Wheel loaders: 150 to <175 net horsepower
| June 12, 2007 |
Wheel loaders in the 150 to <175 net horsepower class are solidly in the "bell curve," of popular machines, often selected by contractors who want a little bit more in terms of power and size from these versatile machines. "The most popular class of wheel loaders are machines in the 135 to <150 net horsepower class," notes Dan Snedecor, product manager, Volvo Construction Equipment. "But these wheel loaders – while not really intended for a true high-production environment like dedicated truck-load – are terrific for contractors who deal with heavy pipe or commonly lift materials in a utility role. That's why machines in this class still account for 20 percent of all wheel loaders sold in North America."
Wheel loaders excel at any number of construction applications, either as a material handling, digging or load-and-carry machine. Because they're so effective in a wide array of roles, they are mainstays for contractors engaged in utility and general construction applications. They are also commonly used in road building and site prep applications.
wheel loader or tool carrier?
Any discussion of wheel loaders up to 375 net horsepower would be incomplete without an examination of, and comparison to, tool carrier models. To the uninitiated, the two machine types appear identical. This is understandable since OEMs commonly use the same frame and body type for each machine model. But in reality, they are two very different machine types designed to work effectively in different applications as reflected by the distinct types of loader arm geometry each employs on the front end of the machine.
Designed primarily for aggressive digging jobs, wheel loaders feature a specialized "z-bar" linkage with a single bell-crank hydraulic cylinder that maximizes breakout force at the tip of the bucket. "z-bar machines are high-production machines," explains Dave Wolf, marketing manager, Case Construction Equipment. "Because of their linkage design, they have faster cycle times than tool carriers, allowing operators to root into a pile, raise a load and dump it more efficiently."
In contrast, tool carriers are equipped with two smaller hydraulic cylinders, each mounted on opposite sides of the loader arm geometry. The focus here is on material handling. These two diametrically mounted cylinders allow operators to maintain parallel lift, keeping a load level, throughout the linkage's entire range of motion. The benefit here is precise control in pick-and-carry applications combined with better forward visibility to aid in placing those loads. A tool carrier's parallel-lift front end is usually combined with a more potent high-capacity hydraulic system that allows it to efficiently swap and use a multitude of powered attachments.
"The key to selecting the proper machine is to base the choice on application," says Dave O'Keffe, product manager, John Deere. "But remember that either machine can handle both types of work. z-bar machines can be equipped with a quick coupler and work effectively with attachments or in material handling roles, although a coupler extends the loader geometry and cuts into the machine's potential breakout force. Conversely, tool carriers can be fitted with a bucket and can handle digging applications – although they don't have the higher breakout forces a wheel loader does."
"The point for customers to remember," adds Bob Post, product manager, Komatsu, "is that they only need a tool carrier with parallel lift if parallel lift is required in the majority of their applications and the majority of the actual working time. If parallel lift is not needed very often, the customer may be more satisfied with a more powerful digging z-bar loader."
Although parallel lift and z-bar linkages are the norm throughout the industry, there is a third type – exclusive to Volvo wheel loaders – as well. This proprietary front end geometry, called torque parallel linkage, which Snedecor says is a hybrid design that takes the best attributes of z-bar and parallel lift packages and combines them into one geometry. "Torque parallel lift offers high breakout forces and level life through the loaders range of motion," he explains. "It also has excellent visibility forward and can be fitted with our proprietary bracket to handle a wide array of attachments."
Brian Argo, marketing manager, Caterpillar, looks into the future and sees a time when modern electronic systems remove any differences between the two machine types completely. "Electro-hydraulic controls are going to evolve to the point where you'll get parallel-lift capability on a z-bar machine," he says. "A tool carrier maintains parallel-lift purely by the mechanics of the design. But electro-hydraulic controls will allow operators to turn a parallel lift function on or off as needed and duplicate that action by having the machine's ECM carefully control hydraulic flow to the bell crank cylinder."
Benchmark your production to determine optimum machine use
Making sure a wheel loader is productive for you on a daily basis means having the right sized machine for your needs, notes Gary Bell, vice president and general manager, Kawasaki Construction Machinery. “If you have a fixed production requirement like loading a plant or a crusher, make sure the loader’s production capacity matches your plant demand,” he says. “A simple production calculation can be made to determine the productivity of different sized machines. If you are not in a fixed demand application, such as grading or pipeline applications, the sizing of the loader depends on variable demands. You need to have a machine that can handle the heaviest load or highest lift required. This may mean there is some overcapacity at other times. Or you may need a smaller machine just to fit the work area if you are operating on a street or inside a building. It comes down to a judgment call as to whether capacity or cost is the controlling factor.”
Another powerful tool at your disposal is benchmarking your wheel loader’s productivity, according to Argo. Benchmarking is nothing more than tracking a loader’s productivity and comparing your results with other data. “You can obtain that information from a variety of sources,” Argo says. “Construction trade organizations or other contractors are good resources. However, your dealer is the best sounding board for determining optimum bucket sizes and styles, number of passes or footage dug in a specific time period. Historically, we have seen customers who gather good data on machine production and cost make the best equipment management decisions in the future, which ultimately leads to having a very productive job site.”
Operators – your most important production component
Like many pieces of construction equipment, the skillful handling of a wheel loader can save you thousands of dollars over the life of the machine. Likewise, a ham-fisted and inattentive operator can cost you thousands of dollars in engine, fuel, frame and tire costs over the productive life of a wheel loader.
Take, for example, the common perception that if a machine can spin its tires digging into a pile, it’s got power. Case’s Wolf says the opposite is actually true. If the loader’s wheels are spinning, he says, you’re losing tractive effort and degrading the machine’s ability to push into the pile and fill its bucket. “So you’re losing power, wasting fuel, burning up the tires prematurely and putting unnecessary strain on the frame,” he says.
Operators should also be coached to ensure they’re competent on specific wheel loader models, Snedecor says, since there can be significant performance differences among machines. Many newer wheel loaders are equipped with load-sensing hydraulic systems, which allow the operator to manipulate loads and control the boom and tilting function at low engine rpms. “More power at a lower average rpm means operators no longer have to rev the engine to move the loader arm or initiate the tilt function,” Snedecor says. “But that’s a hard habit to get operators to break. And it costs you more money in burned fuel.”
Load-sensing hydraulics don’t continuously pump hydraulic oil through the system, which Snedecor says frees up 30 to 50 horsepower when the hydraulic controls are not being used. Instead, load-sensing hydraulics reserve engine horsepower for the functions that need power the most.
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