Technology makes JT2720 faster, stronger, friendlier. (Ditch Witch JT2720 directional-boring machine)
Published in: Construction Equipment
Date: 2/1/1998
By: Moore, Walt
The Ditch Witch JT2720 directional-boring machine is clearly superior to its predecessor, the JT2321 model, in terms of greater down-hole horsepower, backreaming speed, increased flow at higher pressures and overall efficiency. The new model enjoys both boring and pullback advantages over the earlier model by as much as 37% and is more convenient to operate because of its automated features such as a built-in monitor and a hydraulic back-up wrench.
TEST SET
New model JT2720 Type Directional boring machine Size 3.5-5 inch bores Available Feb. 98 Replaces JT2321
New model objectives:
* Increase overall efficiency
* More thrust force
* More pullback force
* Higher mud flow
* Higher spindle speed
* Increased operator convenience
When we compared the new Ditch Witch JT2720 directional-boring machine with its predecessor, we found the technically advanced new model surprisingly more productive and easier on the operator
In CE’s June 1996 issue, a Field Test compared two Ditch Witch directional-boring machines: the 4/40A, an umbilical machine that needed a support trailer to function, and the JT920, an early self-contained model that carried, onboard, virtually everything needed to make a bore. The JT920 proved 55 percent more productive in that test. Now, self-contained machines have become basically the standard of the industry, and technical refinements continue to evolve. CE editors recently got a close look at what this evolving technology means at the jobsite, when we again compared two Ditch Witch models in a Field Test.
In mid-November last year, the Charles Machine Works, maker of Ditch Witch products, arranged for an on-site comparison of its new JT2720 Jet Trac directional-boring machine with the new model’s predecessor, the JT2321. Keep in mind that when the self-contained JT2321 was introduced in July 1996, just 20 months ago, it was considered a state-of-the-art machine. But in that short span of time, the evolving application of technology has allowed even more advanced models to emerge.
The new JT2720, in fact, says Kelvin Self, Ph.D., design team manager, represents more than just technical refinement in the Ditch Witch Jet Trac line. The new model, he says, embodies what may be called a new – or more mature – philosophy of directional boring. It’s an approach, he says, aimed at making a machine more efficient, overall, by combining a number of elements that support that goal – including higher spindle speed, more spindle torque, increased fluid-flow rates, automation, refined down-hole tools, and drill pipe that’s straighter, stronger, and more resistant to torsional windup.
Although you’ll later see in detail how the JT2720 and JT2321 compared during the test, the overall result was an average production advantage approaching 37 percent for the new model. Plus, the new model carried considerably more pipe onboard (520 feet vs. the JT2321’s 320 feet), and it used a simpler, less expensive drilling-fluid (mud) delivery system that reduced its overall on-site cost, compared to that of the JT2321.
Test details
The November 18th comparison of the JT2720 and JT2321 was conducted in a large open field (the site of former oil wells) near Perry, Okla., home of the Charles Machine Works. Except for a single water line that ran across the property, we were assured by the owner that no other buried utilities were in the area. The soil at the test site was typical Oklahoma red clay, relatively free of rock. The weather was dry and unusually warm, with afternoon temperatures touching 65F.
The mechanics of the Field Test were designed to simulate a typical directional-boring job. The test started with the machines and all supplies loaded on trucks and trailers, just as they would arrive at a jobsite. Our test crews were asked to unload the machines, move them to the worksite, ready them for work, make an approximate 250-foot bore with a 4-inch bit (at a 5-foot depth), pull in a 10.5-inch backreamer, then pack up the machines and supplies ready to leave the site.
To get the best picture of how technology and the rethinking of directional-boring fundamentals have affected production capability, we used the JT2321 with the pipe and down-hole tools considered most advanced when the machine was introduced. This meant using standard Fluid-Miser pipe, a compact fluted-cone backreamer, and a Subsite 84 beacon – all Ditch Witch products.
The JT2720, however, used Ditch Witch pipe and down-hole tools developed since the JT2321’s introduction: specifically, a just-released, new type of pipe (Power-Pipe); the new Beavertail backreamer; and a Subsite 86 beacon, which provides stronger signals, quicker updates, and more stable sensors than its Subsite-84 predecessor.
Both beacon housings were equipped with the Ditch Witch Beacon-Buddy, a temperature-sensitive alloy screw plug positioned just behind the bit. If the nozzle in the bit clogs, stopping fluid flow through the housing and causing the housing to heat up, the plug will melt at a specified temperature, thereby allowing fluid flow past the beacon to be restored and preserving it from burning up – which is how many beacon failures occur.
The bore path of both machines was traced with a Ditch Witch Subsite tracking receiver, the receivers being essentially identical. Each machine also was equipped with a Subsite 90D receiver monitor. Down-hole tools for both machines were secured via the EZ-Connect system, which uses a sliding octagonal collar (positioned by an allen-head screw) to lock the tool to the drill string.
Both machines were supplied with drilling fluid (a water/detergent mixture) from large off-board tanks carried on their transport trailers. The JT2720, with an on-board mud pump capable of producing flows up to 47-gpm, was supplied with drilling fluid from its trailer-mounted mud-mixer system. This system simply moved fluid from the storage tanks to the JT2720’s on-board mud pump, which itself created the high-pressure flow needed for boring and backreaming.
The JT2321, however, was supplied with fluid from a Ditch Witch PP35T Power Pac. The Power Pac is a trailer-mounted engine/mud-mixer/high-pressure-pump combination that supplies pressurized (up to 1,500 psi) fluid flow at rates up to 22 gpm directly to a machine’s drill string. Thus, the JT2321’s 19-gpm, on-board mud pump was bypassed. Using the PP35T Power Pac with the JT2321 is typical in soils and bore lengths such as those involved in the test, says product manager Richard Levings, and has the net effect of adding about 20 hp to the JT2321.
Two crews were involved in the comparison. Each crew operated both the JT2720 and the JT2321 through a complete test cycle, that is, setup/bore/backream/and pack-up. John Skinner, test technician, and Jeff Goldsberry, factory representative, were the Charles Machine Works crew; Shane Citrowske and Wayne Steffen were the contractor crew. Citrowske and Steffen, both with nearly 10 years of directional-boring experience, are co-owners of SWI Underground, headquartered in Edwardsville, Ill.
On site for the test from the Ditch Witch factory were Richard Levings; David Bazzell, product planning manager; Brad Finley, down-hole tools manager; and Audrey Branson, public relations coordinator.
Technical advances
Explaining the JT2720’s impressive gains in productivity over its JT2321 predecessor during the Field Test involves more than just looking at the technical advances of the new machine itself. Also to be considered is the technology embodied in the pipe and backreamer it used.
First the basics: the JT2720 has considerably more gross engine horsepower than the JT2321 (125 vs. 79); spindle torque at stall is double for the JT2720 (2,700 pound-feet vs. 1,300); spindle speed (loaded) is 18 percent higher for the JT2720 (195 rpm vs. 165); actual thrust is up by nearly 59 percent for the new model (27,000 pounds vs. 17,000); and pullback is up 35 percent (27,000 pounds vs. 20,000).
Overall, the JT2720 is a stronger machine that generates more down-hole horsepower – essentially the product of torque and rotational speed, says Self, with the efficiency of the hydraulic system added in. And, the JT2720’s hydraulic system is all new, with two variable-displacement pumps, one for rotation and the other for thrust, pullback, and mud. A small fixed-flow pump powers miscellaneous functions. The JT2321, by contrast, uses three fixed-flow pumps: one for thrust/pullback; one for rotation; and the third for the mud pump.
“The JT2720’s new hydraulic scheme,” says Self, “allows the horsepower to shift to the desired function in order to maximize the machine’s operating point – no matter what the conditions. For example, if you want to consume close to 100 percent of the machine’s power for spindle rotation, you have enough pump to do that. Or if you want to run at an efficient rotation, but also use a fair amount of horsepower at the mud pump, you have that flexibility.”
Essentially, the new variable-flow pumps deliver more flow at higher pressures to produce more hydraulic horsepower. If this added power is used, as Self noted, to increase the JT2720’s spindle-rotation speed and productivity, then it follows, he says, that the machine needs a higher rate of drilling-fluid flow to mix – or fluidize – the greater volume of spoil created. The JT2720 was given that capability with its big 47-gpm mud pump.
Faster pullbacks
Extending this high-speed/high-flow concept to backreaming, says Self, was prompted by Ditch Witch engineers when looking for alternatives to developing even larger, heavier down-hole tools that could absorb more torque. It was determined that lighter tools, rotating faster, would accomplish the same goal. But to capitalize on this design, an increased fluid-flow rate would be needed to process the greater volume of spoil created per unit of time.
What emerged from this rethinking of down-hole tools was the new Beavertail backreamer. The Beavertail, according to Self, moves quickly through the bore; and its high rotational speed rapidly mixes large amounts of spoil and drilling fluid to form a slurry. Complementing this capability is its ability to let large volumes of this slurry pass behind it for lubricating the product being drawn in.
The JT2720’s backreaming speed is further increased by its high carriage speed (150 fpm vs. the JT2321’s 95 fpm). The operator can push a button on the single-lever, thrust/rotation joystick to switch hydraulic flow through the machine’s two thrust motors from a parallel to a series mode. In the series mode, each motor, in turn, receives full hydraulic flow, which serves to increase carriage-return speed. The other side of this feature is that the two motors, in their parallel-flow mode, generate more thrust at the carriage chain than does the single thrust motor of the JT2321.
In fact, says Self, increased thrust capability of newer models, such as the JT2720, has pushed the development of the new Ditch Witch Power-Pipe. Standard Ditch Witch pipe, he says, is made from pipe lengths that have been “upset-forged” by heating the ends of the pipe red hot, then applying pressure to thicken the pipe wall at the ends for threading.
Basic Specifications Comparison
JT2321 JT2720
Engine make/model Deere 3029T Deere 4045T
Horsepower (gross) 79 125
spindle speed (loaded) 165 rpm 195 rpm
spindle torque (stall) 1,300 foot-pounds 2,700 foot-pounds
Thrust (actual) 17,000 pounds 27,000 pounds
Pullback (actual) 20,000 pounds 27,000 pounds
Carriage speed 95 fpm 15 fpm
Bore diameter range (inches) 3-5 3.5-5
* List price $185,000 $180,000
* CE estimates for units as tested
“The problem is that the upset-forging process bends the pipe, which then has to be straightened,” says Brad Finley, down-hole tools manager. “But since Power-Pipe isn’t subjected to the heat and pounding of upset forging (it’s welded), it starts life straight and remains so.”
Easing the operator’s task
The JT2720’s “mobiling” system uses a tethered ground-drive control. With this control, the operator can stand well away from the machine when positioning it for work or when moving it onto the transport trailer. The tethered controller also gives the operator the freedom to walk around the machine to check its progress during these maneuvers. The JT2321 operator rides on the machine when mobiling; nothing wrong with this arrangement, but the JT2720’s remote control does allow the operator to get a better view of the travel path.
Once in position, the two machines can be anchored with equal speed and ease. Both use an anchoring system with integral hydraulics for augering in the stakes, but the JT2720’s system is more flexible. The JT2321 has two fixed anchors, and if they should be positioned over a rock or other obstacle and can’t be drilled in, then the machine must be repositioned. The JT2720’s system, however, can use up to four anchors, which can be pivoted for avoiding obstacles without moving the machine.
To further simplify setup, the JT2720 has a double-pivot mechanism that eliminates having to slide the drill frame back and forth to change the drill-string’s entry angle, as is the case with the JT2321. The new system allows settings that range from 10 to 23 degrees, while it keeps the overall length of the machine constant and the tracks squarely on the ground.
Sit in the operator’s seat of the new model, and you’ll notice several changes, compared to the JT2321. Most prominent is the JT2720’s single-lever thrust/rotation controller, compared to the JT2321’s two-lever design. According to Levings, the majority of buyers want single-lever control, but admits that the joystick system does require some practice to master.
One feature the JT2321 uses, but the JT2720 has dropped, is the Ditch Witch Automatic Bore Control system. This system automatically adjusts thrust/pullback forces and rotation speed to match conditions. The JT2720’s joystick, however, does have travel stops that can be adjusted to set thrust and rotation at limits preferred by the operator.
Another control difference is that for pipe-handling. While the JT2321 has a hydraulic pipe-handling system, the operator must use switches to activate the shuttle-arm and storage functions, as well as the mud pump’s operation. On the JT2720, however, these functions are given over to microprocessor control. A carriage-position sensor determines when the pipe-handler should be activated, and sensors at the wrenches turn the mud pump off and on automatically. If the operator prefers to control these functions manually, an over-ride switch is provided.
Also for the convenience of the JT2720 operator is a built-in monitor for the optional, on-board, Subsite 90D tracking receiver. Tucked neatly into the control panel, the monitor provides the same information as the field receiver. While a remote receiver was also available for the JT2321, it was packaged as a portable unit and not easily accommodated in the operator’s station.
The JT2720’s operator-convenience features further include a hydraulic back-up wrench, which relieves the operator of having to manually fit a wrench to the drill string to assure that the first pullback joint breaks in proper sequence.
Summing up
Reflecting on the JT2720 vs. JT2321 Field Test, we were impressed by the new model’s productivity gains, but also had the feeling that we were observing more than just a comparison between two specific machines. That something more, we think, was what design team manager Kelvin Self had described as a maturing approach to design in Ditch Witch directional-boring systems, an approach likely to characterize the further development of the company’s systems.
Specifically, product development efforts seem clearly focused on self-contained models, even though big umbilicals remain in the line for jobs requiring compact machines with plenty of power. And we’d guess that these future self-contained models, assuming the JT2720 is representative of things to come, will progressively embrace more automation, increased down-hole horsepower, higher mud-flow rates, greater thrust and pullback forces, and modified pipe and downhole tools that capitalize on these enhancements.
JT2720 Boring Advantage
37% …or an additional 3.5 feet/minute
JT2720 Pullback Advantage
36% …or an additional 2.4 feet/minute
RELATED ARTICLE: DUTCH WITCH JT2720 DIRECTIONAL BORING MACHINE
JT2720’s Design Results in Greater Productivity
The figures in the accompanying table are averages calculated from the performance of both crews. Note that the production advantages for the JT2720 when boring and when backreaming are nearly identical. Set-up and pack-up times are essentially equal between the two models.
Performance Comparison
JT2321 JT2720
Bore (feet/minute) 9.4 12.9
Production advantage – 37.2%
Pullback (feet/minute) 6.6 9.0
Production advantage – 36.4%
Set-up time (minutes) 8.9 8.7
Pack-up time (minutes) 6.5 6.7
The “Technical Advances” section of this report gives the details of the JT2720’s design that likely result in its impressive production gains, compared to its predecessor. To summarize here, however, credit the new model’s advantage to its greater down-hole horsepower, its higher fluid-flow rate (up to 47 gpm), its increased thrust and pullback forces, and its use of stiffer pipe and the new low-resistance backreamer.
Performance Comparison
JT2321 JT2720
Bore (feet/minute) 9.4 12.9
Production advantage – 37.2%
Pullback (feet/minute) 6.6 9.0
Production advantage – 36.4%
Set-up time (minutes) 8.9 8.7
Pack-up time (minutes) 6.5 6.7
COPYRIGHT 1998 Reed Business Information