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Pallet storage generally falls into one of three categories. The most commonly used system is pallet racking, of which there are several types. Another means of storage is the mezzanine. Automated storage and retrieval systems (ASRS), which brings high-tech equipment to what is traditionally a low-tech industry, is the third type of storage system.
The selective pallet rack that stores pallets only one unit deep is the type most often used. A selective pallet rack consists of upright and cross beams that form a structure on which heavy-duty shelves are laid. Set up individually or connected horizontally to others, selective pallet racks can rise as high as the weight of the pallets and the strength of the racks will permit. The reach of the forklift, which loads and unloads the pallets, is also a determining factor in the height of the racks.
Push-back pallet racks provide greater depth and can store pallets two to five deep. Pallets rest on sturdy carts that slide back and forth on continuous rails set in individual lanes. As pallets in the front of a line are removed, those in the back automatically move forward. New arrivals push back existing pallets, and the last ones in are the first to be removed.
Like push-back systems, drive-in pallet storage systems store pallets in depth and operate on the last-in, first-out system. Forklift access is from one end only. Drive–through systems are similar except for the fact that they are open on both ends, allowing access from either direction.
Gravity-flow racking lends itself to high-density, first-in, first-out inventory management which is desirable for products with limited shelf life. As its name suggests, this system relies on gravity to ease pallets forward on slightly inclined rails when the front pallet is removed. Pallets are loaded from the higher end in the rear, and removed from the lower front end.
Mezzanine pallet storage is not usually a permanent storage system. Rather, the mezzanine is a temporary floor constructed between two permanent floors of a warehouse, store or storage area. It is useful for relatively short-term storage of overstocks, seasonal items or special-promotion inventory. Mezzanine storage is a cost efficient means of acquiring extra storage because it can be taken apart and moved to another location or stored until it is needed again.
The automated storage and retrieval system (ASRS) is the newest system of pallet storage. It employs computers and trained operators to store and retrieve pallets. Specialized machinery places pallets in assigned locations then moves them to designated destinations within the facility as needed. Despite the obvious labor savings the system affords, it is expensive to install and may have high maintenance costs.