A forklift truck is the machine most people think of when they hear the term mobile equipment. It is by far the most common and useful of the various vehicles that fall under that description. Manlifts, boom trucks, and cranes all have their uses, but none as often or as broad in scope as a forklift. They are so common that high school students are often trained to use them for summer jobs at warehouse-style stores. In reality though, they're just as often told to have a seat and figure it out as they go as they are properly trained.
The forklift truck looks like a small, one seat car with L-shaped forks (typically about 4 feet long) protruding from the front on an adjustable boom, although some smaller battery powered models have a space for the operator to stand rather than sit. The cab has a steering wheel, horn, seat with seat belt, an overhead guard to protect the operator, gas and brake pedals, and several switches or levers that control the hydraulics. They typically also have headlights and optional floodlights, and a backup signal. At the back of the cab is a large, heavy counterweight which helps the truck maintain its center of gravity while transporting a load. The engine powers a hydraulic system in addition to powering the wheels. In addition to controlling the forks, the hydraulics also provide power steering for the wheels. A forklift's turning wheels are in the back, not the front, to provide extra maneuverability at the price of some stability. For this reason, forklifts are not driven at high speeds.
Forklift trucks are designed primarily to lift and move heavy loads on pallets. In this respect they are similar to pallet jacks, and moreso to battery powered self-propelled pallet jacks. Forklift trucks are different in that the operator rides in the cab of the forklift, in most cases operating it much like an automobile. Some models are battery powered, especially ones intended for use inside grocery stores or other areas where exhaust would be inappropriate. More powerful models are powered by propane tanks, gasoline, or diesel fuel. With a forklift, the strength of the operator is meaningless. Any man, woman, or child can lift a load weighing several tons and carry it around with ease.
In addition to lifting pallets (and whatever is on them), forklifts are also used to lift certain types of bulk storage totes and heavy machines, such as commercial-grade air conditioners, which have slots built-in designed to accept the forks. Many other types of mobile equipment have fork slots as well so they can be carted around with a forklift in case they break down, or need to be set up on a flatbed truck for transportation, or even if they just don't move fast enough on their own to get to the job site.
Options and Attachments
The levers and controls on fork trucks vary from model to model. The forks can typically be made to do any or all of the following via the hydraulic system:
Lift: The forks can be made to raise up off the ground, to clear obstructions, lift loads, or bring them down from a height. This feature is found on all fork lifts. Some booms are capable of telescoping, allowing the forks to raise much higher than the forklift is tall.
Tilt: The boom can be tilted back and forth off of level, to reach into awkward places or rest a load against the boom so it doesn't fall forward.
Spread: The forks can be made to separate or be brought together, to adjust for different shapes and sizes of loads and the fork slots built into them. Many models without powered spreading are adjustable by hand, when there is no load on them.
Side-shift: The forks can be made to shift left or right, to adjust for the forklift being off-center with respect to the load, or to push the load up firmly against the side of another load.
Rotate: Certain fork trucks with a clamp attachment can rotate the load, to set it down on its side or its top.
A number of attachments are available for forklift trucks to expand their capabilities. Some attachments are designed to slide onto the forks, while others replace them on the boom. A crane attachment is a horizontal boom that slides over the forks to provide extra reach and a way to sling a load underneath the forks, rather than rest on top of the forks. Fork extenders are sleeves that slide over the existing forks and make them longer. Barrel clamps replace the forks, and use the side-shift hydraulics to open and close curved clamps that fit around cylindrical barrels for a secure lift. Box clamps are similar to barrel clamps except they are flat instead of curved for picking up square objects. Some barrel and box clamps can rotate. Forklifts that need to carry hollow cylinders such as tubes, rolls, or coils replace the forks with a single shaft, or use an attachment that slides over the forks with a shaft slung underneath.
The power of a forklift is what makes it useful, but it also makes it dangerous. A forklift can weigh a few tons itself, and can drive around at a pretty good clip (although much slower than a car). This gives it a great deal of momentum, especially when carrying a heavy load. A forklift impacting a structural steel building column can bend and twist or even break it. It can do much more damage to expensive equipment and people if the operator is not careful. The forks can pierce the plywood sides of a semi truck with no trouble at all. To ensure the forks don't get caught on anything on the floor, it is a good idea to drive around with them about 4-6 inches off the ground. Driving around with them any higher creates additional safety problems. And of course, the operator should always watch where he is going and sound the horn at blind corners.
Likewise carrying around several tons of load must be done carefully. Sharp turns at speed with a large load can easily tip the forklift over. The forklift should never be driven around while the load is raised, because that also throws off its center of gravity. Loads can also block the operator's view, so the forklift is typically driven in reverse when carrying large objects.
Other workers in the area need to be aware of the forklift and give it the right-of-way. They need to stand clear of any maneuvering the forklift needs to do, and never under any circumstances step over or underneath the forks. The forklift should not be used to lift people without special equipment intended specifically for that purpose. The most jaw-droppingly unsafe use of a forklift I have ever seen is currently being distributed around the internet in a variety of e-mails and funny picture galleries. It is a forklift lifting another forklift with a load in its forks to provide the extra elevation necessary to get the load up to a balcony. In addition, two workers are standing on the elevated forklift. A larger forklift or a crane should obviously have been used instead.
Extra care should be used when loading a truck with a forklift. The truck must be secured with wheel chocks, a dock-lock if available, and the truck's handbrake to prevent trailer creep. Trailer creep is a result of the action-reaction forces on the truck by the action of the forklift driving on it, which can push an unsecured truck away from the dock and cause the forklift to fall off. Additionally, a jack stand should be used to prevent the trailer from tilting forward if it is not attached to its tractor, and a ramp covers the gap and adjusts for elevation differences between the truck and the loading dock.
As far as the operator is concerned, he should wear his seat belt at all times while the engine is running, and if the forklift tips over he should remain in the cab rather than try to escape. The forklift could crush an operator who tries to get out from a falling cab. As with cranes and other equipment that is capable of reaching high into the air, loads should not be lifted under power lines.
There is another kind of forklift called a telescoping forklift, which looks similar to a crane or a boom lift except with forks at the end of the boom. These are used to lift loads up to higher levels than a standard forklift can reach, or reach across obstructions that would stop a standard forklift. However they are not as maneuverable and need much more room to operate.
Much like a forklift can accept attachments to duplicate the actions of other equipment, other equipment can be supplied with forklift attachments. A crane can suspend a pair of forks off the end of its hook, but care must be taken to control the load from spinning. A bulldozer or a front-end loader could replace its blade or bucket with a pair of forks as well, creating a very powerful forklift, although this would not be used indoors or for loading a truck. The versatile Bobcat line of light construction vehicles, of course, also has a forklift attachment.