Essential Excavator Parts and Their Functions
Table of Contents
Your job is at a standstill because an excavator just went down. You need maintenance to get there quickly, so you don’t waste any more time than necessary. Knowing an excavator’s parts and functions allows you to talk to your mechanic about the problem in a way he’ll understand. Otherwise, you’ll lose valuable time, and money, while they figure it out.
This article will spell out the key excavator parts and what they do, giving you an overall picture of how this versatile machine works.
What are the important parts of an excavator?
An excavator has three main areas: the undercarriage, the house or cab, and the hydraulic system.
The undercarriage contains the tracks or wheels used to move the excavator, a motor that makes the tracks move, and the swing gear that allows the machine to rotate in a full circle.
The house or cab is where the controls are located. It also contains the counterweight that helps keep the machine from tipping over, the main engine, fuel tank, and the main control valve, or MCV, that directs hydraulic fluid to the boom and arm.
The hydraulic system starts in the cab and runs through the boom and arm, bending, extending, and retracting according to what the operator says. The system includes cylinders, hoses, pumps, and a fluid tank.
Excavator parts and their functions
Let’s look at an excavator's inner workings, broken down by location on the machine.
Undercarriage
The undercarriage is the bottom section of an excavator and is responsible for providing stability and motion. It houses:
- Tracks or wheels – An excavator’s wheels or tracks are usually high-strength steel or steel-reinforced rubber. Tracks work well on uneven, rough terrain, while wheels do better on smoother surfaces.
- Track frame – Similar to axles on vehicles, the track frame is where the tracks attach to the undercarriage.
- Track pad – The track pad helps prevent excess noise, vibration, and damage to the body of the excavator, while also providing traction during operation.
- Track chains – Similar to bicycle chains, track chains help the excavator move.
- Track shoes – Track shoes are the individual pieces of a track that help pull the excavator along.
- Track bolts – Track bolts link the shoes together to form the track.
- Rock guards – Rock guards attach to the track and help prevent damage from debris.
- Sprockets – Sprockets run between the track chain links and help move the chain and track.
- Idler – An idler is a large metal wheel at the front of the machine that helps guide the tracks, keeping the excavator moving smoothly by ensuring proper track tension.
- Rollers – Two sets of rollers in the undercarriage align the track chains and move them between the sprocket and idler.
- Travel motor – The travel motor controls track movement. The hydraulic system sends fluid to this motor, which is converted into rotational force that drives the tracks forward or backward.
- Swing gear or drive – This feature allows the top portion of the excavator to move in a 360-degree rotation without moving the tracks or wheels.
House or cabin
The house, cabin, or cab is the main control hub for the excavator. It contains the following components:
- Main controls – An excavator’s operational controls, steering mechanisms, and safety measures are contained in the cab. Various joysticks, pedals, and buttons operate different functions and movements.
- Rollover protective structure (ROPS) – Like a vehicle roll cage, the ROPS helps protect the operator during a rollover.
- Counterweight – The counterweight sits at the back of the house and counterbalances the excavator’s boom, arm, and bucket when extended and loaded, preventing it from tipping. It’s made of heavy iron or steel and can weigh several tons, depending on the size of the machine.
- Engine – The excavator’s engine is usually located in the rear of the house and typically runs on diesel fuel. It powers all the systems, including hydraulics, tracks, swing drive, and other components.
- Hydraulic fluid tanks – These tanks hold the liquid that helps move the boom, arm, and bucket.
- Fuel tank – The fuel tank stores the fuel for the main engine, usually diesel.
- Main control valve (MCV) – The main control valve connects the engine and hydraulic system. It’s located near the hydraulic pump and has multiple spools that direct fluid flow.
Hydraulic System
The hydraulic system, which is comprised of cylinders, hoses, and pumps, moves pressurized fluid through hoses to the cylinders connected to each component.
- Boom – The boom is the front part of the excavator attached to the house. It’s typically mounted at the machine’s base and holds the arm. Mono-booms are standard, but articulated or knuckled booms are available and provide flexibility in confined spaces.
- Arm (also dipper or stick) – The arm holds the bucket or other attachment and is attached to the boom. It can be a fixed length or telescoping, with customized lengths and shapes to meet different needs. Longer arms provide deeper digging, while shorter arms are better for heavy lifting.
- Bucket – Buckets are available in several sizes and shapes. While a traditional digging bucket will work for most applications, if you’re digging up rock or another hard substance, a rock or frost bucket may be more appropriate.
- Cylinders – When filled with fluid, the hydraulic cylinders create the pressure that moves each component.
Attachments
A wide variety of buckets and attachments are available to change the type of work or adapt to specific conditions. These are easily changed using a coupler system. Attachments include:
- Trenching buckets – Dig narrow trenches for utilities. It is also available in micro size (or fiber optic) for trenches only a few inches wide.
- V buckets – Creates clean V-shaped trenches; used for cables, pipes, and ditches.
- Rock buckets – Extra tough for compact or hard surfaces; its sharp teeth are perfect for asphalt and stone.
- Skeleton buckets – Back has slots or a grid to allow fine materials to pass through. Used for sifting out larger materials.
- Rake riddle buckets – Has long teeth to rake through dirt and soil. Used to separate aggregate and trash from a load.
- Grading buckets (also called finishing or trench cleaning buckets) – Used for smoothing and leveling a surface; it's dragged along the ground to distribute fine materials.
- Clean-up buckets – An all-in-one finishing bucket that levels surfaces and hauls away large loads.
- Thumbs – When paired with a bucket, used to pick up and carry loads.
- Grapples – Used to pick up and carry loads.
What is the working principle of an excavator?
An excavator works through hydraulic hoses, pumps, and motors. When the operator moves a control in the cabin, the system activates, driving the boom, arm, or bucket as desired. The counterweight in the back of the cabin helps offset the weight of the equipment and the load, helping to prevent tipping.
What are the two excavator control patterns?
There are two excavator control patterns, ISO and SAE. Note that you can change the control pattern with many modern machines so it can be customized to the operator.
- ISO – also called CAT or excavator controls
The right lever controls the boom and bucket, left lever controls the arm and swing
- Right-hand lever – boom and bucket
- Toward operator – Raise boom
- Away from operator – Lower boom
- Left – Curl in or close bucket
- Right – Curl out or dump bucket
- Left-hand lever – arm and swing
- Toward operator – Bring arm toward you
- Away from operator – Extend arm away from you
- Left – Swing left
- Right – Swing right
- SAE – also called John Deere or backhoe controls
The right lever controls the arm and bucket, left lever controls the boom and swing
- Right-hand lever – arm and bucket
- Toward operator – Bring arm toward you
- Away from operation – Extend arm away from you
- Left – Curl in or close bucket
- Right – Curl out or dump bucket
- Left-hand lever – boom and swing
- Toward operator – Raise boom
- Away from operator – Lower boom
- Left – Swing left
- Right – Swing right
What is an MCV in an excavator?
The main control valve (MCV) controls the flow of hydraulic fluid throughout the excavator’s system. It directs the fluid to the particular cylinder to create the movement as instructed by the operator. For example, the fluid would be dispatched to the cylinder near the arm, which extends it to lift the arm. The liquid is drained from that cylinder to retract the arm, moving it back to its original position.
Do the parts differ for different types of excavators?
Most excavators have similar parts, although they may vary by size depending on the machine's capacity and size.
Unfortunately, each brand uses its own proprietary parts, making it difficult to swap from one manufacturer to another.
Which of the parts are the most expensive, and which are cheaper?
The most expensive parts to replace on an excavator include the boom, arm, hydraulic cylinders, engine, tracks, and the main control valve.
Consumable items like switches and valve hoses are less expensive to replace.
Used excavator parts can replace damaged hydraulic cylinders, arms, cab body panels, buckets, and attachments. The only places you wouldn’t want to have used parts are excavator undercarriage parts and the cab itself. The ROPS must be certified, and damaged units cannot be recertified, so you’ll have to get a new cab from the manufacturer. Used excavator parts for sale can be found at local machine parts stores.
New excavator parts can be ordered directly from Chadwick-BaRoss.
Contact our team to learn more about excavators, how they work, and their maintenance requirements or to purchase equipment or parts.