intake silencer. Some compressors are equipped with combination filter-silencer units that have the filter elements contained within the silencer housing.

Intercoolers

When air is compressed to 100 psi without heat loss, the final temperature is about 485F. The increase in temperature raises the pressure of the air under compression, thus necessitating an increase in work to compress the air. After the air is discharged into the receiver tank and lines, the temperature falls rapidly to near that of the surrounding atmosphere, thereby losing part of the energy generated during compression. The ideal compressor would compress the air at a constant temperature, but this is not possible. In multistage compressors, the work of compressing is divided between two or more stages, depending on the final discharge pressure required. An INTERCOOLER is used between the stages to reduce the temperature of compression from each stage. Theoretically, the intercooler should be of sufficient capacity to reduce the temperature between stages to that of the low-pressure cylinder intake. Actually, intercooling has three purposes: to increase compressor efficiency, to prevent excessive temperatures within the compressor cylinders, and to condense out moisture from the air.

Most intercoolers are either the shell and tube, air-to-water heat exchangers or the air-cooled radiator-type heat exchangers. Figure 11-12 illustrates a typical water-cooled inter-cooler. The air-cooled type is shown in figure 11-3.

Aftercoolers

Moisture carried in air transmission lines is undesirable because it causes damage to air- operated tools and devices. AFTERCOOLERS are installed in compressor discharge lines to lower the air discharge temperature, thus condensing the moisture and allowing it to be removed. Also, the cooling effect allows the use of smaller discharge piping. A water-cooled aftercooler is illustrated in figure 11-13.

Figure 11-12. - Typical water-cooled intercooler.