Copyright Goodheart-Willcox Co., Inc. Chapter 16 Conditioning and Distribution of Compressed Air 403 while providing easier access for maintenance because of the lower number of compressor stations. In theory, the centralized grid allows fl exibility for rearranging workstations since the grid can be accessed at any point. These systems can be effective if original planning of the facility provided adequate capacity for the increased air consumption. However, the single, main supply line can create pressure drops on the end branches if the air demand of a worksta- tion close to the compressor station substantially increases. The decentralized grid design uses individual compressors in several locations to provide com- pressed air for one or, at the most, a small number of workstations. This design allows each of the decen- tralized grids to function as independent systems. Figure 16-9 shows a decentralized grid system con- taining three independent compressor installations. This design is sometimes referred to as a unit system. The air from each independently operating com- pressor powers a single, large piece of equipment or a small grid serving a group of workstations in a manu- facturing cell. This design is considered more fl exible than the centralized grid, although the capacity of each unit must be adequate to absorb changes caused by relocating or resizing equipment. In some installations, the individual, decentralized systems are connected together. This is an attempt to equalize pressure to improve the effectiveness of each of the unit sections. The loop system distributes air through a main line that forms a continuous loop, Figure 16-10. The loop-shaped main distribution line provides maxi- mum airfl ow with a minimum of fl ow resistance. The design may use a single compressor location or mul- tiple compressors that are dispersed around the loop. If the system uses a single compressor, the air is fed into the loop at one location. A workstation located minimal pressure drop in the lines to ensure satisfac- tory operation of the workstation tools and minimize operating costs. A variety of designs are used to ensure the transported air remains pressurized, is delivered at the required volume, and is free from moisture and other contaminants. A distribution system may be as simple as a fl exible hose leading from a portable com- pressor to a portable hand tool. On the other hand, it may be as complex as an elaborate grid delivering air in a large production plant. 16.2.1 Distribution System Designs Distribution systems may be grouped into four general categories: • Fixed-piping, centralized-grid system. • Fixed-piping, decentralized-grid system. • Fixed-piping, loop system. • Flexible hoses used with portable compressors. The design that is selected depends on the size of the installation and the level of demand for com- pressed air. The centralized grid design distributes air from one central location to all workstations in a facility. This design uses one or more compressors at a single compressor station with air piped to each workstation in the facility via fi xed piping. The single compressor station is connected to a large central line with small feeder lines branching out to individual workstations. This design is sometimes called a dead end or tree sys- tem. Figure 16-8 illustrates a simple, centralized grid that still exists in many industrial facilities. The illustra- tion shows feeder lines that balance distribution capa- bility on both sides of the central line. This distribution design allows the use of larger compressor equipment Feeder lines Compressor station Goodheart-Willcox Publisher Figure 16-8. A centralized grid is a common design for an air-distribution system. An actual system is usually not as symmetrical as shown in this illustration.