Maintenance/Management: Quick couplers

In the right applications there is nothing that can boost your excavator’s productivity more than a quick coupler.

Deric Wagner, vice president at WagMann (which sells the Wedgelock brand of coupler in the United States) cites a customer who was working in particularly difficult and rocky soil in California’s Sierra Mountains and having to change from ripping to loading buckets constantly. When they counted up the average number of bucket changes their excavators performed it ranged from 120 to 160 changes per machine per day. “Being able to switch buckets quickly was integral to their business,” Wagner says.

“Machines are getting more capable every year,” says Dale DeWeese, national sales manager for Werk-Brau. “With these capabilities they are able to take on more jobs, but to be fully effective they need a quick way to change attachments.” Without a quick coupler, the pins can become rusty and difficult to hammer out, and some can weigh as much as 100 pounds, making them difficult to handle once they do come out. “Once you drive pins and then move to a quick coupler, you never want to drive pins again,” DeWeese says.

Government intervention
In August 2004 the federal Occupational Safety and Health Administration raised concerns within the attachment coupler segment of the heavy equipment industry with the publication of its bulletin Hazards of Unintended Release of Buckets from Quick Couplers on Hydraulic Excavators. The bulletin asked manufacturers to provide and contractors to use couplers that have a manual secondary safety system that is independent of the hydraulic circuit to prevent accidental release of the bucket.

“The whole point of a hydraulic quick coupler is you don’t have to get out of the cab to change the bucket,” says Ray Corrigan, West Coast sales and technical and hydraulic support at Geith. “The operator is not going to get out of the cab on a cold and frosty morning to look for a safety pin and insert it. Unless you stand over an operator, he’s not going to do it.”

Manufacturers were upset that the original ruling not only killed the one advantage quick couplers offered, but it also turned a blind eye to the hydraulically applied secondary locking systems some manufacturers already offered. There was concern, too, that all the deaths associated with buckets detaching from quick couplers were due to operator negligence (and not any design defect) and that asking operators to exit the cab to hammer in a locking pin would only invite further negligence.

OHSA decided to hold a meeting with all the quick coupler and excavator manufacturers to address these concerns in late 2004. The OSHA representative was open to the manufacturers’ ideas and focused on getting the job done right, says Russ Hutchison, director of product safety and technical services for the Association of Equipment Manufacturers. As a result, OSHA is expected to update its safety bulletin this year to require automatic backup safety systems that can be manual or automatic but that don’t necessarily require operators to leave the cab.

Here’s a look at the latest technology in the quick coupler world and what manufacturers are doing to make these components even safer.

Geith’s pin-grabber-style coupler is based on pin diameters and accepts everything from 45- to 120-millimeter pins. “We’ve designed the coupler with a horizontal ram with the length of the cylinder designed to suit the full variation in centers. We made it to pick up the narrowest pick-up width, which means if you put it on your machine it allows you to pick up any OEM manufacturer’s attachments with the same pin diameter,” says Corrigan.

“We have a bright green, high visibility front safety clasp which is spring retained and hydraulically removed and comes around the front pin. It’s the last thing to come off and the first thing to go back on and so the operator cannot operate the coupler unless it is safe. It has to be hydraulically removed, which means if you have a loss of hydraulic pressure you cannot remove it.”

Geith’s coupler uses a five-port valve to achieve its curl-to-open feature with the fifth port taking a signal from the rear of the bucket curling cylinder. The fifth port has a pressure relief setting that allows the coupler to open only when the bucket cylinder is fully bottomed out with the coupler curled all the way to the safe position. Two inline check valves also prevent release in the event of hydraulic failure. By using this hydraulic method of sensing the coupler’s position rather than gravity switches, you can be sure the coupler is in the safe position and the lock is not stuck by any mud, asphalt or grit that might cause it to remain in the open position.

Geith’s coupler is activated by a purpose designed control box in the cab, and to prevent accidental engagement it has a warning buzzer and is set on a five second delay that requires you to hit a second button to activate the coupler.

The RotoLoc design represents an evolution in JRB’s line of couplers, says James Baird, manager of marketing and custom works at JRB. It adjusts for multiple pin spreads, accepts multiple pin diameters and can be reversed for most attachments (enabling you to shovel with an excavator bucket, for instance).

The hook facing the cab on the RotoLoc picks up the front attachment pin, and only when the coupler is in the full curl position will the coupler lock and unlock. When the opposite hook pushes up against the back pin a cam comes down over the front pin. Then an independent safety lock is pulled into place when the cam is fully extended. Gravity assists the secondary lock in the unlocking sequence when the coupler is in the full curl position.” Even if the check valve were to fail, it physically can’t unlock itself,” Baird says.

JRB will also be introducing a new, low-pressure hydraulic system this year for its hydraulic couplers. It will have a five-second delay built into the solid state control box (which means not having to press a second button) and an external alarm that sounds during the five-second delay and alerts workers on the ground that the coupler is unlocking and to move away.

The company also makes a wedge-style SmartLoc coupler, a PowerLoc coupler and two single-pin-grabber-style couplers (one of which has the manual pin lock) and a completely mechanical coupler. “The customer’s choices are driven by time and money,” Baird says. “Probably only 2 percent of our sales are mechanical couplers anymore and those are into applications where the mechanical coupler is a necessity. Everyone has come to realize that it defeats the purpose. It’s faster than pounding pins, but it’s not nearly as fast as the hydraulic version.”

Kenco makes both a pin grabber and a dedicated, wedge-style coupler. The pin-grabber models use a high pressure system and the wedge style stays in place with low pressure.

“The check valve on the pin grabbers hold pressure in the event you would have a check valve failure, but our pin grabbers have two gravity cam locks inside them,” says Tracy Black, operations manager at Kenco. “If you want to change attachments you have to curl the bucket and crowd it all the way up to the machine in the full, rolled-in position and that lets those two cam locks fall out of place. Then you hit the button and actuate the hydraulic cylinder, which lets it open and release the bucket. Then you roll it back out and put the bucket down and grab the next one and curl it back to the machine in reverse process.”

Kenco’s designs include locking pins as well, Black says. “It has to be manually done, but we provide them with ours. We think it’s a good idea and we’ve put pins in ours from the start, so there was no need to retrofit,” he says.

A spring-loaded, hydraulically released Quick Tach is Werk-Brau’s latest pin grabber design and the fourth generation of its coupler line. “We took every component of safety we’ve developed over the past 12 years and incorporated it into this model,” says Dale DeWeese, national sales manager. It comes in manual and hydraulic versions. The spring holds the lock in place on the rear pin of the bucket and on the hydraulic model, hydraulic pressure overcomes the spring to release the lock. Once the locking mechanism is engaged, a secondary manual positive lock is installed that can only be put in if the coupler is 100 percent engaged with the bucket pins.

“It’s an over-center design that’s self adjusting,” says Greg Smith, chief engineer. “As the coupler wears, it remains tight. “The unique thing about ours is that it has just one moving part, which is the rear locking mechanism,” Smith says. “It’s very reliable and isn’t affected by dirt or debris.”

The Wedgelock quick coupler uses a wedge plate rather than swinging jaws to snug up the coupler against the pins, so it doesn’t get loose over time. The wedge slides in underneath the back pin, has fewer moving parts and infinitely adjusts for wear. “The wedge plate also offers a mechanical advantage, like a wedge pushing under a door,” says Matthew Calvert, managing director for the New Zealand-based company, “so it’s virtually self locking and doesn’t require a lot of pressure to hold it there.”

Additionally the Wedgelock’s hydraulic cylinder is machined out of a single block of steel and has the check valve, the return line and all the hydraulic plumbing machined into the block to eliminate the chance of external damage.

The Wedgelock coupler uses a manual safety drop lock to prevent accidental bucket releases. It also has a visual indicator bar that the operator can see on the coupler to know when the wedge is engaged and when it’s not. “Our system is extremely safe as demonstrated by field testing done where our quick couplers have no oil pressure after disconnecting the two hoses, removing the check valve and letting the oil bleed out of the cylinder,” Calvert says. “The wedge plate stays firmly locked onto the attachment pin.”

CE Attachments
The Edge branded coupler from CE Attachments is a spring-loaded coupler with a safety pin lock on it. “There are two different things you have to do when you remove your bucket and put your bucket on,” says Ron Peters, inside sales supervisor. “To remove it you have to pull the safety pin off first and then use your tool to unlock the coupler and then when installing it you put your safety pin through and then clip it on so the bucket cannot come off,” he says.

Quick coupler accidents
OSHA’s concern over deaths and injuries caused by quick couplers accidentally releasing buckets was well founded – but so far as anybody knows, none of these accidents were caused by a bad design or product failure. “It’s almost always more than one event,” says Russ Hutchison of AEM. “Usually one slip up is not enough.”

What typically happens in these accidents is:

  1. The operator gets careless or in a hurry and fails to properly engage the coupler.
  2. The operator, out of laziness, neglects to actuate the secondary lock.
  3. The mechanisms for the primary or secondary locking systems become worn or so poorly maintained they fail.
  4. The coupler and/or the bucket are overloaded or run to failure in applications they’re not designed to handle.
  5. Any combination of the above.

Pin grabber vs. dedicated coupler
There are two basic styles of quick couplers, the pin grabber and the dedicated style. The pin-grabber style adds enough length to the excavator boom to have a slightly negative impact on the breakout force and adds to the tip radius and weight. Standard pin grabbers are no more versatile than the dedicated systems, but multi-pin grabbers can pick up a wide range of buckets.

With the dedicated-style couplers you don’t lose any breakout force because you’re not changing the geometry in the relationship between the bucket and the boom. But a dedicated coupler can only pick up buckets with that style of “ears” to engage the coupler – and most OEMs make their own proprietary versions.

“You’re seeing a trend where people are going to the pin-grabber couplers because there are all these different small manufacturers making dedicated buckets and every one of those are different,” says Deric Wagner of WagMann. “If a customer needs a dedicated style of bucket right away, but the manufacturer is 12 weeks out, the customer is stuck.”

Improvements in mechanical locks
A quick coupler does not always mean a hydraulically activated device that eliminates the need to leave the cab when changing buckets. Several manufacturers we talked to also make a quick coupler that is, in fact, manually locked into place, but does so with less effort, time and manpower than a pin that has to be hammered through a hole.

“We had the simple cost effective design of inserting a manual safety pin about 15 years ago, but operators were not getting down from their warm cabs to insert it,” says Ray Corrigan at Geith. “A lot of the excuses people gave for not inserting a locking pin were that they lost the pin or that the pin was in the back of the service truck 100 miles away. I have even come across an operator who cut the head off the safety pin and welded it over the hole to give the impression that the pin was inserted.”

First-time users will sometimes buy the mechanical couplers as a stepping stone to a more sophisticated product, says Matthew Calvert at Wedgelock. “It gives them an entry to quick couplers without the expense of the hydraulic version,” he says. “With our mechanical version you use a wrench. Wind it up and it locks on tight. It’s not as popular in America. But in our market there is a lot of forestry and people working out in the bush. Downtime could be an issue if they break a hose and need a hose doctor to come to the site.”