Truck design and operation

To drive a truck safely and do a proper daily inspection you must know the machine: what the parts are called, what they do and how they work together. Knowledge of the truck's construction and operation is a separate learning objective on the certification course. Here a counterbalanced truck — the most common type — is covered part by part.

The chassis is the load-bearing frame that holds it all together. At the back sits the counterweight — a heavy block (often cast iron) that balances the load the forks lift in front. The entire stability principle rests on this: the front axle is the pivot point, the load in front creates a tipping moment and the counterweight at the back provides the stabilising counter-moment (see the entry on stability). On an electric-powered truck, the heavy battery functions as part of the counterweight — therefore there is an allowed minimum and maximum battery weight on the type plate.

At the front is the drive axle with the load-bearing, driving front wheels; at the rear is the steering axle with the steering rear wheels (this is why the rear swings out in turns — see the driving technique entry). The tyre type is shown on the nameplate and has major significance: pneumatic tyres give best suspension outdoors; solid and polyurethane tyres are typically used indoors where puncture is to be avoided. Tyre type affects both stability, suspension (and thus vibration) and which ground surfaces the truck can run on.

The mast is the vertical rail in front that the carriage runs up and down. The forks attach to the carriage and can be moved sideways to fit the pallet. The mast can be tilted a few degrees back and forth: tilted back makes the load rest against the backrest during travel, tilted forward is used to set the load flat onto a shelf.

• 01Mast type (duplex/triplex/special) determines lift height and FREE LIFT — how high the forks can be raised before the mast itself begins to telescope upward. Full free lift is critical in containers and low spaces (see the post about mast types).
• 02The lifting chains run over pulleys at the top of the movable mast sections and pull the sled up when the lifting cylinder is extended — they must be inspected for wear and correct, even tension.
• 03The backrest (load back) behind the forks keeps the load from tipping towards the mast.

Lifting, lowering and tilt are driven hydraulically. The principle is that a pump puts oil under pressure, and that pressure is converted to movement in cylinders:

• 01The hydraulic pump (driven by the combustion engine or an electric motor) draws oil from the tank and pressurises it.
• 02The lifting cylinder(s) push the mast's slide upward; via the lift chains the forks are raised.
• 03The tilt cylinders (one on each side) tilt the mast back and forth.
• 04If a side shift or other accessory is mounted, it is supplied by an extra hydraulic function ("third function").
• 05The control valves (operated from the levers) distribute the oil to the right cylinder.

The steering acts on the rear wheels and is usually hydraulically power-assisted, so a small steering wheel can turn the load-carrying rear wheels. The drive comes either from an internal combustion engine (diesel, gas/LPG) via a transmission — often a torque converter or hydrostatic drive — or from an electric motor powered by the truck's battery. A direction selector switches between forward and reverse; on most trucks you can change direction smoothly to manoeuvre forward and backward in tight spaces.