ENGINEMAN  1  &  C aid  in  keeping  the  air  supply  clean,  filters  are fitted to compressor intakes. Unless inspected and cleaned regularly, these filters become clogged and cause a loss of capacity. Filter elements should be removed from the intake and cleaned either with a jet of hot water or steam, or by immersion in a strong solution of sal soda. The filter body should be drained and replaced. Filter elements of the oil-wetted type should be dipped in a clean, medium viscosity oil after  cleaning  and  the  excess  oil  should  be drained from the elements before replacing them on the filter intakes. Gasoline or kerosene should not be used for cleaning air filters because of the explosive fumes which may collect in the com- pressor or air receiver. Dehydrators On some ships, compressed air is used for the operation of missile system components and with automatic controls for boilers. In order to pre- vent   failure   of   these   systems,   moisture   and lubricants from the compressor must be kept at a   minimum.   Blowing  down  the  compressor separators prevents most of this, but still some moisture is carried over. To  aid  in  the  removal  of  the  moisture  and lubricants, two types of dehydrators are gener- ally used: type I refrigerant dehydrators and type II dehydrators using a desiccant of either silica gel  or  activated  alumina,  and  containing  electric heating  coils  for  reactivating  the  desiccant  when it  becomes  saturated  with  moisture.  Type  II dehydrators are normally installed in pairs so that one can always be in service while the other is be- ing  reactivated. Air Valves Air inlet and discharge valves are vital parts of a compressor and should receive careful atten- tion.  When  these  valves  leak,  the  compressor capacity  is  reduced  and  results  in  an  unbalanced stage  pressure. There are several symptoms which signify that an air valve is not functioning properly. A devia- tion  from  normal  intercooler  pressure  may indicate a leaking or broken valve. A defective inlet valve above the intercooler will cause a rise in pressure in the intercooler, while a defective 7-2 discharge  valve  below  the  intercooler  will  cause a decrease in the intercooler pressure. An unusu- ally hot valve cover is a sign of valve trouble. Dirt  is  generally  the  cause  of  leaking  valves. The source of valve trouble can usually be traced to dirty intake air; the use of excessive or improper cylinder  oil;  or  excessively  high  air  temperature, resulting  from  faulty  cooling.  A  periodic  inspec- tion and cleaning of valves and valve passages will minimize  and  perhaps  prevent  the  occurrence  of air  valve  troubles.  The  frequency  for  cleaning valves  must  be  determined  for  each  installation. The air valves are easily accessible and are removed by first loosening the valve cover plates. Then the valve and valve unloader, if installed, may be lifted out. Each valve should be marked so that it may later be returned to the same open- ing from which it was removed. Dirt or carbon can usually be removed from valve parts without disassembling the valve. If disassembly  is  necessary,  notice  should  be  taken on how the various parts are arranged so that the proper relationship will be kept when the valve is  reassembled.  To  remove  carbon  from  valve parts,  soak  each  part  in  kerosene  and  then  brush or  scrape  lightly.  After  drying  and  reassembling the valve parts, test the valve action to be sure that the valve opens and closes freely. Before air valves are replaced in a cylinder, inspect the gaskets. If the gaskets are made of materials other than copper, and are damaged, change them. Copper gaskets should always be replaced.  Since  it  is  often  difficult  to  distinguish between suction and discharge valves, use extreme care when inserting valves in the cylinder. Make sure  that  suction  valves  open  TOWARD,  and discharge valves AWAY FROM, the center of the cylinder. Otherwise, serious damage or loss of capacity will result. If special locknuts are not pro- vided to seal against leakage at the threads of the valve setscrew, place a turn of solder or fuse wire around the screw and set down into a recess by the locking nut. Cylinders  and  Pistons When  you  find  that  it  is  necessary  to  inspect the cylinders or pistons of an air compressor, you should  refer  to  the  manufacturer’s  instruction manual and the appropriate Planned Maintenance System  (PMS)  maintenance  requirement  card