Copyright Goodheart-Willcox Co., Inc. 406 Fluid Power air. The additional receiver is located close to the high- demand equipment. It supplies the extra air needed to prevent an excessive drop in distribution-line pressure. This arrangement is cost effective as it can be used to reduce construction cost related to the compressor and distribution line. It can also accommodate unexpected resizing or relocation of existing workstations. Auxil- iary receivers may also be used in loop-type distribu- tion systems to maintain a more uniform pressure as air demand changes in sections of the line. 16.3 Final Preparation of Air at the Workstation Compressed air is often used directly in process applica- tions. These applications may be involved in chemical, food, petroleum, or metal processing. In many of these situations, the air must be cleaner than typical, avail- able at multiple pressure levels, or contain lubricants to prolong the life of system components. These situations are common in manufacturing applications involving pneumatic-powered hand tools or complex machines powered and controlled by pneumatic actuators. This fi nal preparation is usually provided at each workstation. Three individually constructed compo- nents assembled as a combined fi lter/pressure regu- lator/lubricator (FRL) unit are normally used for this purpose. Figure 16-15 illustrates a typical FRL unit of the type used at individual workstations. The FRL unit removes any remaining unwanted particles in the com- pressed air, provides a means to readily adjust work- station air pressure, and provides lubricant to prolong the life of workstation components. 16.3.1 Air Filtration at the Workstation A fi lter is the fi rst component of the FRL unit. It is designed to remove any remaining unwanted particles in the compressed air. These particles include: • Airborne dirt. • Rust and scale that have broken free from the walls of the distribution lines. • Liquid water that has condensed in the distribution lines. • Atomized oil particles from the compressor. A variety of designs are used by fi lter manufactur- ers to remove these contaminants. The following is a brief description of a fi lter designed for an FRL unit. A two-stage fi ltering arrangement is commonly used in an FRL unit. The design involves both centrif- ugal force and porous materials to separate and trap unwanted particles. The porous material may be paper, metal, or ceramics. Air entering the intake port of the system operation. A fairly accurate time factor can be established by averaging the percentages of operating times of actuators based on time and motion studies using similar operations in existing equipment. Then, multiply by a load factor that is an estimated per- centage of maximum actuator load delivered during operation. The load factor is more diffi cult to establish and requires the assistance of experienced pneumatic system staff. Once the fi nal estimated air consumption has been determined, the pipe sizes can be selected for the dis- tribution system. Selection is based on the anticipated airfl ow rates and pressure drop caused by the lines and fi ttings in the system. 16.2.3 Other Distribution System Considerations A number of additional factors may affect the distribu- tion of air in a pneumatic system. Two common fac- tors encountered are the presence of liquid water in the distribution lines and excessive pressure drop caused by high, short-term air usage in sections of the system. The formation of liquid water is the result of the continued cooling of air in the lines. As previously discussed, the components in the compressor station remove a large portion of the water vapor that enters the system with the atmospheric air. However, some water vapor still remains in the compressed air. Liquid water forms if the temperature of the compressed air in the lines drops below the dew point. This situation may become a serious problem when distribution lines are exposed to low temperatures, such as during cooler seasons of the year. The liquid water that forms in the distribution lines can be removed by designing the lines with a slope. A pitch (slope) of 1″ per 10′ of line allows the water to accumulate at selected low points in the system. Drop lines from these low points lead to water traps where the water is removed, either manually or with an auto- matically operated device. See Figure 16-13. Another design feature that greatly reduces the entrance of liquid water into actuators is how the workstation is connected to the distribution system. The drop lines leading to the workstation should be attached to the top side of the distribution line. See Figure 16-14. The drop line should also include a water trap or drain trap that is lower than the worksta- tion outlet. This allows the accumulation and removal of any liquid water that forms in the drop line. If the system includes a high-demand piece of equipment, the air pressure in that section of the distri- bution system may drop excessively. If this equipment only occasionally operates, it may not be necessary to increase the size of the total system. The solution may be an auxiliary-air receiver to supply extra compressed