SECTION IV. OPERATION INSTRUCTION 4-1. GENERAL.  This section describes the theory of operation,     operating     procedure,     and     the     operating controls and indicators for the air compressor unit.  The air  compressor  unit  is  designed  to  deliver  contaminant free, dry breathable air under pressure up to a maximum of 3,200 psig (22,048 kPa) at a rate of 20 cfm.  Air supply cylinders, 3500 psig (24115 kPa) may be serviced by the air compressor unit. 4-2. THEORY  OF  OPERATION.    The  reciprocating air   compressor   assembly   is   connected   to   the   diesel engine  power  source  by  means  of  a  manually  operated clutch.    Normal  operating  speed  of  the  diesel  engine  is 2150   RPM.      In   the   air   compressor   assembly,   air   is compressed   to   the   desired   pressure   in   four   separate stages.    The  engine  speed  is  controlled  manually  and protected by the internal engine governor control. 4-3. AIR  COMPRESSING  MODE  (Figure  4-1).    As the first compression stage piston travels downward, the pressure  differential  causes  the  first  compression  stage intake  valve  to  open,  drawing  air  from  the  atmosphere through   a   dry   element   type   air   cleaner   into   the   first compression  stage  cylinder.    As  the  first  stage  piston travels  upward  the  intake  valve  closes  allowing  the  air trapped in the cylinder to be compressed to a pressure of 55  ±  5  psig  (379  ±  34.5  kPa).    This  air  then  passes through  the  first  stage  air  cooler  subassembly  and  the first stage trap which reduces the air temperature due to compression heat and removes oil and condensate prior to   the   air   entering   the   second   compression   stage cylinder.  As the second compression stage piston starts to travel downward, the pressure differential causes the second stage intake valve to open, admitting the air from the  first  stage  air  cooler  subassembly  into  the  second compressor  stage  cylinder.    When  the  second  stage piston  starts  to  travel  upward;  the  second  stage  intake valve closes, allowing the air trapped in the cylinder to be compressed to a pressure of 195 ± 10 psig (1344 ± 68.9 kPa).  This air then passes through the second stage air cooler  subassembly  and  second  stage  trap  for  cooling and   removal   of   oil   and   condensate   prior   to   the   air entering  the  third  stage  compression  cylinder.    As  the third compression stage piston starts to travel downward, the  pressure  differential  causes  the  third  stage  intake valve to open admitting the air from the second stage air cooler subassembly.  When the third stage piston starts to  travel  upward,  the  third  stage  intake  valve  closes, allowing the air trapped in the cylinder to be compressed to a pressure of 900 ± 50 psig (6201 ± 344.5 kPa).  This air   then   passes   through   the   third   stage   air   cooler subassembly and  third  stage  trap  for  cooling  and  removal  of  oil  and condensate   prior   to   entering   the   fourth   compression stage cylinder.  As the fourth stage piston starts to travel downward,  the  pressure  differential  causes  the  fourth stage intake valve to open admitting the air from the third stage  air  cooler  subassembly.    When  the  fourth  stage piston  starts  to  travel  upward,  the  fourth  stage  intake valve closes allowing the air trapped in the cylinder to be compressed to a pressure of 3,200 ± 25 psig (22,048 ± 172.3  kPa).    This  air  then  passes  through  the  fourth stage    air    cooler    subassembly    which    reduces    the temperature of the air.  The air then passes through the mechanical  filter  where  airborne  foreign  particles  and moisture are removed.  The partially clean air is  then  directed  through  the  rupture  disc  (4,400  psi)  to the first (No.  1) dehydrator then to the second (No.  2) dehydrator,    where    the    air    is    thoroughly    dried    of condensate and oil. 4-4. Attached   to   dehydrator   (Cyl.      No.      2)   is   the priority valve which maintains correct pressure for proper circulation   within   the   air   purification   cylinders.      The priority valve is set to open at  2,300  psig  (15,897  kPa). From  the  priority  valve  the  air  passes  through  the  air purification   cylinders   before   it   flows   through   the   ten micron   filter   where   airborne   particles   larger   than   ten microns are removed. 4-5. A  method  of continuous  removal  of moisture collected  in  the  first,  second,  and  third  stage  traps  is provided.    Removing  this  moisture,  as  it  is  separated, allows the compressor to operate for an extended period of  time  without  unloading.    The  air  allowed  to  bleed-off will  not  appreciably  reduce  the  pressure  of  the  output service  air,  but  it  will  result  in  a  slight  increase  in  the pressure   of   the   first   stage   air.      The   first   stage   trap continuous  bleed  valve  generates  a  one  psi  pressure differential   across   the   valve   orifice.      This   differential allows the bleed valve to crack, allowing a small amount of the moisture laden pressurized air to bleed off through the   first    stage    trap    filter    and    line    strainer    to    the condensate receiver.  As pressurized air from the second stage  compression  cylinder  passes  through  the  second stage   trap   it   generates   a   pressure   differential   in   the second stage trap continuous bleed valve, 195 ± 10 psig (1344 ± 68.9 kPa) downstream of the valve and 14.7 psi (101.3  kPa)  upstream  of  the  valve.    The  second  stage continuous bleed valve will open, causing the first stage trap  continuous  bleed  valve  to  open.    This  will  allow  a small amount of moisture laden, pressurized air to bleed off through the second stage trap filter, second stage line 4-1