Underground piping is normally placed as direct burial. Because this type of placement generally lowers the temperature of the air in the piping, more condensation will form within the pipe than in an aboveground system. The provisions to remove the condensation may be building basement drip legs, or manholes may be required. If the soil is corrosive, cathodic protection may be needed. Underground lines are pitched the same as aboveground lines at 3 inches per 100 feet; however, drip legs differ from aboveground lines in that belowground lines require a drip leg at not over 500 feet. Insulation on buried compressed air piping should be shop-coated, wrapped, tested, and handled according to the NAVFAC specification 34-Y, Bituminous Coating for Steel Surfaces.
Air filters are provided on compressor intakes to prevent atmospheric dust from entering the compressor and causing scoring and excessive wear. Two types of air filters are used-the dry type and the oil-wetted type. Generally, the dry-type filter is more efficient than the oil-wetted type in trapping and removing very fine, solid particles from the incoming air; however, dry-type filters require cleaning and replacement more often than the oil-wetted types. Oil- wetted types are usually used under very dusty, dirty atmospheric conditions.
SILENCERS.-Air compressors are fitted with silencers (fig. 6-43) that are sound-absorbing devices attached at the intake and output of the compressor. In general, air noise silencers are cylindrical housings containing acoustically tuned baffles and sound- absorbing material.
INTERCOOLERS AND AFTERCOOLERS. - Intercoolers and aftercoolers are used to reduce the heat buildup due to the compression of air. The two mediums used are water and air. Normally air is used on smaller compressors. The air-cooled heat exchanger is simply a set of fins and/or tubular radiator. No liquid of any sort is used for cooling. The water-cooled heat exchanger operates as a shell and tube design (fig. 6-44). The tubes commonly consist of
Figure 6-43. - Compressor intake silencer.
Figure 6-44. - Water-cooled heat exchanger.Continue Reading