Hydraulic excavators in the >12 to 14 metric tons classes are the first “big” machines available to contractors in most manufacturers’ lineups. Because they’re not high-volume earthmovers, these size excavators find themselves employed in extremely varied applications. They are most popular among utility contractors who use them for trenching and pipelaying operations.
But they can also be found digging foundations on residential jobsites, doing site prep work for commercial buildings or demolition or landscape work. And the beauty of these excavators is that thanks to their easy transportability and multiple attachment capabilities, they could very well move from one of these jobs to the other in the course of a week.
Compact radius design bolsters
performance in tight surroundings
While the basic role of these machines is set, they have been undergoing something of a transformation in recent years. Excavators in these size classes – and the types of working conditions they’re typically placed in – make them ideal candidates for compact radius design models.
Unlike conventional excavator designs, which rely on an extended counterweight behind the machine for balance and higher lift capacities, compact radius models feature a design that allows more of the structure of the excavator to be contained within its track radius.
One example is Link-Belt’s 135 MSR Spin Ace, which Loren Haney, product manager, LBX, says is a good match for many of the applications these excavators work in. “These machines can turn in one lane of traffic,” he says, “and they can work right up alongside a wall in residential construction or landscaping jobs. They increase productivity because you don’t have to constantly check the machine’s rear end to make sure you’re not about to hit something. They’re safer, since there’s less chance of an accident when you’re doing roadwork, and you don’t have to worry as much about repairing damages to the machine or to a structure that’s hit.”
Because contractors can be a conservative lot, many manufacturers continue to offer both conventionally designed excavators and compact swing models. “There’s some fear out there that compact radius machines don’t have the lift capacities of the older models, because it appears the counterweight isn’t there,” says Dave Wolf, marketing manager, heavy equipment, Case. “But that’s not so. You don’t lose much – if any – machine counterweight with a compact radius excavator because it’s still there. The new design simply pulls the weight in and distributes it upward on the rear body. Usually, machine lift capacities remain close if not the same.”
“Actually, lift capacities are determined by the size of the machine, how far out the machine is from the hole, how deep the hole is and how heavy the machine is,” says John Balkema, North American marketing manager, small tracked excavators, Caterpillar. “All of these factors are directionally proportional to the machine’s digging performance. But in extremely close digging jobs – where the excavator is right up against the hole – a compact radius machine’s more compact center of gravity will give you tremendous lift advantages because all the weight is at your disposal. It’s not hanging off the back end too far away to help you lift.”
Spec long sticks for reach, short sticks for power
Most manufacturers offer excavators in these classes with a standard size boom and a variety of stick (or arm) lengths. Because some very basic geometric principles apply to excavator boom configurations, understanding the plus and minus associated with different stick lengths is crucial for productivity. “Generally speaking, a smaller stick should be used in heavy digging and loading applications,” says S.M. Yang, excavator product manager, Volvo Construction Equipment. “Short sticks provide you with higher breakout and prying forces. Longer sticks should be used in applications requiring extra dig depth and reach, such as pipe laying work.”
“A lot of contractors like to fit their excavators with a long arm and a big bucket, which we try to discourage,” Wolf says. “Unless that contractor is in a reach-intensive application, he’s compromising machine performance. Excavators with a long arm and big bucket perform poorly because the machine’s weight is pushed out further from its center of gravity. If you’re digging, it’s in your best interest to keep the machine’s overall envelope tight.”
“Remember that if you’ve got a 10-foot arm on your machine, and you replace it with an optional 11-foot arm, you’re going to lose 10 percent of the arm force generated by the arm cylinders,” cautions Haney. “It’s an acceptable loss in most deep reach applications. But it also means that you have to pay attention to spec’ing other components, which can also lessen your machine’s productivity. By itself, a 10 percent loss isn’t much. But if you lose 10 percent of your breakout forces on the stick, and then 15 percent somewhere else, your excavator has suddenly lost 25 percent of its available power.”
Hydraulic power for attachments, horsepower for digging
North American contractors are conditioned to check horsepower figures when evaluating a new piece of equipment. But that may not be the best gauge of an excavator’s potential productivity, Balkema warns. “Both horsepower and hydraulic capability are crucial on a productive excavator,” he says. But prioritizing horsepower is only logical if you intend to use the machine in high-volume, dig-and-dump applications.
If your excavator is digging and loading trucks, then Balkema says to place a premium on horsepower, which is going to help the hydraulic system power through the soil, and give you faster swing and boom speeds for loading trucks. “On the other hand,” he says, “if you intend to use your excavator with a wide array of work tools, you need to spec a hydraulic system with the power, capacity and flow rates to handle the attachments you’ll be using.”
Vince Whelan, product manager, tracked excavators, JCB, says you’ve got to optimize your hydraulic system options if attachment use is important to you. “There are a variety of choices available,” he says. “And these choices basically depend on the types of attachments you’ll be running.”
According to recent surveys conducted by attachment manufacturers, 75 percent of excavators in the >12 to 14 metric tons classes will be equipped with a hammer at some point in their productive lives. If you’re planning on extensive hammer use, Whelan says you’ll need an excavator with an auxiliary hydraulic kit, including full piping to the coupler. Low-flow piping is available for contractors who want to run slower, high-torque attachments like roto-tillers. “And thumbs are increasingly popular on these models as well,” he says. “Any reversible-action attachment – like a thumb or grapple – requires bi-directional hydraulic flow. This type system lets hydraulic oil pump in and out of the circuit, allowing reverse movement on a tool.”
The latest generation of attachments is making even harder demands on excavator hydraulic systems in the >12 to 14 tons classes, according to Del Wayne, regional sales manager, Daewoo. “Recently attachments such as rotary drills have found their way onto excavators in these classes,” Wayne notes. “If you’re considering spec’ing these attachments, bear in mind they have very high flow requirements and demand maximum oil cooling efficiency.”
Other attachments, such as concrete crushers, operate at high pressures to actuate quick response as they open and close. Tilting buckets require a high-speed system to deliver finesse control when used in a fine-grade application. If you’re planning on using these attachments, their combination of power, speed and control and the hydraulic demands they place on your machine need to be carefully considered at the time of purchase.”
The technical requirements and operating instructions for the attachment will tell which type of hydraulic system it requires. Beyond that, Eric Wilde, product manager, Komatsu, says it’s a simple matter of matching the excavator’s performance with the attachment’s recommended hydraulic flow and pressure rates.
“And make sure the attachment’s not too large for your machine,” he says. “Just because your excavator can pick up an attachment doesn’t mean it can work with it effectively. At best, an oversized attachment won’t work properly. In a worst case scenario, it will upset the machine’s center of gravity and increase the risk of tipping.”
Remember, coupler width factors into your boom/arm calculations
Of course, if you’re going to run a variety of attachments, it’s sensible to equip your excavator with a hydraulic quick coupler to allow fast and easy attachment changes. But although the benefits of hydraulic couplers are well documented, they can negatively impact an excavator’s overall performance.
“When you put a coupler on an excavator, you’re adding at least 10 inches of extra reach to the arm – a foot if you’ve opted for a universal style coupler,” Haney says. “That doesn’t sound like much, but if your machine is equipped with long arms, you’re not only increasing its overall length, but you’re adding extra weight to the elongated configuration. It’s quite possible you’ll not only lose another 10 percent of your machine’s breakout force.”
And, again, the coupler’s extra weight will increase the machine’s chances of tipping. “So, if you’re going to use a coupler, I’d recommend that you always use smaller arms,” Wolf says. “The tighter you can keep your excavator’s working envelope, the more productive and safer you’ll be.”
Proper bucket sizing vital for profitable earthmoving
Attachments may garner all the attention, but at its heart, an excavator is a digging machine. No matter what boom and arm configuration you decide to go with, the bucket is its business end. And spec’ing the correct type of bucket for the soil and job at hand can go a long way toward putting money in your pocket. “There are a wide variety of buckets to match any customer need,” notes Mark Wall, business analysis manager, Deere. “But the wrong bucket can cost you money in a variety of ways.”
One example Wall points to is using an excessively wide bucket in trenching applications. “A wide bucket causes you to remove too much material when excavating,” he explains. “That not only wastes time, but you could end up using additional bedding material to refill the trench, which comes out of your pocket.”
A big bucket can also get you into trouble if you’re trying to excavate heavier soils. “In Savannah, Georgia, you have to deal with heavy, wet, Georgia clay,” Whelan says. “The mass of that clay in a bucket is huge. Contractors there tend to excavate using 2 cubic-yard buckets instead of more common 4 cubic-yard ones. Even though the bucket is smaller, they can get the same weight of material in the it, without having to pull the added mass of a larger bucket through the ground.”
But using too small of a bucket won’t let you get the maximum productivity from your excavator. Go too small, and you’ll have to perform more cycles to get the same amount of work done as you would using a correctly sized bucket. “It’s a balancing act,” Balkema admits. “If you want quick, fast loads, smaller buckets are the way to go. But track your progress carefully. You might be getting double the cycles in an hour’s time – but you might only be getting a third of your machine’s potential bucket capacity on each pass.”
And finally, Wilde cautions, don’t use a bucket simply because tradition dictates it. “We see that some in certain areas of the country,” he says. “In parts of Ohio, contractors always request large mass excavation buckets, when they’d be better served spec’ing a narrow-profile bucket for the heavy soil in that region. Nobody knows why – it’s always been that way. Be willing to try some new approaches.”
