When there is a continuous flow of materials, such as mail or other documents to be distributed throughout a multistory building, conveyer systems may provide an economical supplement to elevators. In some installations, 200 lb or more of paper work and light supplies are circulated per minute.
Two types of conveyer systems are employed in commercial buildings. The selective vertical conveyer moves plastic tubs from one floor to another, automatically loading and unloading at preselected floors. The tubs typically are made to carry mail and small supplies and have payloads of up to 50 lb each. A typical selective vertical conveyer installation is similar to an escalator (Art. 16.4). A continuous roller chain is driven by an electric motor. Engaging sprockets at top and bottom, the chain extends the height of the building, or to the uppermost floor to be served. Carriers spaced at intervals along it transport trays from floor to floor at a speed of about 70 ft /min.
Another conveyer type, the tracked conveyer system, permits both vertical and horizontal document distribution. This system employs self-powered cars, which travel over a track system that allows switching off at selected station locations (Fig. 16.18). Where a specific floor may have a high volume of traffic, the track may be routed around the floor to one or more remote stations. The destination is programmed at the dispatching station, and the car is automatically switched onto the main track to begin its journey. Cars for this type of conveyer are generally limited to a maximum payload of 20 lb, although some are modified to carry up to 25 lb. The cars travel at about 100 ft /min.
For vertical track sections, a gear engages a continuous rack on the track for positive control in both the up and down directions. A friction-drive system is employed on horizontal track sections. Shaft-mounted machinery is minimized with the tracked conveyer system.
Like elevators, however, vertical conveyers must be enclosed in fire-resistant shafts. Generally, the only visual evidences of the existence of the installation are the wall cutouts for receiving and dispatching runoffs at each floor. In event of fire, vertical sliding doors, released by fusible links, should snap down over the openings, sealing off the conveyer shaft at each floor.
Vertical Conveyers. Operation of vertical conveyers is simple. When the tray or car is ready for dispatch, the attendant sets the floor-selector dial or presses a button alongside the dispatch cutout. For the selective vertical conveyer, trays are placed on the loading station, where they are automatically moved into the path of the traveling carriers. Each tray rides up and around the top sprocket and is automatically discharged on the downward trip at the preselected floor.
The best place to install a vertical conveyer is in a central location, next to other vertical shafts, to minimize horizontal runs in collecting and distributing correspondence at each level. The choice of conveyer types should be based on the needs of the user. The selective vertical conveyer is appropriate where the required movement is entirely vertical, while the tracked conveyer system lends itself to both horizontal and vertical layouts.
Pneumatic Tubes. These are also used to transport small loads within buildings.
Units are moved through tubes under air pressure or suction, or both. Items to be transported are carried inside cylinders slightly smaller in diameter than the tubes.
In choosing between vertical conveyers and pneumatic tubes, the designers first consideration should be the size of the load to be carried. The traveling cylinder is limited as to the size and weight of the material to be moved. Aside from that, an arterial system of pneumatic tubes may satisfy the requirements of a predominantly horizontal building, whereas a vertical conveyer is generally more advantageous in a tall building.