TM 1-1500-204-23-9 g. Air  Compressors.    Air  compressors,  shown  in figure   9-14,   are   portable   sources   of   compressed   air. They  are  self-contained  and  mounted  on  a  two  or  four wheel trailer frame. (1) Purpose.    An  air  compressor  is  designed to continuously deliver a rated volume of air at a rated pressure.  Depending upon the flow (rated in cubic feet per  minute  or  cfm)  and  the  pressure  (rated  in  pounds per  square  inch  or  psi),  an  air  compressor  provides  air for the following uses: ·  Operation     of     pneumatic     tools,     greasing equipment,    paint    spray    guns,    and    for    tire inflation. ·  Supply air to charge aircraft pneumatic systems, hydraulic   accumulators,   oleo   struts,   and   tires, and for servicing the trailers that will be used for these purposes. (2) Types.  Air compressors are typed by the maximum     flow     and     pressure     they     can     produce. Generally,  the  low  pressure  compressors  provide  up  to 175  psi  and  are  used  for  pneumatic  tools,  spray  guns, greasing  equipment,  and  so  forth.    The  high  pressure compressors  produce  pressures  of  3,000  to  3,500  psi. These are used for tasks such as charging accumulators, struts, and pneumatic systems on aircraft. The  external  appearance  of  types  may  vary  by  model number or manufacturer.  The air compressors shown in figure  9-14  are  typical  of  those  found  in  maintenance organizations. (3) Principles  of  operation.    Air  compressors have  a  gasoline  engine  which  drives  the  compressor, either by a belt or through a clutch.  The compressor has low  and  high  pressure  cylinders.    Air  is  drawn  into  the low pressure cylinder through the air filter and delivered to   the   high   pressure   cylinder   through   the   intercooler coils.    The  compressed  air  then  goes  through  a  check valve  to  the  receiver  tank.    The  check  valve  prevents back flow. (4) Safety   practices   and   procedures.      The following  special  precautions  should  be  observed  when using air compressors: ·  Do  not  use  low  pressure  hoses  (300  psi)  on  a high pressure compressor (3500 psi). ·  Do  not  use  the  air  compressor  in  an  enclosed area due to possible carbon monoxide poisoning. ·  Do  not  try  to  override  or  defeat  the  pressure relief valves. ·  Do not refuel the compressor when the engine is hot. ·  Leave all safety devices (e.g.  belt guard) in place. (5) Operating     procedures.          Consult     the applicable maintenance manual for the type and model air compressor being used for specific instructions.  The following general procedures pertain to the operation of the air compressor: (a) Locate    the    compressor    near    the work site. (b) Set the brake. (c) Open    the    siphon    valve    on    the receiver   and   close   the   shutoff   valve   on   the   control panel. (d) Start the engine. (e) When the pressure reaches operating pressure, open the shutoff valve. (f) Adjust the pressure as required and use the compressor. (g) For    shutdown,    close    the    shutoff valve and position the ignition switch to off. (h) When   the   engine   stops,   open   the siphon valve and drain the water accumulation. (6) Inspection. The following general operator inspections apply to air compressors.  Detailed inspection   requirements   are   found   in   the   applicable maintenance manual. (a) Liquid levels.  Check the engine and compressor  oil  levels,  gas  tank  fuel  level,  and  battery electrolyte level.  Service as needed. (b) Hand  or  parking  brake.    Check  for proper operation. (c) Hoses.      Look   for   wear   or   loose fittings. 9-40