The Evolution Of Forklifts
The first seated counterbalance forklift was built in 1918, featuring a gasoline-powered engine that required manual cranking to start. This early machine, designed for material handling, was the first to combine an engine, frame, transmission, brakes, wheels, and a steering system into a single vehicle. It was created to transport materials between different work areas, reducing the need for manual labor and improving overall efficiency.
Later in the 1920s, forklift manufacturers began to develop and utilize hydraulic systems. This system consisted of hydraulic cylinders, pump and control valve, replacing the older gear-driven chain and pulley assembly used for lifting. Forklifts enjoyed the advantage of higher capacities and smoother operation by utilizing hydraulics.
In the mid- to late-1930s, increased manufacturing levels spurred more innovations in the design and capabilities of electric forklifts, such as adding electrical systems. Eventually, large electric forklifts were introduced, giving customers a higher-capacity alternative with the same features of smaller models, only enhanced with greater lifting capabilities.
Thus the forklift evolved. From the earliest incorporation of a motor, transmission, drive components and wheels mounted on the frame, the equipment was continually improved. From its beginnings, forklift development and design has been in response to safe and productive material handling applications.
Classification Of Forklifts And Industrial Trucks
In order to categorize and differentiate between the various models of material handling equipment, the Industrial Truck Association (ITA) classifies industrial vehicles into 7 categories.
- Class I: Electric-motor powered, sit-down rider, counterbalanced forklifts that may be cushion or pneumatic tire vehicles. These models are often used in areas requiring pollution free operation such as food processing, freezers or general warehousing.
- Class II: Electric-motor powered, narrow aisle vehicles utilizing a solid tire design. There are many variations of Class II vehicles such as reach trucks, order pickers, low lift pallet and platform lifts. Reach trucks are designed to be used in narrow aisles and are equipped with a pantagraph attachment that allows the forks to be extended into the rack. Order pickers are designed to allow the operator to be raised with the platform. This allows the operator to “pick” small loads at different rack levels and stack the items on a pallet located behind the operator’s compartment.
- Class III: Electric-motor powered, walkie or walkie/rider vehicles utilizing a solid tire design. Sometimes called powered pallet trucks, the operator generally walks with the vehicle or rides in a standing position.
- Class IV: Internal combustion, sit-down rider, cushion tire, counterbalanced forklifts. These vehicles are intended for use on smooth, hard surfaces in wet or dry conditions.
- Class V: Internal combustion, rider type, pneumatic tire, counterbalanced forklifts designed for travel on rough surfaces such as earth or gravel roads.
- Class VI: Internal combustion or battery powered tow tractor models utilizing cushion or pneumatic tires.
- Class VII: Rough terrain forklifts.
Forklift Hydraulics
Forklift hydraulic systems are essential for the efficient lifting, tilting, and steering operations of the machine. These systems operate on the principle that liquids are incompressible, allowing hydraulic fluid to transmit force through a network of components.
Components And Operation
The core components of a forklift's hydraulic system include a reservoir (or sump) for hydraulic fluid, a pump, a series of tubes, and hydraulic cylinders. The pump moves the fluid from the reservoir into the tubing system, creating pressure measured in gallons per minute (GPM). Due to the incompressible nature of the fluid, this pressure is utilized to perform work. When pressurized fluid enters a sealed cylinder containing a rod, the fluid seeks the path of least resistance, pushing the rod outward to perform tasks such as lifting or tilting.
Types Of Forklift Hydraulic Cylinders
Forklifts employ various hydraulic cylinders, each designed for specific functions:
- Lift Cylinders: These single-acting cylinders receive the highest volume of fluid flow. They push in one direction to raise the forklift's mast and load.
- Tilt Cylinders: Typically double-acting, these cylinders allow hydraulic fluid to move the piston in both directions, enabling the mast to tilt forward and backward.
- Power Steering Cylinders: Also double-acting, these cylinders facilitate the steering mechanism by allowing fluid to move the piston in both directions, aiding in maneuverability.
Cylinder Designs
Hydraulic cylinders in forklifts are designed in two primary configurations:
- Ram-Type Cylinders: These utilize a rod with a consistent diameter that fits closely into the cylinder, sealed to prevent fluid leaks. They are commonly used in single-direction applications, such as lift cylinders.
- Piston-Type Cylinders: Featuring a rod with an attached piston, these cylinders allow hydraulic fluid to push the piston in either direction. Seals on the piston maintain pressure on both sides, making them suitable for applications requiring movement in both directions, like tilt and power steering cylinders.
Understanding these components and their functions is crucial for the proper operation and maintenance of forklifts, ensuring safety and efficiency in material handling tasks. Contact ProLift for support with forklift maintenance, service and repair.
