Machinery Insights: 16 Excavator Parts You Need to Know

Understanding the various components of an excavator is crucial, both for effective operation and for conducting proper maintenance and troubleshooting. While as an operator you may not require the in-depth expertise of a mechanic, having a basic comprehension of the machine's parts can greatly enhance your efficiency. Excavators, despite their diverse brands and models, comprise many standard components. These can primarily be divided into two sections: the upper structure and the lower structure. This article will dissect these vital parts, equipping you with the knowledge to effectively handle and preserve your excavator.

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Lower Structure of a Track Excavator

The lower structure, commonly known as the undercarriage, is essentially the base of an excavator. This segment is responsible for ground contact and mobility. Focusing on track excavators, also known as crawler excavators, we will delve into the five principal parts that constitute the undercarriage: tracks and track pads, rollers, idlers, sprockets, and the swing drive/slewing ring.

A view of the Kobelco SK220 crawler excavator's lower structure in action on a job site

1. Tracks and Track Pads

Tracks are fundamental to the mobility of crawler excavators. They are crafted from reinforced steel and include track pads or shoes of varying sizes. The outer edges, referred to as grousers, are designed to provide grip during movement. The linkage between these plates occurs through track bolts, forming a cohesive crawler system. This system is affixed to the excavator via a track frame, comparable to an axle. A track chain within the crawlers connects them to the sprocket and idler, ensuring continuous movement.

2. Rollers

Rollers are metallic wheels positioned on the undercarriage, serving to guide the chains between the sprocket and idler. There are two types: bottom and top rollers, both crucial for maintaining chain alignment. In some cases, rollers are fitted with rock guards to shield against debris and rocks.

3. Idlers

Idlers are larger wheels that play a critical role in guiding the undercarriage. They work alongside rollers and sprockets to ensure smooth track operation. Their size and positioning are vital for the efficient movement of the excavator.

4. Sprockets

Sprockets function similarly to large bicycle gears, interfacing with the excavator track chain links. Their main role is the propulsion of the chain, moving the machine either forward or backward.

5. Swing Drive/Slewing Ring

The swing drive and slewing ring are essential for the excavator's rotational capabilities. They facilitate the upper structure's ability to pivot in relation to the lower structure. These components operate hydraulically and require consistent greasing for optimal function.

Upper Structure of a Track Excavator

The upper structure, often referred to as the excavator's "house," amalgamates the carbody and the boom-and-arm mechanism, forming the core functionality of the machine. Here, we will examine 11 primary components that comprise the upper structure, progressing from rear to front.

A view of the Kobelco SK220 track excavator's upper structure in action on a job site

1. Counterweight

The counterweight is essential for ensuring balance during excavator operation. It averts the risk of tipping while digging. The weight of the counterweight typically correlates with the total operating weight of the excavator. For example, a CAT 395 excavator, with an operating weight of 94 tons, is equipped with a 15.5-ton counterweight. Likewise, a Komatsu PC400 excavator, weighing 43.3 tons, features a 9.2-ton counterweight.

2. Engine Compartment

This compartment is more than just a housing for the engine; it serves as a central hub for several significant components:

• The fuel tank, which stores the necessary diesel fuel.

• The engine, conveniently located near the cab for ease of maintenance, acts as the powerhouse of the excavator.

• The hydraulic oil tank, vital for the hydraulic mechanisms.

• The main control valve connects the engine to hydraulic devices, regulating oil pressure.

3. Cabin

The cabin serves as the command center for the excavator, housing essential controls and safety features. Depending on the model, cabs may rotate 360 degrees to provide maximum visibility. The cabin is equipped with:

• Main control mechanisms that vary by model.

• ROPS (Rollover Protective Structure) for protection during rollovers.

• FOPS (Falling Object Protective Structure), a reinforced steel framework to safeguard against falling debris.

4. Boom Cylinder

This component connects the boom to the carbody, controlling the vertical movement of the boom.

5. Boom

Attached to the cab, the boom serves as the forward-extending part that supports the arm. It is crucial for the digging mechanism's operation.

6. Arm Cylinder

The arm cylinder connects the arm to the boom, enabling the arm's extension and retraction.

7. Arm (Dipper or Stick)

This element of the excavator connects to the boom and carries the bucket. It is essential for accurately positioning the bucket during excavation tasks.

8. Boom/Arm Linkage

This assembly, consisting of pins and bushings, links the boom and arm, requiring regular greasing for smooth, noise-free operation.

9. Bucket Cylinder

This cylinder links the arm to the bucket, enabling digging and dumping functions.

10. Arm/Bucket Linkage

This mechanism connects the arm and bucket, facilitating their movements.

11. Bucket

The bucket is the primary earthmoving tool situated at the end of the arm. Standard excavators typically come with buckets, and regardless of the attachments used, the basic operation remains consistent.

To deepen your understanding of an excavator's design, we have prepared an informative infographic that summarizes all discussed components in both the lower and upper structures of a medium KOBELCO SK350 track excavator.

Excavator components: lower and upper structures of a medium KOBELCO SK350 track excavator

FAQs About Excavator Parts

What is the most commonly replaced part of an excavator?

The most frequently replaced parts are generally the tracks and track pads, primarily due to their consistent ground contact and the resulting wear and tear from movement.

How often should the hydraulic oil be changed in an excavator?

Typically, hydraulic oil should be replaced every operating hours; however, it is advisable to consult the manufacturer's guidelines specific to your model.

Can the bucket of an excavator be replaced with other attachments?

Absolutely, excavators are designed to accept a variety of attachments in addition to buckets, including breakers, grapples, and augers, tailored to specific job requirements.

What's the purpose of the counterweight in an excavator?

The counterweight plays a pivotal role in sustaining balance. It counteracts weight during digging and helps to prevent the excavator from tipping over.

If you’re an enthusiastic excavator operator or preparing for some maintenance, our interactive excavator diagram is designed to assist your understanding of this essential machine.

Excavator Parts Diagram

Click a part or a label to delve deeper into its function within an excavator or to search for the specific part at H&R.

 

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Cab

The elaborate cab of the excavator is the operator's control station. Controls for both machine movement and attachment manipulation are found here, typically involving various pedals, levers, and joysticks. Modern designs often integrate touchscreens and displays for enhanced feedback and input.

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Boom

The boom extends forward from the excavator's house and is a crucial part that determines digging depth and reach. There are various designs, including knuckled and long-reach booms, enhancing flexibility.

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Boom Cylinder

The hydraulic cylinders governing the boom's movement are pinned to the house and boom, enabling elevation and lowering actions.

Learn More About Cylinders 

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Stick

This arm section connects the boom to attachments, incorporating a system for control from the cab. A longer stick may be used for greater reach, while a shorter one can enhance digging force.

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Stick Cylinder

Controlled via hydraulic mechanisms linked to the boom, the stick's hydraulic cylinder manages the pivoting of attachments.

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Bucket / Attachments

While buckets remain the primary attachment type on excavators, a wide array of attachments is available for diverse tasks like digging or transporting materials.

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Bucket Cylinder

This component allows the operator to control the bucket's actions and is connected to both the stick and the bucket. Extending or retracting adjusts scooping and dumping movements.

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Linkage

For more information on excavator bucket, please do not hesitate to reach out.

Linkage, or simply links, are robust metal bars connecting different parts and attachments to the stick using pins for controlled movement.

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Engine

At its core, an excavator's engine converts energy from diesel into motion, supplying power to all machine components through direct and hydraulic energy methods.

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Main Hydraulic Pump

The main hydraulic pump converts mechanical energy from the engine into hydraulic energy, powering vital components that rely on hydraulic force.

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Main Control Valve

Hydraulic valves manage the pressure and flow of hydraulic fluid, intricately controlling machine and attachment movements.

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Slewing Ring

The slewing ring connects the upper house with the lower undercarriage, enabling independent movement between the two sections.

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Swing Drive

The swing drive, mounted to the house, comprises a swing motor and gearbox, providing the necessary torque for movement along the slewing ring's path.

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Travel Motor

The hydraulic travel motor generates motion for the tracks, paired with a final drive gear box located at the rear of the tracks.

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Final Drive

Final drive systems convert power from the drive train to the tracks using gears that decrease speed while increasing torque.

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Sprocket

Sprockets engage with the excavator's track segments, driving the machine forward by pulling the track in a specific direction.

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Front Idler

This large wheel at the front of the track group maintains track tension and guides the track along its required path.

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Track Springs

These large springs absorb impacts and keep tracks properly tensioned, often in conjunction with a grease cylinder.

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Bottom Rollers

Short, rolling cylinders located within the tracks bear the excavator’s weight and guide the track’s path.

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Track Groups

Designed for various ground conditions, tracks provide exceptional grip and stability, with options for metal, rubber, or hybrid designs. Increasingly, some excavators utilize wheels for faster transport.

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We trust that the information in this diagram, along with the concise definitions provided, will assist you in your quest for excavator knowledge. For any part solutions for your own excavator, our expert Parts Specialists are available to help connect you with our comprehensive and ever-growing inventory. Don't hesitate to reach out or request a quote.

 

Excavator Parts Diagram Image

An excavator diagram highlights important components and their locations.

For additional buy excavator quick coupler information, please feel free to contact us for professional insights.