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MECHANICAL  OPERATION
Figure 25 Typical Oil Burner with Full Modulation Fuel/Air Control

TM-5-3895-374-24-2 M081 Asphalt Mixing Plant Manual
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TM 5-3895-374-24-2 Figure 24 Typical Oil Burner with Low-High-Off or Low-High-Low Fuel/Air Control Mode Using a Two-Step Oil Pump.  (Model C-0) MECHANICAL  OPERATION:    This  Low-High-Off  system  uses  a Two-Step  Oil  Pump  with  a  simplex  Oil  Nozzle  (14)  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, but certain insurance company codes could require a spark  ignited  gas  pilot  to  provide  ignition  for  the  main  oil  flame. Nozzle  flow  rate  pressure  is  taken  at  the  118”  Plugged  Pump Pressure Gauge Port (6).  The low fire oil rate is set by adjusting the  Oil  Pump  Low  Pressure  Regulator  (8).    The  high  fire  oil  flow rate is set by adjusting the Oil Pump High Pressure Regulator (3). For both high and low fires turn the adjustment screws clockwise to  increase  the  pressure  and  counterclockwise  to  decrease  the pressure to the Nozzle.  Approximate low fire oil pressures are 100 to 125 psig and high fire, 200 to 300 psig.  Both settings will vary depending   upon   the   specific    nozzle    size    selected    and    job conditions.    See  pages  30-31,  Tables  8  &  9  for  specific  nozzle pressures and flow rates.  At light off the Main Oil Solenoid Valve (1)  is  energized,  allowing  fuel  to  the  Nozzle.    A  normally  open pump mounted Oil Solenoid Valve (7) allows a controlled flow of oil to the Nozzle in accordance with the pressure setting of the pump low  fire  adjustment.    When  the  low  fire  flame  is  proven  by  the flame detector*, the pump mounted, normally open Solenoid Valve is  energized  (closes),  putting  full  high  fire  pump  pressure  on  the nozzle.  Simultaneously, the Three-Way Solenoid Valve (10) is energized, allowing oil into the Hydraulic Oil Cylinder (9) which mechanically drives the Air Damper Arm (13) to the  high  fire  open  position.    The  burner  operates  at  full  high  fire until the system demand is satisfied.  This depiction shows the Air Dampers   and   the   Hydraulic   Cylinder   at   the   low   fire   light   off position. The   Low-High-Low   systems   are   identical   to   the   Low-High-Off system,    except    that    an    additional    temperature    or    pressure controller is added to the system.  At a selected preset point, it will electrically  switch  the  Oil  Valves  and  Air  Damper  components  to place the firing rate either in the low or the high fire run position. When the burner is running at high fire and the controller calls for low  fire,  the  normally  open  pump  mounted  Solenoid  Valve  (7) (which  is  closed  at  high  fire)  is  de-energized  (opens),  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  back  to  the  Pump  (2)  and  driving  the  Air Dampers   (4)   to   the   low   fire   position.      Depending   on   load conditions,  the  burner  can  alternate  indefinitely  between  the  low and the high fire positions, without shutting down.  When  system demand  is  satisfied  all  fuel  valves  are  de-energized  and  the  Air Dampers are  placed  in  the  light  off  position  for  the  next  start  up. The Air Damper position for low fire run and light off position are one and the same in this system.  The opening distance of (page 3-970)







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