Packing Power In Small Packages

Dec. 1, 1999
As U.S. cities age, urban infrastructure-improvement projects flourish. Working in the city is not a walk in the park, though. Construction repair and

As U.S. cities age, urban infrastructure-improvement projects flourish. Working in the city is not a walk in the park, though. Construction repair and renovation in all areas of urban utilities - water supply, drainage, electrical and gas piping - require contractors or city crews to work in constrained environments with an emphasis on efficiency.

Since most utility services are underground, the compact swing performance of hydraulic excavators has become more important than ever for contractors competing for jobs. An excavator's size, speed and versatility can make or break its profitability.

Fortunately for contractors and city dwellers, the traditional hydraulic excavator has evolved into one of the hardest-working, most versatile tools in the con struction, demolition and material-handling industries.

The standard machine, as it is commonly called, refers to most excavators now in the field. It is rugged, powerful and stable. Stability - both "static" and "dynamic" - is probably the most crucial feature of any excavator because it allows equipment manufacturers to incorporate more powerful motors and hydraulics to do more work.

To gain this much-needed stability, counterweight has been typically extended away from the centerline, opposing the bucket, to counterbalance the weight and effort exerted at the end of the boom. However, this design keeps the backside or "tail" of the excavator extended, hindering the operator's movement of the machine. When there is an obstruction, the operator has to be aware of what's behind him at all times, slowing down swing rate and productivity. The tail swing of excavators also dictates what size excavator will fit into any given space, limiting the horsepower and bucket size available to work in tight spots.

Unfortunately, the common alternative - compact or mini-excavators with small swing radius - can't match the performance of standard machines. Not only are they slower, but compact excavators can be more difficult to maintain since space within the engine compartment is so much smaller. In addition, engine noise can be much louder because the operator's cab is smaller or nonexistent.

Until recently, contractors were forced to rent their "poison" - excavators that might be too cumbersome for city jobs, or models that could fit almost anywhere but couldn't deliver the goods.

The magic pill came by way of short-radius technology - a turning point in excavator design, from the 24-ton class down to the smallest models. Now a number of excavator models, compact and larger, feature a short swing radius that keeps the back of the unit within the width of its tracks.

An invaluable product feature, "zero tail swing" has now become a mantra for rental centers and their customers, so manufacturers have dealt with the challenge of applying short-radius features to larger machines. To do so, the excavator's upper structure must be designed to swing within the width of the undercarriage and still maintain stability. At the same time, room must be found for critical engine and hydraulic-system components, taking into account maintenance.

But dynamic stability, which is measured by the subsidence of oscillation during operation, and static stability determines the true effectiveness of a short-radius excavator.

With advances in technology, each counterweight is designed to wrap the components of the engine and hydraulic system more effectively so that stability is not only achieved but enhanced. Larger cabs help improve use of the cast counterweight and compact parts arrangement for interior ergonomics equal to or better than that of larger machines.

Maintenance, including placement of the engine compartment, must also be considered.

Overall, the compact design of short-radius excavators can make them as easy to maintain as any standard excavator, and stronger, more powerful engines have improved their productivity. Short-radius technology has elevated the standards of production and performance for excavators to new heights - and depths, in the case of urban utility work.