Performance Factors. A number of features and specifications can be used to gauge the productivity of a particular model. But keep focused on why you want a compact excavator, suggests Keith Rohrbacker, product manager with Kubota Tractor Corporation. "No machine offers you the most of everything. Somewhere along the line you have to make tradeoffs, like between a machine that will give you the highest production and one that will fit into your work spaces. Remember why you're buying the machine and beware of the tendency to buy more than you really need. At the same time, keep your future plans in mind so that your excavator can continue to meet your needs as your work changes. A compact excavator can easily last you five to seven years."
Engine Power :
Higher engine horsepower ratings don't equate to increased performance when it comes to compact excavators. Depending on how a machine is engineered, one model, which uses available horsepower more efficiently, can outperform another model with a larger engine. Also, since there are no transmissions or driveshafts, the engine on a compact excavator powers only hydraulic motors. So it's more important that the engine is matched properly to the hydraulic pumps. "Otherwise you could overload an engine, resulting in increased fuel consumption and overheating," says Rohrbacker. "That, in turn, can increase operating and maintenance costs."
Also, keep in mind that most construction equipment, including compact excavators, operate most efficiently within a certain performance envelope. "A diesel engine operates most effectively when its running at about 80% to 90% of its maximum capability," Rohrbacker notes.
"Many people like big machines with lots of power," adds Harry Lao, president of Pine Brook Construction Equipment, Inc., which manufacturers miniexcavators. "That could be a costly mistake with compact excavators. You need to look at the intended use of the machine. The price difference among the different sizes of miniexcavators can be quite significant."
Digging Depth
Regardless of size, any compactor excavator is at its peak effectiveness when most of the digging is no deeper than about 60% of the machine's maximum digging depth, Rohrbacker notes. That represents a good balance between time spent digging productively and time spent repositioning the machine. "That's where most of the machine's strength and speed is," he says.
The rated maximum digging depth is designed to provide a 2-ft. length of flat bottom when digging a trench. To dig more flat bottom, you have to move the excavator.
Consequently, using an excavator capable of digging 10 ft. deep to dig a 6-ft.-deep trench will allow you to dig about 8 ft. of flat trench bottom before you need to reposition.
Digging Power
One measure of an excavator's productivity is arm or crowd force: the machine's ability to produce a pulling force using the hydraulic force of the arm or dipper. Bucket breakout force measures the prying force of the machine using the bucket hydraulic circuit. The higher the breakout force for the bucket and dipper, of course, the easier and faster the digging. However, Rohrbacker suggests viewing these ratings in perspective. "A high bucket breakout force should not be your primary selection criterion," he says. "When you're trenching, you're using not just the bucket but also the arm and boom. A higher breakout force is much more important if you are digging in tough, hard ground than in softer conditions."
Cycle Time
Productivity of a compact excavator also depends on how fast it works: how long it takes to fill the bucket with dirt, over to dump it, swing back to the dig area, and start the next cut with the bucket. This reflects both the amount of hydraulic flow produced by the pumps, how it's directed by the valves to the cylinders, and how quickly and smoothly the cylinders retract or extend. The fastest machines allow you to swing the house, curl the bucket, extend the arm, and raise the boom all at the same time.
Type of Hydraulic Pump
In the past, all the pumps on most compact excavators were gear-type. This pump uses rotating gear assemblies within a pump housing to produce the hydraulic oil flow. In this case, engine speed determines hydraulic flow. In addition to costing less to produce, tolerances on a gear pump aren't so critical, so it tolerates some contamination in the hydraulic oil better than the piston pumps found in big excavators.
In the past few years, however, more and more compact excavator manufacturers have been adopting the piston pumps, also called variable displacement pumps, at least for their larger models. Piston pumps feature more expensive technology, which provides variable hydraulic flow and better pressure control. This pump produces oil flow using a rotating assembly of small pistons, which controls the oil flow independently of engine rpm and pump shaft speed. The end result is a more efficient, smoother operating system.
Digging Power
One measure of an excavator's productivity is arm or crowd force: the machine's ability to produce a pulling force using the hydraulic force of the arm or dipper. Bucket breakout force measures the prying force of the machine using the bucket hydraulic circuit. The higher the breakout force for the bucket and dipper, of course, the easier and faster the digging. However, Rohrbacker suggests viewing these ratings in perspective. "A high bucket breakout force should not be your primary selection criterion," he says. "When you're trenching, you're using not just the bucket but also the arm and boom. A higher breakout force is much more important if you are digging in tough, hard ground than in softer conditions."
Cycle Time
Productivity of a compact excavator also depends on how fast it works: how long it takes to fill the bucket with dirt, over to dump it, swing back to the dig area, and start the next cut with the bucket. This reflects both the amount of hydraulic flow produced by the pumps, how it's directed by the valves to the cylinders, and how quickly and smoothly the cylinders retract or extend. The fastest machines allow you to swing the house, curl the bucket, extend the arm, and raise the boom all at the same time.
Type of Hydraulic Pump
In the past, all the pumps on most compact excavators were gear-type. This pump uses rotating gear assemblies within a pump housing to produce the hydraulic oil flow. In this case, engine speed determines hydraulic flow. In addition to costing less to produce, tolerances on a gear pump aren't so critical, so it tolerates some contamination in the hydraulic oil better than the piston pumps found in big excavators.
In the past few years, however, more and more compact excavator manufacturers have been adopting the piston pumps, also called variable displacement pumps, at least for their larger models. Piston pumps feature more expensive technology, which provides variable hydraulic flow and better pressure control. This pump produces oil flow using a rotating assembly of small pistons, which controls the oil flow independently of engine rpm and pump shaft speed. The end result is a more efficient, smoother operating system.
"A variable displacement pump gives you a very good feel for the machine," says Lao. "You can tell the difference between these pumps and gear pumps immediately."
Rohbacker notes another advantage. "The variable displacement or piston pump automatically switches between low flow for power when you're digging and high flow for speed using other functions. That reduces cycle times and lets you get the job done faster."
ives you a very good feel for the machine," says Lao. "You can tell the difference between these pumps and gear pumps immediately."
Rohbacker notes another advantage. "The variable displacement or piston pump automatically switches between low flow for power when you're digging and high flow for speed using other functions. That reduces cycle times and lets you get the job done faster."
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