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Hydraulic Dock Levelers Stop Stump Out

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Safety and productivity are major considerations when you select any sort of production equipment and dock levelers are no exception. One issue causing real safety in operational concerns of the dock is a situation known as stump out. This problem is associated with mechanical or spring powered dock levelers as well as newer power assisted models. Two factors are making stump out an increasing concern. Trailer bed heights are getting lower and more trailers are equipped with air ride suspensions. Let's take a look at the cause, results and solution for stump out.
So what causes stomp out? This is a mechanical or power assisted dock leveler equipped with mechanical safety legs. All dock levelers are required to provide a method of free fall protection to help prevent dangerous accidents that could result if the truck were to separate from the dock while it is being loaded or unloaded.
Mechanical safety legs can help stop the leveler's rapid fall in this situation but they can also be a source of problems. Levelers come to rest on the trailer bed a few inches above the dock height. Here the safety legs hang above the frame posts on which they rest when the the level is in the stored position.
As the trailer is being loaded the weight of the forklift entering and leaving causes the trailer bed height to fluctuate from above to below dock height. This movement can be dramatic. Up to eight inches on trailers with air ride suspensions. When the trailer bed drops below dock height the leveler safety legs hit the frame posts and the leveler platform cannot follow the trailer bed down. Now the level lip adopts a steep slope to reach the trailer bed and here's where the problems begin.
This is a stump out situation. And it can have dramatic effects. Every time a forklift impacts the steep slope the forklift driver, load and leveler takes a beating. Serious and costly neck and back injuries are possible and the forklift and load our jarred. The forklift steering, linkage, tires and counterweight can all be damaged. Also, since the impact intended for the leveler of platform is now delivered squarely to the leveler lip, you can expect damage to the leveler platform, lip hinge, front header and rear hinge.
How can stump out be prevented? Well most mechanical and power assisted levelers come with pull chains to retract the safety legs when the leveler is lowered to service the low-dock trailers. With the legs retracted, stump out does not occur but if the leveler is resting on the trailer bed just an inch or two below dock height, stump out can occur.
As the forklift unloads the trailer the bed height gradually rises. As soon as the bed height reaches dock level, the safety legs snap back into position. When the forklift enters again the bed drops, the leveler lip returns to the steep slope position and the stump out problems are back.
The only sure way to avoid stump out problems is did to choose a leveler with full range free float. Only hydraulic levelers offer this advantage. Instead of mechanical safety legs, hydraulic levelers have velocity fuse free fall protection. This allows the leveler to go below dock without having to retract any legs. Not only does the velocity fuse provide better free fall protection than retractable safety legs, it also is ergonomically better as it eliminates the need for workers to bend over to pull that chain.
As the forklift travels across a hydraulic leveler you'll notice the steady contact with the trailer bed as it moves above and below dock level. The leveler platform and lip form a smooth path for minimal impact.
Remember, with mechanical safety legs the potential for stump out is always there. Only hydraulic levelers offer a full range free float to help guarantee save, smooth transition.
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