Mention tool carrier and a number of machines come to mind, including the wheel loader, skid-steer loader, hydraulic excavator and backhoe-loader. Seldom, however, do we use the term for wheel-mounted, chain-type, ride-on trenchers — even though these machines are among the most versatile around.
Although the definition of the machines in this Buying File is a mouthful, the term "wheel-mounted" (rubber-tired) separates them from crawler-mounted chain-type trenchers; "chain-type" separates them from wheel-mounted trenchers that use only a wheel-type trenching device; and "ride-on" separates them from pedestrian (walk-behind) models. Could we agree just to call them "ride-on trenchers" from here out?
Just to set the record straight, calling a ride-on trencher a "tool carrier" isn't meant to imply that users of these machines are switching attachments as frequently as users of skid-steer loaders would. Most of these machines, in fact, spend their days as dedicated trenchers. The point is, though, that most models in this equipment category have the potential to transform themselves into different machines — all competent excavators — as applications vary.
For example, the user might on occasion swap the trencher attachment for a rockwheel (akin to a big circular saw) to make neat cuts across asphalt and concrete roadway that lie in the trencher's path. Or, if users select a "combo" (a combination trencher/plow), they might choose to install utilities with the plow in warm weather, then with the trencher when frost hardens the ground. In either instance, a front-mounted backhoe would be handy for digging access holes at the ends of the trench.
Of course, some machines fit the so-called "Swiss Army Knife" concept right from the factory, being equipped with a trencher (or plow), backhoe, backfill blade and a small, hydraulically powered, horizontal-boring unit for punching under sidewalks and driveways. A combo would add yet another dimension of utility to machines so configured.
On the other hand, some of these machines spend their days working in solid rock formations and, thus, are used only with a rockwheel. Others might serve as dedicated plows, and may be fitted with a heavy-duty reel carrier to simplify handling cable and flexible gas line. So, although the ride-on trencher may not be a quick-change attachment swapper like a skid-steer loader, it does remain a rugged, capable prime mover that does many jobs well.
For your information, recent changes in the manufacturing community for ride-on trenchers include the exit of Burkeen and Parsons from the market, although Parsons (part of Maxon Industries) continues to sell two dedicated vibratory plow models, the D-60 and D-100, rated at 82 and 110 net horsepower, respectively. Also, the acquisition by Astec Underground (an Astec Industries company) of the former Case range of ride-on trenchers was completed late last year.
The ride-on trencher is equipped with two basic drive systems, the ground-drive system, which propels the machine around the jobsite and provides controlled forward motion when trenching; and the chain-drive system, which powers the trencher chain. In the past 10 years or so, the design of these systems has shifted increasingly from mechanical to hydrostatic.
In a hydrostatic system, typically, a variable-displacement hydraulic pump supplies fluid flow to a hydraulic motor in a closed-loop, that is, fluid exhausting from the motor is essentially all channeled back to the pump. The motor, which converts fluid flow to mechanical motion, usually (but not always) drives through a gear set to increase torque in the ground-drive and trencher-drive systems. (The motor drives a multi-speed powershift transmission in some instances.) A purely mechanical-drive system, by contrast, typically uses a mechanical transmission, clutch and a series of shafts, chains, belts and pulleys to power the drive wheels and chain.
In the February 1994 issue, a Construction Equipment Field Test compared Vermeer's mechanical-drive V-430A to its then-new hydrostatic-drive V-4150. Two big hydraulic pumps, coupled to the V-4150's engine, powered two motors, one driving through a gearbox to the axles, the other directly driving the trencher chain. At the time, some in the industry assumed that, although the hydrostatic system was simpler in design and more operator friendly, it couldn't deliver as much engine power to the trencher chain or drive wheels as could a mechanical system. As it turned out, the CE test found a 28 percent production advantage for the hydrostatic machine.
Opinions about ground-drive and chain-drive drive systems, however, still vary. Although most ride-on trenchers available in today's market are completely hydrostatic, as are Vermeer models and the Hydramaxx HM2500, a few reflect an alternate design. In the Astec line, for example, all models use hydrostatic ground drive, and all but the model 360 use hydrostatic trencher drive. The 32-hp (gross) 360 uses a mechanical trencher drive incorporating an over-center clutch.
In the Ditch Witch ride-on range, all models are completely hydrostatic, except the model RT36 and a variation of the RT75 and RT95. The RT36 is a completely mechanical machine, both ground drive and trencher drive. This model, says senior product manager, Brent Bolay, is a dedicated trencher and can be used with no other rear digging attachments. It can, however, be fitted with a backhoe and Ditch Witch's Roto-Witch boring unit.
The Ditch Witch RT75 and RT95 are available in a completely hydrostatic configuration, or in a "powershift" configuration, which, as the name implies, employs a powershift transmission that is driven in conventional fashion via a torque converter off the engine. The machine maneuvers around the jobsite using its powershift drive train, but when trenching begins, the powershift drive train powers the trencher chain. Ground drive during trenching is handled by a hydraulic (not hydrostatic) system that uses a gear-pump and hydraulic motor arrangement to power the axles. The powershift models are available only as dedicated trenchers and are used primarily in high-production applications.
If you're thinking about buying a trencher/plow combination for a new machine, note that manufacturers agree that the performance of one or the other tools will be somewhat compromised, because both are operating in an offset position. But which tool? One opinion says the trencher's performance is most affected, especially when pulling off-center through difficult or frozen material. The other opinion says, "geometry is everything when plowing" and, thus, plow performance is most affected in the off-center position. It's a discussion to have with your dealer. If you need both tools, most do agree that the combo makes more sense than buying separate tools and switching between them.
Another item that a knowledgeable dealer salesman needs to discuss with you is the design of the trencher chain, specifically boom-style, basic chain design and teeth.
Trencher booms (the backbone of the trencher attachment) normally are available in two basic styles — "rock" and "dirt." Typically, the dirt boom has a more open design that allows the trencher chain to more easily shed wet or sticky material. The rock boom, usually, has a more solid (and robust) design with a large-diameter end roller (not a sprocket) to keep rocks from catching in the chain, causing added wear. If soil conditions allow, most manufacturers suggest using the rock boom.
According to Astec Underground's Bob Wren, training manager, rock booms have become somewhat of an industry norm. Generally, says Wren, rock booms require less maintenance than a dirt boom, run smoother and quieter with their large tail roller and, because they are typically heavier than a dirt boom, tend to be more productive.
Selecting the specific chain and teeth for the trencher attachment is a science based on experience. Chains from a given manufacturer may be available in four or five basic styles to suit ground conditions and specific performance requirements, and chain-and-teeth assemblies may number 10 or more. Although the "cup" tooth is considered by most to be the "standard," teeth are available in various styles to suit material conditions, and may be combined on the chain in a specific pattern to yield the best blend of performance and durability.
Although chains with bolt-on (vs. welded) teeth can be fitted with spacers to increase the chain's cutting width within practical limits, most of the time a chain is built and used to yield the cutting width most often required in the material most often encountered. In those situations where the machine is used over a wide geographical area with a known variation in soils, says Vermeer's Todd Roorda, the user may be best off buying more than one chain. It's easier to switch the entire chain, he says, than to swap all the cutters.
|Wheel-Mounted, Chain-Type, Ride-On Trenchers|
|Model||Operating Weight (lb.)*||Max. Trench Depth (in.)||Trench Width Range (in.)||HP (net)|
|* With standard trencher attachment|
|** Tractor-only weights|
|*** Tractor-only with counterweight and backfill blade|
|Astec ( www.astecunderground.com )|
|Ditch Witch ** ( www.ditchwitch.com )|
|Port Industries ( www.portindustries.com )|
|Vermeer ( www.vermeer.com )|