Copyright Goodheart-Willcox Co., Inc. Chapter 16 Conditioning and Distribution of Compressed Air 399 Oil-bath fi lters have a fi lter medium that is constantly bathed in oil. The oil captures the dirt and transports it to a sump where it settles and is removed during periodic service. This style of fi lter was popular in older compres- sor systems and is still used in some applications today. Filters require regular servicing, regardless of their design. A fi lter that is clogged with dirt reduces system effi ciency by limiting the volume of air intake. Limiting intake volume reduces the output volume of the com- pressor and can cause overheating of the unit. A regular schedule should be developed for service of the intake fi l- ter based on the environment surrounding the pneumatic system and the duration of compressor operation. 16.1.2 Controlling Air Temperature The temperature of both the intake air and compressed air are critical considerations when working with a pneu- matic system. According to the general gas law, any change in the temperature of a gas is directly refl ected in gas pressure or volume change. Therefore, maintaining a consistent air temperature throughout a system would be a real advantage. Ideally, the temperature of intake air should be low, the temperature of the air should not increase during compression, and the compressed air dis- tributed to workstations should be near the air tempera- ture where the workstation is located, Figure 16-5. Air temperature relates to both the energy consumed by the prime mover and the water vapor brought into the system with the atmospheric air. Compressing air pro- duces heat. This increases the temperature and pressure of the air in the confi ned space of the pneumatic system. This warmed, compressed air retains the water vapor present in the atmospheric air brought into the compressor. Two conditions result when this warm, humid, high-pressure air cools as it moves through the sys- tem distribution lines. The fi rst of these conditions is a reduction in the pressure of the air as it cools. The amount of pressure reduction is based on the general gas law. The second condition relates to the dew point of the compressed air. As the temperature of the com- pressed air drops to the dew point, liquid water forms in system components and distribution lines. This liq- uid water can damage internal components and cause operating problems when a mixture of air and water is discharged at the distribution system outlets. accumulation of dirt in lines and sensing orifi ces of control valves. These conditions can quickly reduce the effi ciency of compressors and workstation circuits. The intake-line fi lter removes dust and dirt from atmospheric air before the air is allowed into the compres- sor inlet, Figure 16-4. The type of fi lter depends on atmo- spheric conditions, the size and type of compressor, and the fi nal use of the compressed air. Many different fi lter designs are used with pneumatic systems. However, fi l- ters can generally be placed in one of three categories: • Dry. • Oil wetted. • Oil bath. Dry fi lters are available in a large number of confi gu- rations using paper, plastic, cloth, ceramic, or metal ele- ments. The fi lter element remains dry as it traps dirt. Oil-wetted fi lters use metal-packed, woven wire or other material held in a metal frame. A light oil coat- ing is used on this material to trap the dust and dirt entering the fi lter. Atlas Copco Figure 16-4. An air filter in the compressor intake line is a first step in the production of clean compressed air. Pneumatic System Function Air Intake Air Compression Air Distribution and Use System Location System atmospheric air intake Compressor station Distribution lines and workstation Ideal Air Temperature Lowest ambient temperature available Minimal air temperature increase Near-ambient air temperature Goodheart-Willcox Publisher Figure 16-5. Ideally, air temperature should change little as it is processed from the system inlet to use at the workstation.