Copyright Goodheart-Willcox Co., Inc. Chapter 16 Conditioning and Distribution of Compressed Air 415 Adequately sized distribution lines are critical to the operation of a pneumatic system. The cost of the conductors is only a small part of the total installa- tion cost. Therefore, when an estimated fl ow rate falls between conductor sizes, the larger size should be installed. The larger conductor will increase the per- formance of the current system and provide increased capacity for future system expansion. 16.4.2 Flexible Conductors Hoses and semirigid plastic tubing are examples of fl exible conductors used extensively in pneumatic sys- tems, Figure 16-26. Hose applications include tempo- rary distribution lines for portable-compressor setups, connections between movable machine members, and connections between the FRL unit of a workstation and air-powered tools. Semirigid plastic tubing is often used in small equipment as the primary conductor between components. It is also used as sensing and control lines in many other compressed-air applications. Hose is constructed with a minimum of three lay- ers of materials: • Inner tube providing a smooth surface to minimize airfl ow resistance. • Middle section containing woven reinforcing materials to withstand system pressure. • Outer layer to protect the hose from damage resulting from handling and the abrasive and corrosive materials encountered in the work environment. receive careful consideration. The sizing of conductors can be done only after the volume of air and the location of the workstations have been established. The objec- tive is to hold pressure losses between the receiver at the compressor station and the workstation to less than 10% of the receiver pressure. Both the conductors and the associated fi ttings must be considered, Figure 16-25. Tables are available in engineering handbooks that provide data on the air pressure loss in rigid conduc- tors transferring a specifi c volume of compressed air expressed in cubic feet per minute (cfm). These pressure- loss fi gures are typically given as the loss per 100 feet of conductor of a specifi c nominal size and schedule rating. Tables are also available indicating the pressure losses caused by the common fi ttings used in distribu- tion lines. The pressure loss caused by these fi ttings is given in feet of comparable-sized straight conductor. Determining the correct size of conductor for various sections of the distribution system requires the development of a map of the air needed, in cfm, at the junction points of the main distribution lines and each workstation drop line. This map can be con- structed by starting at the point that is the greatest dis- tance from the compressor station receiver and adding the air needed by each station. These fi gures must be increased by 10% to cover air leakage in the system. An estimated air volume should be added to these fi gures to cover the air needed for future system expansion. The resulting fl ow rates can then be used to select a pipe size that will deliver air at a pressure drop lower than the recommended level. IMI Norgren, Inc. Figure 16-25. The fittings used in distribution lines produce a pressure loss. Pressure loss for each fitting must be included as part of the total loss in the system. Atlas Copco Figure 16-26. A wide variety of hose and semirigid tubing is available for use in pneumatic systems.