Compact Focus: Excavators >1.5 to 2 metric tons
| June 12, 2007 |
Question: What earth-moving system were compact excavators in the >1.5-to-2-metric-ton class designed to replace?
Answer: About six adult men with shovels and a wheelbarrow.
That tells you all you need to know about the appropriate applications for these small but powerful earthmovers. In some cases, notes Keith Rohrbacker, product specialist, Kubota Tractor, compact excavators in this class replace walk-behind trenchers, but the emphasis remains the same. “Most contractors want to own or rent the largest excavator they can tow and will fit on the jobsite,” Rohrbacker explains. “Typically, machines in this class are used in plumbing, sewer, utility or home repair applications.”
The advantages compact excavators offer over shovels and wheelbarrows are obvious: Not only can the machine work a lot faster and do a higher volume of work, but there are fewer payroll checks to write at the end of the week. That’s an attractive incentive for a small business. Compact excavators may not be able to compete with walk-behind trenchers on long excavation runs because even the longest-reach excavator eventually has to stop digging and reposition itself farther down the trench line. But they match the productivity of trenchers in short run applications.
The real advantage of compact excavators is their extreme versatility. Machines in this class typically have digging depths from 6 to 8 feet – and aren’t restricted to merely digging in a straight line. And then there’s the attachment angle: Thanks to their relatively powerful hydraulic systems, these machines can run a host of attachments, including hammers and breakers for light demolition work, thumbs for cleanup jobs and rollers for trench compaction. Retractable undercarriages allow them to contract to widths as small as 40 inches to get through tight areas. Once the machine is in position, the tracks are expanded out to their working width.
“If you need a piece of equipment that will mainly dig or reach with an attachment, then a compact excavator is a perfect match because these machines have such a long reach,” says Mike Lumbers, senior product manager, Ditch Witch. “If you need to haul a lot of loose materials or run what I call more powerful auxiliary attachments, then you need something besides a compact excavator – applications that require ground drive, for example. Compact excavators have a ground drive undercarriage, but it’s designed to get the machine from point A to point B and let it get to work.”
“Often, the versatility of a compact excavator allows it to be the only machine on a job,” adds Dan Bruch, product manager, Caterpillar. “Compact excavators, however, also often work in conjunction with other machines.” Excavators in this class are a natural fit with compact backhoes, wheel loaders and rubber track loaders, but Bruch says the most common pairing is with skid-steer loaders. The two machines work well together in a host of applications and are most effective at jobs such as digging a pool. The compact excavator can dig while the skid-steer loader removes the material and loads it in a dump truck.
“In many cases the use of compact excavators is changing the make up of fleets,” says Lance Mathern, product specialist, Bobcat. “We’re seeing more contractors fine tuning their operations, replacing under-utilized pieces with smaller, more efficient ‘job-matched’ machines.”
These contractors typically are adopting a “system” approach, Mathern says, such as using the compact excavator/loader teams referenced by Bruch to replace single-piece units like large backhoes. The realignment trend Mathern cites doesn’t end there. He says a growing number of contractors are adding smaller excavators to their fleet, specifically to complement larger machines. In some cases the smaller excavator can minimize the necessity of subcontracting out work, thus reducing reliance on a third party.
Low machine sounds levels are crucial, especially when working in confined areas.
Differing designs can affect features, transport and performance
According to Dan Rafferty, product manager, compact excavators, JCB, the four most-looked-at specifications are unit weight, digging depth, horsepower and bucket breakout force. “These machines can easily be towed behind a 1/2-ton pickup truck, so weight is an important consideration for many small contractors,” he advises. “But don’t forget to examine machine reach at ground level and lift capacities over the front and sides of the machine – these are all productivity enhancers.”
Rohrbacker advises contractors to make sure the machine has a large, comfortable operator’s station and auxiliary hydraulic hoses and valves as standard equipment. “Low sound levels are essential, especially when you’re working in close, confined areas. Check out the machine’s fuel consumption figures and see if it has protected hoses in its boom and arm structures. Dust is always bad for an engine, so look for dual element air cleaners as well.”
In addition to conventional designs, many OEMs now offer zero-tailswing models in this class. “The great thing about zero-tailswing machines is you don’t have to worry about colliding with buildings or other structures when swinging the unit’s upper structure,” notes John Kuyers, product manager, Vermeer. “That’s because the rear of the machine pivots within the track’s width greatly reducing – or even eliminating – the chance of hitting obstacles.”
But not every OEM is sold on zero-tailswing models in this size class. “You get a little bit more lifting and digging ability from conventional design machines,” Takeuchi’s Ross notes. “And the operator stations on these models tend to be larger – you have more available leg room – because the engine compartment is behind you instead of underneath you.”
Zero-tailswing units are also a bit heavier than conventional models, Kuyers says. That’s because designers negate the missing counterbalance by putting more weight into the tractor body. He notes that the weight difference is usually minimal, but it could affect your transportation requirements and ought to be looked
at if you’re trying to decide between the two machine types.
Ross says a conventional-design compact excavator has a more stable digging platform. “The only time you really need a zero-tailswing model is when you’re really jammed in tight digging between two buildings. But even then I’m not sold on them in this size class,” he says. “These excavators are so small to start with they’re already accessible enough to do everything a zero-tailswing design can. You can use a conventional-design excavator with an offset boom every bit as effectively as a zero-tailswing machine in tight conditions. Plus you get more craning ability and more breakout force because the weight is distributed better and the balance is better.”
Kuyers believes both models have a role to play on jobsites. If you’re in the market for a compact excavator, he suggests demo’ing both types to see how they perform. Once you’ve got a handle on that, consider the skill set of the operator – even if that means asking yourself some tough questions if you’re the one on the joysticks most of the time. “Are you the type of guy who doesn’t always pay attention to the obstacles around him?” he asks. “If so, I’d recommend a zero-turn machine. If you’re more in tune with your surroundings, then a conventional machine is your best bet.”
Many manufacturers are beginning to offer zero-tailswing models in this class, to further enhance their effectiveness in tight working areas.
Realistic-feel controls and
simultaneous machine functions
help operators work quickly
Even though they average 15 to 20 horsepower, these machines are quite productive. Most models generate more than 3,000 pounds of bucket breakout force. They can also lift up to 700 pounds over the front end of the machine, and up to 500 pounds over the side.
If you’ve never operated a compact excavator, you’ll probably notice the controls are relatively sensitive the first time you try one out, says Kendall Aldridge, product manager, IHI. “Some compact excavators, including our models, feature hydraulic pilot controls and a four-pump hydraulic system comprised of two piston and two gear pumps working in tandem.”
Aldridge says a four-pump hydraulic system is a productivity boost for compact excavators because they give you the ability to enact multiple boom, stick, arm and swing functions simultaneously. “The pumps react to your control inputs and make sure sufficient power is supplied to the respective cylinders on demand. It lets operators be smoother and more precise when working, and saves time and money on a job.”
Other OEMs have replaced hydraulic gear pumps with variable displacement pumps. “Gear pumps were the norm in the past and required lots of horsepower to operate,” Rohrbacker says. He adds that variable displacement pumps do the same work as gear pumps, but require less horsepower to do so. So, an excavator with a lower horsepower engine can work as hard as a gear-pump-equipped machine. In addition, Rohrbacker says variable displacement pumps give you lower fuel consumption and sound levels and a larger operator’s space since the engine and the hydraulic pumps are smaller.
Pilot joystick controls also contribute to smooth machine operation. Mike Ross, product manager, Takeuchi, says that’s because they give you much better feel for what the machine is doing. “Pilot controls have no mechanical linkage connecting them to the gear pumps,” Ross explains. “As a result, they’re a lot easier to operate – and there are no wear items to worry about. You’re basically dealing with a low-pressure hydraulic line tied into the valve bank, directing flow, pressure and oil to the different machine functions.”
In addition to the more realistic feel pilot controls give you, Ross says they also give you fine, feather control and the ability to do precise digging work. “This is a great feature when you have to dig around existing lines or pipe in the ground, or when you’re installing utilities behind another contractor,” he says. “The precision pilot controls minimize the chance of damaging existing utilities.”
But because many contractors find compact excavator controls to be “jerky” the first time they operate one, Aldridge recommends running the unit at approximately 1/4 throttle until you get used to the sensitivity of the controls.
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