Productivity Guide: Compact wheel loaders
| June 12, 2007 |
The evolution of compact construction machinery has given contractors the ability to fine-tune many of their earthmoving operations. Compact wheel loaders in the 60- to <80-net-horsepower class are primarily designed to be effective loading machines.
Given this basic strength, typical applications include re-handling loose materials, lifting and loading landscape materials, hopper loading at small industrial sites and moving materials at waste recycling facilities. "Other machines may be considered for these activities and the choice can be complex," notes Dan Bruch, sales support consultant, Caterpillar. "A telehandler can lift higher, but needs more space and costs more to purchase.
Skid-steer loaders cost less, but have higher tire wear and are less comfortable to operate.
Compact wheel loaders can do all these jobs, in addition to loading trucks with bodies up to 10 feet high." Because of their prominence in residential and landscaping applications, Bruch says considering the different amounts of wear and tear each machine inflicts on soil surfaces can be a good indicator of which machine is right for your type of work.
Des Jarvis, product manager, Atlas Construction Equipment, notes skid steers have been the traditional compact machine of choice in North America. He offers these guidelines for choosing between a skid steer and a compact wheel loader: First, gauge the available space in the area the machine will be working. If there is minimal room, then a skid steer is the best choice since it is a more maneuverable machine. But if there is ample room to operate a compact wheel loader in most cases your overall productivity will be higher. "This is due to the wheel loader's improved visibility, smoother travel, higher travel speeds and improved operator comfort compared to a skid steer," Jarvis says. Combined with those factors, he says compact wheel loaders also have higher gross load carrying capabilities than skid steers, which allow them to be efficient in load-and-carry, material-handling or hopper-loading applications.
Compact wheel loaders have an advantage over machine types like skid steers and telehandlers in that they are inherently easy to operate, says Brian Rabe, product manager, Mustang. "Operator skill level is the most overlooked aspect when considering any piece of compact equipment," he says. "But wheel loaders have controls similar to a car or truck. This simple, familiar layout allows almost any operator, experienced or not, to be productive from the minute they start operating the unit."
Another appeal compact wheel loaders have for many contractors is the fact they can see a job through from beginning to end. "These machines can start out clearing a lot and loading spoil material onto trucks," Jarvis explains. "With the number of attachments available, they can do material handling and site prep as the job advances, and do final grade work and landscaping as it winds down."
One final concern you must address as you choose between skid steers or compact wheel loaders is your transportation resources. "A compact wheel loader – as opposed to a skid-steer loader – requires the right trailer and proper hauling permits," explains Eric Wrinkler, product manager, New Holland. "If the machine is going to stay in the yard and you have a lot of lift and carry work to do over time, the compact wheel loader is a better value because you are going to be able to put a lot more hours on it. If you expect to move the machine to a different jobsite fairly often, a skid steer might be a more logical choice for your business."
Select the correct loader geometry for your application
Dave Wolf, product marketing manager, Case Construction Equipment, calls compact wheel loaders a logical next step for contractors looking to boost productivity without moving to full-size machines. “Skid steers are engineered to do a little bit of everything,” Wolf notes. “A compact wheel loader is a more application-specific design and many of the features they’re equipped with reflect this.”
One of these features is the loader linkage on the business end of the machine. Like their big brothers, compact wheel loaders can be spec’d with either Z-bar, parallel-lift or (in Volvo’s case) torque-parallel linkage systems. Each type of linkage is configured to excel in a specific type of application. Z-bar linkage, for example, features a heavy-duty cylinder and robust loader arms (arranged in a “z” shape) that is designed to deliver high breakout forces – an ideal choice for stockpiling and load-and-carry applications. Wolf notes some loaders in this class equipped with Z-bar loader geometry have breakout forces in excess of 15,000 pounds. Although Z-bar linkages can be fitted with quick couplers, and use attachments, their design configuration and the size of the center-mounted hydraulic cylinder can restrict forward vision somewhat.
Compact wheel loaders can handle limited truck- and hopper-loading chores.
If attachment use is a primary concern for your compact wheel loader, parallel-lift linkage is a better choice. This front-loader geometry features two lift cylinders, placed opposite one another on parallel-mounted boom arms. This isn’t as robust a design as Z-bar linkage, so breakout forces tend to suffer somewhat with a parallel-lift machine. That’s not to suggest these loaders can’t be effective in load-and-carry applications. But their real area of expertise is attachment use. The side-by-side loader arm design leaves more open space directly in front of the operator, giving you better visibility to the working point of an attachment or the front end of pallet forks. The dual cylinders and high-flow hydraulic systems also deliver more precise control and power to the attachment being used.
Volvo says its torque-parallel linkage combines the best features of Z-bar and parallel-lift configurations, providing high breakout forces and efficient attachment use in one design.
Specialized loader functions smooth out ride and increase cycle times
Other specialized features can boost a wheel loader’s performance on your jobsite. Among them are hydrostatic drives, return-to-dig, return-to-carry and ride control systems.
All wheel loaders in these classes are equipped with hydrostatic transmissions, which Bob Beesely, product manager, Komatsu America, says allows “on the fly” shifting and smoother directional shifting in load-and-carry applications than any other transmission type available today. “Hydrostatic drive systems are infinitely controllable,” Beesley explains. “They’re easy to operate because you do not have to do any mechanical shifting whatsoever. The transmission’s electronic control module monitors throttle input and automatically downshifts or upshifts to best match your working conditions.”
Typically, a hydrostatic drive system consists of a hydrostatic pump and motor system that delivers horsepower to the loader’s front and rear wheels via a driveshaft. Hydrostatic pump flow and engine speed are controlled by a foot throttle and transmission control pedal or lever, according to Jennifer Brigman-Westphal, compact wheel loader specialist, Volvo Construction Equipment. “The advantage for you is that a hydrostatic transmission will automatically stroke to a lower gear range for greater pushing power,” Brigman-Westphal says. “This gives you maximum torque at zero speed for efficient pile entry and exit, without any guesswork required on your part.”
Westphal-Brigman says hydrostat transmissions also allow inching, or creep, functions. “Depending on the return of the spring in the inching function to de-stroke, a machine can have a very smooth or abrupt start-stop,” she notes. “In either event, this function gives you infinite control over the wheel loader and allows you to maintain low speeds for precision grading work or using brooms, sweepers, snow plow or snow blades – all applications that require high engine rpm, but not necessarily fast travel speeds.”
Ride control is a feature that has migrated down from larger Case wheel loaders, Wolf says.
When activated, ride control meters an extra amount of oil into the loader’s hydraulic cylinders once boom movement has ceased. This hydraulic oil acts as a shock absorber as the machine moves across the jobsite by allowing the loader arms a minimal amount of up-and-down movement. In turn, the oil acts as a cushion, isolating the rest of the machine from any shock loads or vibrations generated by the boom arms.
“The obvious benefit is that you experience a smoother ride,” Wolf explains. “So you’re not as tired at the end of the day. At the same time, component life is extended because fewer shock loads are transmitted to the machine frame. Material retention in the bucket is better too, since there are no harsh jolts that can cause spills. This improves the loader’s overall productivity on the job.”
Brigman-Westphal points to return-to-dig and return-to-travel systems as additional production-enhancing wheel loader systems found on these compact machines. “Both systems use an electronic-hydraulic interface that allows you to easily set boom height and bucket angles for optimal digging and travel settings,” she explains. “Using either function lets you quickly return the boom to these exact positions whenever you need. It saves time because it greatly reduces the amount of repetitive operator inputs required in load-and-carry applications.”
Keep wheels on the ground and pulling in all types of terrain
Traction in diverse terrain is another compact wheel loader strong point. Some units come equipped with limited-slip axles, which automatically provide more torque to wheels that aren’t slipping in mud or sand.
“To ensure maximum efficient drive, I recommend spec’ing a loader with 100-percent differential front and rear locking axles,” says Jarvis. “Planetary axles are best as they are stronger than conventional axles and give you maximum torque in all conditions.”
Full lockup, or 100-percent differentials also increase overall tire life on a compact wheel loader if they are used correctly, Brigman-Westphal notes, since tires are subjected to less slip when differential locks are engaged. “Differential locks are easy to use,” she adds. “On Volvo machines you engage the system by selecting a button on the loader joystick. This locks in the four wheels by engaging a dog-clutch, which then sends torque to any non-spinning wheel. The result is a fully unitized powertrain pulling together in a highly efficient manner.”
Axle articulation is another important feature of compact wheel loaders. “Some loaders have the articulation point set forward of the machine’s center,” Jarvis says. “This geometry lets the rear tires track outside of the front tires and can leave tire marks on the ground – so you should check this arrangement if you’re using the machine in landscaping and finish work.”
Jarvis says a front-articulating loader also allows the rear of the machine to swing wide in tight turns. “So there’s an increased risk of hitting trees, posts or other obstacles,” he says. “I’d recommend spec’ing a loader with center oscillation. This configuration allows the tires to stay on the ground longer in rough terrain, giving you improved traction, particularly when combined with differential-lock axles.”