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We've all used the wrong tool at one time or another, simply because it was within reach and it was convenient. But when it comes to excavators and backhoes, the cost of using the incorrect bucket or attachment can really add up. This is where the advantages of a quick coupler become obvious.
"Machine performance is increased with a well-designed quick-coupler system because the operator never has to work with the incorrect tool for the job at hand," says Bret Jacobson, product specialist - earthmoving excavators, Liebherr Construction Equipment Co. "He can easily change tools to suit the application."
This also has the effect of making the tools last longer, he continues. Replacement costs decrease because tools are less likely to be used for applications for which they weren't designed simply because changing tools would take too long and be too much trouble.
There are many different types and designs of quick couplers on the market, so it pays to do your homework. "When purchasing a coupler, contractors should take time to research each style available," says Tracy Black, manager, Kenco Corp. Important factors to consider include the weight; tip radius gain; ease of installation; ease of use; versatility; reliability; and maintenance requirements.
Weight impacts capacity
The weight of the quick coupler deserves your attention. "Weight is extremely important," says Black. "Each machine has a limit on the amount of weight it can lift. The heavier the coupler, the less payload you can move."
You should understand the trade-offs. "The quick coupler is a tool that allows an excavator to be used for a variety of earthmoving applications, with very little time lost changing attachments," says Kirk Yoresen, marketing communications manager, engineered products, ESCO Corp. "However, because all couplers add weight and length to the end of the machine stick, a machine digging without a coupler will have reduced performance if a coupler is added into the equation."
Weight and length added to the end of the stick can have a negative affect on the breakout performance and the Gross Allowable Lift (GAL) of the excavator, Yoresen adds. "In essence, productivity is reduced as a trade-off for increased versatility," he states.
Yet, the degree of impact the added weight may have really depends on machine size and the coupler design. "Typically, the weight of adding a coupler to your machine has limited effect on the machine performance," says Dale DeWeese, national sales manager, Werk-Brau. "However, some municipalities will add multiple attachments to the end of their machines — the combination of which could make the machine 'tippy' unless the addition of a counterweight or additional stabilizers are utilized."
The coupler's weight may actually be a benefit if you perform much lifting. "In lifting applications, such as setting pipe into a trench, a well-designed quick coupler can actually increase the performance of the machine," says Jacobson.
"Oftentimes, you will see a load hook welded to the back of a bucket. Pipe or other material will then be rigged to this load hook," he comments. But quick couplers can incorporate the hooks, enabling you to drop the bucket before lifting. "This allows the operator to utilize the resulting increase in lift capacity from not having a working tool suspended from the machine. Since the quick coupler will weigh less than the pin-on bucket, a net increase in lifting capacity is achieved."
Geometry linked to performance
Excavator performance is closely linked to the geometry of the boom and dipper stick. "In general, the length of the quick coupler affects the breakout force of the machine," says Jacobson. "Since the breakout force is determined by bucket cylinder force and the radius from stick pin pivot to the tip of the bucket, any coupler that increases this radius has a negative impact on breakout force."
To compensate for decreased performance, a bucket with a smaller capacity and a decreased tip radius may be the best choice. For example, Liebherr manufactures a range of buckets that are specifically designed to work in combination with the Liebherr quick-coupler system.
"There is no change in cutting width from a standard pin-on bucket. However, the tip radius and bucket capacities are slightly reduced," says Jacobson. "Tip radius is reduced to counteract the slight decrease in breakout force that results when adding a quick coupler."
Likewise, ESCO has designed a bucket that compensates for a quick coupler. "The ESCO Scoop bucket has the attachment pins integrated into the shell of the bucket so when a coupler is used, the breakout force reduction is minimized," says Yoresen.
Yet, many times, use of a quick coupler will not influence bucket choice. "While most quick couplers (pin grabber variety) will add to the total rotational geometry (tip radius) of a bucket and coupler combination, the decision to add a quick coupler should not affect your bucket selection," says DeWeese. "However, the operator will need to be aware of the additional length for any interference."
Mechanical vs. hydraulic
Both mechanical and hydraulic quick couplers are available.
"The largest difference between your coupler choice is whether or not your machine is already plumbed with auxiliary hydraulics to the end of the dipper stick," says DeWeese. "Adding auxiliary hydraulics as an aftermarket option can get costly, and may make the mechanical coupler your more economical choice. The hydraulic version of the coupler makes your connect and disconnect much quicker."
Jacobson agrees that the choice is really a matter of the initial investment cost. "However, if tools have to be changed often, the initial cost savings of the mechanical quick coupler will be quickly offset by labor costs and downtime of the machine," he points out. "After all, if the operator is manually changing the coupler, he is of course not operating the machine, and therefore the machine is temporarily out of production."
Kenco Corp. manufactures both mechanical and hydraulic quick couplers. "Our mechanical-style Wedge Lock coupler is simple, light and very reliable," says Black. "The hydraulic version is slightly heavier, but it allows the operator to change attachments in about one quarter of the time."
Pin spacing issues
The pin spacings on a bucket are designed to optimize performance on a particular machine. These spacing will vary between brands.
Some quick couplers — multi-pin grabber types — are designed to accommodate the different pin configurations so many different buckets can be used on a given machine. Other couplers are designed to optimize the performance of a given brand of bucket and machine.
"Liebherr quick couplers are specifically designed to work with Liebherr quick-coupler buckets," says Jacobson. "The bucket pin spacings are designed to maximize the available forces of the excavator."
The system is not a "multi-pin grabber" — it can't adapt to different bucket spacings, he notes. However, adapter plates can be fitted to an existing bucket or hydraulic tool, regardless of the manufacturer. This allows the bucket or tool to be used with a machine outfitted with the Liebherr QC system.
Werk-Brau couplers are also tailored to individual machines. "Our couplers are pin-specific to the work tool being utilized," says DeWeese. "For example, a coupler fitting a John Deere 200 excavator and utilizing John Deere 200 attachments would match the original specifications of that machine and attachment, both for pin center to center and the stick/link width.
"Conversely, our combination coupler enables the user to utilize attachments not specific to the machine," says DeWeese. "For example, [you have] the same John Deere 200 machine, but the customer has Caterpillar 320 attachments. The top of the coupler is designed to the original specifications of the John Deere 200, and the bottom of the coupler is designed to the original specifications of the Caterpillar 320."
ESCO Multi-Pin Grabber couplers can pick up attachments with different pin spacing. "They continue to be popular with both end users and distributors because they can use attachments in their equipment fleet that are made for multiple machines," says Yoresen. "Because the ESCO coupler uses full system hydraulic pressure, there is a tight fit on the bucket pins, ensuring no reduction in machine performance due to a variance in pin centers."
Kenco Corp. offers a pin grabbing-style coupler that allows you to share different brands of buckets. "Our Wedge Lock couplers are typically 40% to 50% lighter than your typical pin grabbing-style coupler," says Black. "You lose absolutely no breakout force. Once the Wedge Lock coupler is mated to the Wedge lugging, the OEM tip radius actually remains unchanged. This allows the versatility of a coupler without compromising the machine's power.
"The couplers are machine specific, but the lugging is not," he adds. "By keeping the outside of each coupler the same (in a given weight class), you can actually share buckets with all brands of excavators."
Retention devices
"Safety is the most important feature when choosing a quick coupler," says Yoresen. "Important features to remember... include a sound design that ensures easy pick up; hydraulic check valves that will not allow the cylinder to retract in the event of a hydraulic failure; and visible non-hydraulic backup safety systems that prevent the coupler from prematurely releasing an attachment."
Quick couplers need to keep the attachment secure even when the carrier loses power. For example, the Liebherr quick-coupler system is designed as a positive lock system. This means that once the quick coupler is locked, no force must be continually applied to ensure the tool remains locked in place.
"In fact, just the opposite is true," says Jacobson. "Once the Liebherr quick-coupler system is locked into place, a force must be initially applied to unlock or de-couple the system. There is no need to rely on pressure sensors to know that the coupler is correctly locked."
Kenco Wedge Lock couplers also incorporate positive locking devices. "Our Wedge Lock coupler utilizes two bolts to draw the wedge bar tight to the bucket lugging," says Black. "This creates a positive locking action and prevents unintentional separation between coupler and attachment. Our hydraulic Wedge Lock coupler incorporates two coil springs with a safety latch to retain the wedge bar in case of a hydraulic failure."
A focus on safety
"The latest advancements in coupler technology are first and foremost designed around maximum safety techniques," says DeWeese. "The key design features in any coupler should be the use of static or manual safety pins clearly marked so that the operator and ground crew are sure of coupler engagement."
Consider the latest couplers from Werk-Brau. "We have added manual safety pins to both the main stick connection and the link connection for maximum safety and retention," says DeWeese. "Pins are manually inserted and removed by the operator or ground crew to ensure connectivity and engagement."
You should also be aware of how the quick coupler and tool fit together in terms of pin center to center, and the width of the coupler where it attaches to the tool. A good fit will increase the wear life. "Multiple pin center couples, while convenient, can leave a portion of the attachment pin exposed to shear forces or deformation of pins," says DeWeese.
ESCO is also bringing new technology to the market with the introduction of its TwinLock Hydraulic Coupler. "It features a dual blocking bar that holds the hydraulic cylinder in place; a front safety latch that is visible from the machine's cab; and a retaining jaw that holds the front bucket pin in the event the rear hook fails to grab the attachment pin," Yoresen points out. "All three of these safety improvements are independent of the machine's hydraulics, and do not require the operator to leave the cab."
Of course, not all advancements relate to safety. Some recent hydraulic quick-coupler designs not only couple the working tool (i.e., a hammer or vibrating compactor), but all the hydraulic connections associated with the tool.
For example, Liebherr's LIKUFIX system allows the operator to change between different hydraulic tools without leaving the cab or requiring another worker to manually connect hydraulic hoses. "Not requiring the operator to leave the cab of the machine saves time and increases productivity," says Jacobson.
For more information, visit www.ForConstructionPros.com
author: By Curt Bennink