TM 5-3895-374-24-2 SECTION III REGULATION TYPES OF REGULATION (See Wiring Diagrams on page 24) The Model 7100 and 3000 Package Compressors are supplied  with  Dual  Control  Regulation,  and  the  Model  7100 and   3000   Bare   Compressors   are   supplied   with    Constant Speed Control Regulation. Dual   Control   is   accomplished   by   a   combination   of Auto-Star  t  And-Stop  Control  Regulation  which  consists  of  a pressure switch that makes or breaks the electrical contacts to the  motor  at  a  predetermined  pressure  setting,  and  Constant Speed Control Regulation which unloads the compressor at a predetermined  pressure  setting  while  the  motor  continues  to run AUTOMATIC START AND STOP CONTROL This type of regulation is  used  when  the  demand  for air   is   small   or   intermittent,   but   where   pressure   must   be continuously maintained. Automatic   Start   and   Stop   Control   is   obtained   by means   of   a   pressure   switch   which   makes   or   breaks   an electrical    circuit,    starting    and    stopping    the    driving    motor, thereby  maintaining  the  air  receiver  pressure  within  definite limits.The   pressure   switch   is   piped   to   the   receiver   and   is actuated by changes in air receiver pressure. Automatic  Start  and  Stop  should  only  be  used  when motor starts no more than 6-8 times per hour. CONSTANT SPEED CONTROL This type of regulation is  used  when  the  demand  for air is practically constant at the capacity of the compressor. Constant  Speed  Control  is  obtained  by  means  of  an auxiliary    valve    that    controls    the    operation    of    the    Inlet Unloaders,  thereby  loading  and  unloading  the  compressor  in accordance  with  air  receiver  pressure.    This  action  maintains receiver  pressure  within  definite  limits  while  the  compressor continues to operate. The  auxiliary  valve  is  piped  directly  to  the  receiver (See Figure 3-4) When  receiver  pressure  reaches  the  pre-set  unload pressure the auxiliary valve actuates and compressed air from the receiver     activates     the     inlet     unloader     piston.      This compressed  air  forces  the  unloader  piston  against  the  intake air  seat  in  the  unloader  which  blocks  the  flow  of  intake  air, through the filter/silencer. When   receiver   pressure   falls   to   the   pre-set   load pressure,  the  auxiliary  valve  closes,  shutting  off  pressure  to the unloader    vacuum within the inlet port retracts the piston. The air inlet opens and the compressor reloads. DUAL CONTROL Dual Control is accomplished by adjusting the lockout knob on the  top  of  the  auxiliary  valve.    See  Figure  3-3  For constant speed operation, turn the knob counterclockwise until fully  open.    This  adjustment  will  allow  the  valve  to  function. Turning the knob clockwise locks-out operation of the auxiliary valve.        Note-the    pressure    gauge    reading    at    which    the compressor cuts-out and re-establish this point if necessary. For  proper  dual  control  operation,  the  cut-out  setting of the pressure switch must be at least 5 PSIG ( 35 kg/cm2) greater than the cutout pressure of the auxiliary valve Figure 3-1 Typical Dual Control arrangement. PRESSURE SWITCH ADJUSTMENT The pressure switch has a Range Adjustment and a Differential    Adjustment.        See    Figure    3-2.        The    Cut-out (Compressor  Shutdown)  is  the  pressure  at  which  the  switch contacts   open,   and   the   Cut-in   (Compressor   Restart)   is   the pressure at which the switch contacts close. The  cut-out  point  may  be  increased  by  screwing  the range adjustment  clockwise.    Screwing  the  range  adjustment counterclockwise    decreases    the    cut-out    point.        Note    the pressure  gauge  reading  at  which  the  compressor  cuts-in  and out and re-establish pressure setting if necessary. The    differential    pressure    may    be    increased    by screwing the differential adjustment clockwise.  Backing off the differential adjustment will narrow the span.  It is advisable to have   as   wide   a   differential   as   possible   to   avoid   frequent starting  and  stopping  of  the  compressor.    Note  the  pressure gauge   reading   at   which   the   compressors   cuts-out   and   re- establish this point if necessary. There is interaction between these two adjustments, if the cut-out is increased, the differential will also increase, or, if the  differential  is  narrowed,  the  cut-out  will  be  reduced,  etc. These  factors  must  be  considered  when  adjusting  the  switch and compensate for accordingly. Figure 3-2.  Typical pressure switch cut-in and cut-out adjustment. page 3- 834