TM 5-3895-374-24-2 MECHANICAL  OPERATION:    This  Low-High-Off  system  uses  a two-stage  Oil  Pump  (2)  with  an  internal  bypass  Oil  Nozzle  (14) (see note 1, page 20) in conjunction with Movable Air Dampers (4) to provide a  low  fire  start  and  a  high  fire  run  sequence.    A  direct spark oil ignition system will normally be supplied at firing rates up to  45  GPH,  with  a  spark  ignited  gas  pilot’  to  ignite  the  main  oil flame  above  that  point.    Certain  insurance  company  codes  will require  the  gas  pilot  system  on  lower  input  sizes.    Nozzle  supply pressure is set by adjusting the Oil Pump Pressure Regulator 'A” Allen wrench fitting (3).    Turn  clockwise  to  increase  the  pressure and  counter-clockwise  to  decrease  the  pressure  to  the  Nozzle. Nozzle  supply  pressure  is  taken  at  the  plugged  Pump  Nozzle Pressure Gauge Port (6).  Nozzle supply pressure will normally be approximately 300 PSI at both high and low firing rates.  Flow rate pressure  for  both  high  and  low  fire  is  taken  at  Bypass  Pressure Gauge Tee (15).  Low fire pressures are set by adjusting the low fire  Regulating  Valve  (8).    Turning  the  low  fire  Regulating  Valve adjustment nut clockwise will increase the pressure at the Bypass Pressure   Test   Tee   Gauge   (increasing   the   low   fire   input)   and counter    clockwise    will    reduce    the    pressure    at    the    gauge (decreasing the low fire input).  Low fire pressure will normally be in the 60 to 100 PSI range and at high fire in the 180 to 225 PSI range, but both pressures will vary according to the specific nozzle being  used,  as  well  as  job  conditions.    At  light  off,  the  Main  Oil Solenoid Valve (1) is energized, allowing fuel to flow to the Nozzle. At  the  same  instant  a  portion  of  the  oil  bypasses  the  Nozzle through   the   adjustable   low   fire   regulating   valve,   reducing   the pressure at the Nozzle as required for low fire rates.  When the low fire flame is proven by the flame detector', the Return Oil Solenoid Valve (7)  is  de-energized,  putting  full  high  fire  pump  pressure  on the Nozzle.  Simultaneously, the Three-Way Solenoid Valve (10) is energized,   allowing   oil   into   the   Hydraulic   Cylinder   (9)   which mechanically  drives  the  Air  Damper  Arm  (13)  to  the  high  fire position.    The  burner  operates  at  full  high  fire  until  the  system demand is satisfied.  Refer to page 30, Table 8 or page 31, Table 9 to  determine  nozzle  return  flow  pressure  and  flow  rates.    This depiction shows the Air Dampers and Hydraulic Cylinder at the low fire light off position. The Low-High-Low system is identical to the Low-High-Off system, except  that  an  additional  pressure  or  temperature  controller  is added   to   the   system,   which   at   a   selected   preset   point   will electrically switch the burner to either the high or low fire position.  When the burner is running at high fire and the controller calls for low fire, the normally closed Oil  Solenoid  Return  Valve  (7)  (closed  at  high  fire)  is  energized, reducing nozzle pressure to the low fire rate.  Simultaneously, the Three-Way  Solenoid  Valve  (10)  is  de-energized,  allowing  oil  to flow out of the Hydraulic Cylinder (9) back to the Pump and driving the Air  Dampers  (4)  to  the  low  fire  position.    Responding  to  load conditions,  the  burner  can  alternate  indefinitely  between  the  low and high fire positions without shutting down.  When system load demand  is  satisfied,  all  fuel  valves  are  de-energized  and  the  Air Dampers are placed in the light off position in preparation for the next  firing  cycle.    The  opening  distance  of  the  Air  Dampers  is controlled by positioning the Air Damper Drive Arm (13) relative to the Acorn Nut (16) mounted on the end of the Hydraulic Cylinder piston  rod.    The  maximum  travel  is  with  the  Damper  Drive  Arm positioned to be in contact with the hydraulic oil cylinder Acorn Nut at all times.  If less travel is desired set the Air Damper Drive Arm to allow a gap between it and the Acorn Nut.  (Depending on Air Damper positioning, it may be necessary to loosen its set screws to attain proper Air Damper opening distance.) The wider the gap (when the burner is off), the less the overall travel when going to the high fire position.  When setting the Drive Arm position, relative to  the  Acorn  Nut,  make  certain  that  the  Air  Dampers'  travel  is correct for proper combustion at all firing positions and that there is no binding of the Linkage or Dampers.  Make certain the cast iron Linkage Return Weight (5) is secure on its Air Damper Arm (17). * Not shown in this depiction.  See page 4, Fig.  2 Note 1 The   system   depicted   in   Fig.      23   uses   a Webster    Model    22R    oil    pump.        II    your system  uses  a  Suntec  H  model  pump,  the sequence of operation and the oil components     would     be     identical     to     the Webster 22R system. For additional information on your specific system refer to the   oil   piping   diagram   and   the   oil   pump manufacturer’s   bulletin   supplied   with   the burner. Note 2 Component     operational sequencing will vary    with    the    specific    Flame    Safeguard Control  being  used.    Refer  to  the  specific Flame  Safeguard  Control  bulletin   supplied with the burner for complete Information. (page 3-969)