a single bundle of tubes enclosed in a cylindrical shell. The air to be cooled passes through the tubes while the water  circulates  around  the  outside  of  the  tubes absorbing the heat from’ the compressed air. The baffles are used to direct the water flow across the heat exchanger tubes in the most efficient manner. The intercooler  is  located  between  the  discharge  of  one cylinder and the intake of the next cylinder on a multistage  compressor.    The intercooler reduces the temperature and volume of the compressed air for delivery  to  the  next  compression  stage.  The  aftercooler is located at the discharge of the last cylinder to cool the air, to reduce the volume, and to liquify any condensable vapors. AIR RECEIVERS.—The  receiver  is  nothing more than a tank designed to hold the -air that is compressed to meet supply peak demands that are in excess of the compressor capacity. Additionally, receivers  function  as  pulsation  dampers  on  reci- procating compressor installations. Figure 6-47 shows an air receiver. SEPARATORS.—Separators   remove   oil   and water  from  compressed  air.  Figure  6-45  shows  a centrifugal moisture separator. The air enters the unit in  a  swir  ling  motion.  Centrifugal  action  forces  the moisture to the walls of the separator and then the moisture drains to the bottom of the separator. Another type of separator is the baffle type. This separator causes the air entering the separator to make sudden changes in direction, causing the heavier moisture particles to strike the baffles and walls and drain to the bottom. TRAPS.—Compressor plant traps drain moisture from intercoolers, aftercoolers, receivers, and distribution piping. Common traps used are the ball  float,  the  bucket,  and  the  inverted  bucket  traps (fig. 6-46). DRYERS.—Dryers    remove    moisture    from compressed air that would condense in air lines, air tools, and pneumatic instruments. Condensation can cause damage to equipment by corrosion, freezing, and water  hammer,  and  will  cause  instruments  to malfunction. The three types of dryers are adsorption, deliquescent, and refrigeration. The adsorptive dryer is made of some type of desiccant, such as silica gel or activated alumina. The desiccant adsorbs and holds the water vapor from the air. Adsorption-type dryers (fig. 6-48) consist of two drying towers, each containing an adsorbent, plumed in parallel. The drying towers are cycled manually or automatically, so one tower is on stream and the other tower is being reactivated. Reactivation is accom- plished by heating the desiccant which drives the moisture out to waste. Only one type of dryer was discussed in this chapter.   Other   types   of   dryers,   maintenance, operation  of  controls,  and  other  interesting information  about  compressors  can  be  found  in NAVFAC  MO-206,  Maintenance and Operation of Compressor  Plants. SAFETY PRECAUTIONS Listed below are some safety tips on how you can avoid air compressor accidents. Keep the hose connections on portable air compressors tight, and inspect these connections often  to  ensure  they  remain  tight. Check the safety valves and gauges frequently to make sure they are working correctly. Use fixed tow bars, not chains or ropes, when moving portable air compressors. Check the wheels of portable air compressor carriages to ensure proper operation. When an air compressor is started, check the safety valves, the pressure controls, and the regulators to determine that they are working properly. DO  NOT  leave  the  area  of  an  operating compressor unless you are sure that the control, Figure 6-45.—Centrifugal moisture separator. 6-51