All About Excavators

Excavators are indispensable equipment pieces in the earthmoving business. They’re also invaluable for general construction and utility work, demolition and scrap businesses, quarry and aggregate operations as well as handling waste and recycling products. If there’s material to move, no doubt you’ll find an excavator nearby.

It’s not just a question of using an excavator to dig, load or spread. It’s additional questions like what excavator types, what sizes, what power and what attachments you’ll find around excavation jobs. There’s no such thing as a one-size-fits-all application when it comes to excavators.

It’s easy to get confused when researching excavators. You’ll find several the different types of excavators available, such as mini-excavators, backhoe excavators, extended-reach excavators and even excavators built to use suction rather than teeth. Excavators also have complex parts and a surprising array of attachments available.

If you're considering renting or using an excavator, get the full story on these dependable digging tools.

Jump to a section:

• History of Excavators
• Parts of an Excavator
• Types of Excavators
• Excavator Uses
• Excavator Attachments

History of Excavators

Mechanized excavators have been around for over two hundred years. The first steam shovel appeared in 1796. William Otis assembled a highly functional system of gears, chains, pulleys and cables to excavate dry earth. He patented the design in 1839. By the mid-1800s, his steam shovel invention was the backbone of railway construction. It could move 300 yards of material per day. A team of men with picks and shovels could only dig 12.

Hydraulic excavators, which also use steam power, date to 1882. Early prototypes built by Sir W.G. Armstrong & Co. featured steam-driven cylinders moving cables. By 1897, the Kilgore Machine Company introduced the Direct Acting Excavator. It was the first truly hydraulic excavator without chains or cables.

The Caterpillar Tractor Company entered the heavy equipment scene in 1925. Cat® machines were the first to use steel-linked tracks, which propelled their first bulldozers. It wasn’t long before Cat engineers put tracks under their hydraulic excavators, revolutionizing the earthmoving world.

Over the years, some excavators have set world records. The world record for the largest excavator goes to the Bucyrus RH400. The behemoth Bucyrus is 32 feet tall, 24 feet wide and weighs 980 tons. Its twin 4,500 horsepower engines drive a 65-yard bucket that moves 9,000 tons of material per hour.

The world’s largest land vehicle title also goes to an excavator. It’s the Bagger 293 mining machine, which tips the scale at 14,200 tons. It has a bucket wheel feature that handles 8.5 million cubic feet per working day. The machine is big enough to see in satellite photos.

On the small-scale end, there's the Cat 300.9D. It measures 28 inches wide and has a retractable undercarriage. It can sneak through a doorway to take on interior demolition challenges. Don’t think that small size means low power, though. The Cat 300.9D has a 13 horsepower engine running its tracks, bucket and blade.

Some excavators are designed with the future in mind. The Regolith Advanced Surface Systems Operations Robot (RASSOR) Excavator is a mini-mover that works in low-gravity environments such as those on the Moon, Mars, asteroids and comets. "Regolith" is the industry term for loose mineral material covering bedrock.

Excavators become more technically advanced each year. New generation machines have better fuel consumption, lower emissions, produce less noise and provide more power than earlier models. Advanced computer systems monitor the excavator’s health and assess operator performance.

Excavators are also much safer today than they were in early steam shovel years. Modern excavators have climate-controlled cabs with ergonomic controls. Advances such as zero-swing designs make them safer for nearby workers, too. And then there’s the wide assortment of work tools you can attach to your choice of an excavator.

Parts of an Excavator

Although a wide range of machine types and equipment sizes are available, most hydraulic excavators operate on the same principle. They use an engine, usually diesel-powered, to drive hydraulic pumps that pressurize oil and move drive and dig components. The main difference is the capacity and magnitude of the parts.

You’ll find three main component groups in hydraulic excavators. One is the drive system or undercarriage. The second area is called the house. It contains the engine, hydraulic pumps, counterbalance and control grouping. The third part is the excavating arm or the business end of the machine.

An excavator is truly a system where each component contributes to the machine’s overall operation. Excavators are a prime example of the whole being greater than its parts. No part of a hydraulic excavator is more important than the other. The components work as an excavating team, and without an individual player, the digging game would be lost.

1. The Excavator Undercarriage

An excavator’s undercarriage is its stabilization and propulsion unit. It contains the drive mechanism that lets the machine move forward, backward and sideways. The undercarriage is a complex system on its own with many interconnecting pieces that cooperate to drive the excavator around its workplace.

You might assume that all excavators have tracks. While most hydraulic excavators use steel or rubber tracks in their undercarriage, wheeled excavators do exist.

Here are the main parts in a track-equipped excavator undercarriage:

• Slew ring, swing gear and swing bearing. The slew ring, swing gear and swing bearing connect the excavator’s house to its undercarriage. Technically, this component area could be part of the house group, but it’s also built into the undercarriage. It is the turntable region of the excavator and lets the house revolve on the track assembly.
• Sprockets and idlers. Excavator tracks are an extension of the chain drive principle. The tracks are amplified links that turn within a sprocket and idler assembly. Sprockets are toothed gears that interconnect with the track links while idlers play a critical alignment role.
• Tracks, pads and drives. Excavator drives are motors that turn the sprockets and give motion to the track assembly. Tracks can be made of hard steel composition, designed for use in rough areas or they can be soft rubber for sensitive spots. You’ll hear the term “grouser pads” for the crossbars mounted on steel tracks that give the machine its traction.

2. The Excavator House

The brilliance of a true hydraulic excavator is its ability to revolve in a complete circle. Excavators differ from backhoes and their digger cousins because they can rotate 360-degrees without restriction. Backhoes can dig like excavators, but they’re limited to a 200-degree side-to-side movement.

An excavator’s house sits on a turntable joining the cab and engine to the undercarriage. The house also connects to the excavating arm, making it the central command and control center. It’s also the powerhouse where fuel energy gets converted to excavating force.

Here are the main components you’ll find in an excavator’s house:

• Excavator cab and controls. The cab serves as the operator’s seat and control point. Most modern excavators work on a joy-stick and foot pedal principle that keeps an operator’s hands and feet busy. Gauges and glass also occupy an operator’s vision and lets them see what’s going on. Cabs are also the excavator’s Roll-Over Protective Structure (ROPS).
• Engine and pumps. The vast majority of hydraulic excavators use diesel engines to drive their hydraulic systems. Excavator power varies from mini-machines with 13 HP engines up to hundreds of horses in big-class machines. Larger excavators have multiple hydraulic pumps operating primary and auxiliary systems. And every excavator, regardless of size, has its fuel and oil tanks secured in the house.
• Main control valves. While the diesel engine is the primary power source, it’s the hydraulic system that produces the excavating force. An excavator’s main hydraulic pump has a central control valve that regulates the volume of hydraulic fluid circulating in the system. The pump and controls also dictate the pressure held in the main and auxiliary hydraulic lines.

3. The Excavator Arm

Without the excavating arm, the machine would be an undercarriage-mounted house with only the ability to move its self about. But add an arm and the machine goes to work.

Excavator arms are ingenious inventions that work as a series of hinges. The arm component can raise and lower, open and close, and extend and retreat. Combined, the hinged arm components let the machine dig, bail, load, throw and place material. Here are the main parts you’ll find on an excavator's arm:

• Boom. An excavator’s boom is the largest part of the arm. Booms are the upper arm portion and are mounted to the house. The boom is controlled and powered by a hydraulic boom cylinder, which is part of the machine’s primary pressurized system.
• Stick. An excavator’s stick us also called a dipper or an arm. Regardless of terminology, the stick intermediates power from the boom to the bucket. Excavator sticks allow the arm assembly to hinge as a multi-function unit, and they’re powered by a hydraulic cylinder mounted along the boom.
• Bucket. The bucket is where work really gets done. The bucket is the third arm component, and it can take many shapes as well as numerous attachments. Common earthwork buckets are for ripping and cleanup, but you’ll find everything from rock hammers to compactors mounted on the arm’s bucket end.

It’s the combination of house, arm and undercarriage that put an excavator to work. The reach, lift and load capacity depends on a blend of the parts. It’s usually true that the larger the excavator undercarriage, arm and house, the more performance it has within a fixed time.

These marvelous machines have come a long way in design, power and capability since the 1800s. Today, excavators offer operators convenience and safety.

Types of Excavators

There’s no one type of excavator. You’ll see an array of earthmoving and material handling equipment labeled “excavator." The type of excavator you need has to match how you'll use it. For most excavator operators, that function can change rather quickly.

There are seven separate excavator types. Some cross categories and serve dual purposes, but these different types had specific purposes when the design and engineering teams thought them out. Here are the general excavator types you’ll find serving many industries:

• Crawling excavators. Crawlers are the most common excavators you’ll see operating across America. These are machines on tracks, and they’ve earned their name from an impressive ability to crawl about the harshest terrain and take traction on steep slopes. Crawling excavator sizes range from rubber-tracked mini-excavators up to huge equipment moving on steel tracks. Crawlers exert less ground pressure than machines on wheels, making them the excavator of choice for many jobs.
• Wheeled excavators. While crawlers leave a light footprint and have superb traction, they’re relatively slow when mobile. Swapping tracks for tires on the undercarriage increases an excavator's speed. Wheeled excavators move much faster than tracked machines. While they’re not as stable as tracked undercarriage due to a higher gravity center, wheels give the excavator excellent mobility and better transport times around or between job sites.
• Skid steer excavators. Most people associate skid steers with wheeled loaders and compact track loaders rather than real excavators. Don’t be too quick to dismiss these fast and versatile machines as being dig-capable. Many skid steers, multi-terrain loaders and tracked compact loaders readily accept work tool attachments like an excavation arm. You’ll find digging attachments that suit your skid steer and economically transform it into a compact excavator that can move a lot of material in a very short time.
• Backhoe excavators. There's debate over whether traditional backhoes belong in the excavator camp. Every backhoe holds an excavating arm on the opposite end of its house from the loader bucket. The main difference between a backhoe and other types of excavators is that a backhoe’s excavation mechanism can’t completely revolve. That’s a small hindrance when you’re operating a backhoe for its designed purpose.
• Long-reach excavators. Long-reach excavators are big-classed machines used in specialized situations. They have extended arm lengths with boom and stick measurements far in excess of conventional machines. Some long-reach equipment has over 100 feet of horizontal extension. They’re ideal for working across difficult watercourses and tricky demolition sites where the operator can place the machine in a strategical spot and reach out to their work from there.
• Dragline excavators. Draglines work well in mining situations. Before current hydraulic excavators with 360-degree rotation arrived on the market, many excavation companies kept a dragline or two in their fleet. These timeless tools operate on a boom, pulley and cable system where the bucket is dragged from a line attached back to the machine’s arm. Although conventional draglines don’t easily rotate, their huge capacity makes them a top choice for open area earthmoving.
• Suction excavators: At the end of the uncommon scale sit suction excavators. These unusual but practical equipment pieces do work that no other excavator design can handle. They move material by shooting a high-pressure water jet into the ground and creating a vacuum that sucks loose material through a hose into a hopper. Suction excavators are common in high-density urban work where they perform close-quarter utility work with little damage risk to adjacent property.

Each excavator type has its purpose. Whether you perform regular construction, build roads, demolish buildings or mine material in a commercial capacity, there is a suitable excavator available.

Choose The Cat® Rental Store for Excavators and Attachments

In many cases, it makes sense to rent your equipment to give you the versatility and flexibility you need without the commitment. That’s where The Cat Rental Store can help.

The Cat Rental Store is a nationwide network of dealers who specialize in top-end Cat equipment. We rent all types of excavators and tool attachments as well as a comprehensive inventory of related construction equipment. We’re here to help you source the most suitable machines for whatever task you’re tackling.

Let The Cat Rental Store specialists walk you through our excavator line and demonstrate how attachments can turn your basic machine into a value-added profit center. Call The Cat Rental Store today at 1-800-RENT-CAT or find a location near you.

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