Chain-type trenchers — 76 to <100 horsepower

|  June 12, 2007 |

Timely installation of utility lines places an emphasis on quick, accurate trench excavation, utility placement and spoil replacement. Chain-type trenchers in the 76 to <100 horsepower class fit this job description perfectly. These are self-contained, high-production trenching machines – often outfitted with a backhoe attachment – designed to quickly excavate trenches 3 to 5 feet deep and 8 to 16 inches wide. Primary applications are utility trenching work including water, telecommunications and natural gas lines.

According to Brent Bolay, senior product manager, Ditch Witch, one of the most important attributes for trenchers in this horsepower class is their physical size. "These trenchers are well suited for applications in urban areas," he observes. "Smaller walk-behind trenchers can't handle the increased trench depths and widths and longer runs these models can. Larger trenchers can complete longer runs in less time. But they tend to be more awkward in tight work environments and are generally less maneuverable."

"Generally, more options are available on trenchers in this size class," says Brian Kenkel, product manager, Vermeer. "That makes them easy to match to specific jobs or types of work. Contractors have the ability to spec these trenchers for everything from broad trenching applications all the way down to niche applications. That's a role smaller and larger trenchers can't fill as effectively."

Backhoes are a popular attachment for trenchers in this class, and one that makes a lot of sense for most contractors, according to George Whitaker, marketing director, Case Construction Equipment. "A backhoe gives your trencher increased versatility and efficiency," he notes. "In many cases, a backhoe means one less machine on a given jobsite, or it can free up a backhoe loader or compact excavator to perform other, higher-volume jobsite tasks."

Whitaker says many contractors, whether plowing in cable or open trenching to install conduit, find themselves having to cross driveways or roads. In those instances, a backhoe can be used to dig exit and entry pits for various types of boring attachments. "It also gives you the option of high-precision excavating," he adds, "which a trencher alone cannot do."

Soil can make or break your trenching production. Carefully spec teeth for your chain and check it often once it’s in use.

Look to powertrains when spec’ing your excavation model
Spec’ing a trencher in the 76 to <100 horsepower class is fairly easy, but there are different machine configurations and powertrain combinations you should bear in mind.

While this article focuses on chain-type trenching machines, remember that you can also spec a saw-type trenching boom for machines in this class. "That decision is based strictly on application," says Whitaker. "If you're working in material that tends to fracture or chip, you're better off selecting a trencher equipped with a rock boom using welded H-plate or alligator-type chain designed for rock and hard compacted conditions." If you're working in soil that requires more of a grinding action to penetrate, then Whitaker says the combination of additional weight and consistent surface contact of a rocksaw will make it a more productive choice. "Bear in mind, though," Whitaker cautions, "that depending on application, rock wheels can cost up to 20 percent higher compared to a chain-equipped model."

Powertrain types can dramatically affect trencher performance and deserve careful consideration during the spec'ing process. There are two common powertrain types found on trenchers in this class: powershift and hydrostatic drives.

Powershift transmissions feature a torque converter drive to the trencher. In Ditch Witch's model lineup, Bolay says powershift machines are the true high production trenchers. "To a certain extent, they're dedicated trenching machines," he explains. "That's because you get the most productivity for the available horsepower produced by the engine. A powershift trencher uses the engine's gross horsepower more efficiently – and transfers more power to the digging chain than any other drive we've ever tested." That doesn't mean that hydrostat trenchers are shrinking daisies by any means. "Hydrostatic drive systems are extremely reliable," Bolay adds. "And from a control standpoint they're very easy to operate." But their real benefit, he says, is the additional flexibility they offer contractors beyond conventional trenching applications.

That's because hydrostatic drive systems are extremely adaptable. So while hydrostat trenchers are highly productive in straightforward trenching applications, contractors also have the option of using hydraulically powered attachments on the rear of the machine beyond a backhoe. "For starters," Bolay says, "you can opt for a traversing boom that moves from the centerline of the tractor to an offset position to the right, or a vibratory plow with a steerable plow blade. Those attachments aren't nearly as easy to engineer with a mechanical drive system."

To the untrained eye, Bolay says many powershift and hydrostat trenchers appear identical. But each type has its place in a contractor's excavating arsenal. In general, spec powershift trenchers for aggressive, around-the-clock trenching work in harder soils. If you're planning to use the machine in a more flexible role, then a hydrostat machine will be a better production match.

Spec chain for productive trenching
To be effective, your trencher must have the correct type of chain on its boom. This isn’t as easy as it sounds. Ground conditions dictate the chain type used and these can change rapidly from one jobsite to another, or even during the course of a single trenching run.

All manufacturers say your local dealer is really your best source when it comes to optimizing chain productivity on your trencher. They’re extremely knowledgeable about soil types in their sales area and can recommend a chain configuration to meet the specific conditions you’re dealing with.

To be effective, make sure your trencher is spec’d with the proper type of chain for the ground conditions you’re working in.

“There’s an upfront cost to any trencher chain, and you need to factor that cost against the number of hours you’re going to get out of it,” Kenkel says. “Vermeer offers a variety of chains for trenchers in this class – but you have to use the right chain in the right conditions to maximize the hours you’ll get from it. Our lower cost chains can last as long as any other chain in our inventory if they’re used in the right conditions.”

The key, Kenkel says, is to consult your dealer and learn all the chain options available. “We understand chain life and productivity are major concerns for contractors running trenchers,” he says. “And regardless of soil types there are almost always solutions available – and we try to maximize chain life in even the harshest ground conditions.”

As an example, Kenkel points to Vermeer’s patented Super Duty chain. “There is no thimble or roller on this chain – it’s all one piece,” he explains. “In really hard ground conditions,
the lack of moving parts lends to added strength and increased chain life. Because the feed roller is fixed, there is four times the material to wear on the contact patch with the sprocket compared to conventional digging chains. As you experience extreme wear on one side of the fixed roller, simply turn the chain and sprocket around and continue trenching. This will extend chain life if managed properly.”

Soil is what makes or breaks a trenching operation, according to Bolay. “There are times,” he notes, “when you’re better off switching to a rock saw attachment in extremely harsh conditions.” But, he cautions, chains are optimized for different types of soil, so simply spec’ing carbide shark teeth isn’t a viable answer.

“I’ve seen contractors who decided to put the most aggressive cutting teeth available on their chains and assume they were good to go in all types of soil,” he says. “But you’re not. Carbide teeth are an excellent choice in rocky soil, but a terrible choice in soft, loamy ground. That’s because carbide teeth are designed to cut, not scoop. Spec them in soft dirt, and you’ll end up with a trencher that’s blending soil instead of excavating it. You end up losing productivity and running your machine harder, but accomplishing less with it.”

Even if you’re certain you’ve spec’d the proper chain for the job at hand, remember ground conditions change rapidly. So your operators need to monitor the trencher’s chain – checking it at least once a day to see how the teeth are holding up. “A routine inspection is all you need to do,” Bolay says. “Mainly you want to see how the chain is wearing. Look for unusual wear patterns and track deterioration on the digging teeth. If your productivity starts to fall off, check that against tooth wear. If you decide you need to change teeth, change them out in a complete set rather than spot-changing a piece or two. Replacing one tooth gives the chain a completely different cutting pattern because you have a new tooth with a higher profile from the worn teeth. You end up making the new tooth work harder, while the partially worn out teeth don’t produce like they should.”

Find the sweet spot for maintaining daily production
Once the boom is in the ground and cutting earth, chain speed becomes a huge productivity factor. Kenkel says you can have two machines identically set up with the same cutter pattern on the chain, and the one running chain too fast will actually cost you footage when compared to the other machine running at the proper speed. “On the other hand,” he adds, “running a chain too slow may also cost you footage. So you’ve got to strike a balance.”

Kenkel says there’s a good, practical method for determining what footage rate is the most productive and cost effective for your trencher. Set up the trencher and put your plunge cut in the ground. Get the trencher up to speed and then slowly reduce the chain speed down until it starts to hurt your productivity. “Now,” Kenkel says, “adjust the chain speed back up to where you were just before production began to fall off. That’s the sweet spot for cutting most effectively. You should now be getting the same amount of work done that you were cutting at those higher rpms, but you’re doing it while inflicting less wear on the trencher.”

Once you’ve hit that sweet spot, stay with it. “Slow and steady is always the best way to trench,” Kenkel stresses. “A lot of operators will keep pushing the creep lever in softer ground. What happens is they get to a speed they can maintain until they hit a hard patch of ground and the trencher stalls out. We have auto-creep functions on Vermeer trenchers that automatically stop the tires when the chain hits harder ground until the engine catches back up to optimum trenching speed. But you’ll get more footage by working at an optimum trenching speed you can maintain regardless of changing ground conditions.”

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