a load with efficiency can require changing the angle of the bucket even after a digging motion has been completed.
View Bucket Cylinders
The linkage on an excavator arm are heavy-duty connectors that help define and control the movements of the attachments. These parts link together the stick and attachment while also allowing the attachment to move in very specific ways.
View Linkage
Increasingly, excavators on a worksite are viewed as tool handlers capable of taking on a wide range of roles beyond simple digging from leveling ground to boring post holes and more.
Some common excavator attachments are:
Instead of a standard attachment, a quick coupler is actually a connection point at the end of the arm that allows for the fast changing of other attachments. Buckets for specific jobs, forks for lifting, or other work-specific attachments can be swapped in minutes using a quick coupler.
Like a quick coupler, a tiltrotator isn’t a standard attachment, instead a tiltrotator extends the functionality of an excavator by introducing an additional point of control for the operator. Like a hydraulic wrist at the end of the arm, the tiltrotator allows the attachment to rotate and tilt without needing the machine to move. Digging a trench perpendicular to the cab with a bucket or delicately placing materials in exact positions with a grapple are new possibilities offered by a tiltrotator.
A thumb on an excavator works with a bucket to provide a grappling device opposite the bucket to capture and better secure the object the bucket is lifting. Large stones, logs, or other oddly shaped materials can be held by the bucket and thumb as they are moved by the arm.
Hammers mounted to the end of an excavator arm transform an excavator into mobile rock breakers. Large rocks and boulders can be attacked from different angles and split and cleared from worksites using these specialized tools.
Especially common in demolition, cutters act as hydraulically powered jaws to slice through a building or other large object quickly and precisely. When combined with tilting abilities the pinching power of cutters can be used for swift demolition and, at the control of a capable operator, even onsite sorting like pulling rebar from concrete while a structure is being demolished.
Whether you’re an expert excavator operator just enjoying a little excavator animation or an inquisitive construction equipment reader, hopefully you’ve found our information on excavator arms interesting and fun. An excavator is a common machine at worksites and seeing it in action makes clear that its design — at the hands of a good operator — is the reason why it is so often an indispensable resource.
If you’ve arrived here in search of an excavator part for your arm (or anywhere on your machine), give us a call or fill out our form. As a top salvager of excavators, our inventory is hard to match and with the expert parts knowledge of our Parts Specialists and robust connections to parts suppliers around North America, often the fastest path to your solution is a quick call to our team.
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