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MECHANICAL OPERATION OF FUEL/AIR CONTROL MODES
Typical Oil Burner with On-Oil Fuel/Air Control Mode

TM-5-3895-374-24-2 M081 Asphalt Mixing Plant Manual
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TM 5-3895-374-24-2 Figure 19 Typical Gas Burner with Low-High-Off or Low-High-Low Fuel/Air Control Mode (Model C-G) MECHANICAL   OPERATION:   The   Low-High-Off   system   uses   a Motorized  Gas  Valve  (1)  to  control  the  Low-High-Off  operation  of gas to the Firing Head (2), as well as movable Air Dampers (3) by means  of  the  mechanical  Linkage  (4).    Gas  flow  control  rate  is accomplished by adjustment of the Main Gas  Pressure  Regulator (5)  and  by  a  Limiting  Orifice  (when  installed)  located  in  the  Side Orifice  Tee  fitting  (7)  at  the  inlet  piping  to  the  gas  manifold.    A proven spark ignited gas pilot’ provides ignition for the main flame. When   the   gas   pilot’   has   been   proven   by   the   flame   detector (scanner)’,  the  Motorized  Gas  Valve  begins  to  open,  allowing  a controlled fuel/lair mixture to the Firing Head for low fire light off - and continues to open, increasing the fuel/air flow until the high fire position    has    been    reached.        Firing    head    gas    pressure    are measured  at  the  1/4“  plugged  Gauge  Test  Port  (8)  in  the  Side Orifice   Tee.      Refer   to   page   33,   Table   10   for   orifice   sizing information.  The burner operates at high fire until the system load demand is satisfied, at which time the Motorized Gas Valve closes and  the  Air  Dampers   are   returned   to   the   light   off   position   in preparation for the next operating cycle.  This depiction shows the Linkage in the low fire start position.  The Low-High-Low system is identical  to  the  Low-High-Off  system  except  that  -  the  Motorized Gas  Valve  (1)  has  a  Low  Fire  Operating  Position  Adjustment  in addition  to  the  light  off  and  high  fire  operating  positions.    (See manufacturer's bulletin included with the burner.) An  additional  temperature  or  pressure  controller  is  added  to  the system, which at a selected preset point will electrically switch the Motorized Gas Valve and Air Dampers (3) to either the low fire or the   high   fire   position,   as   the   system   load   demand   requires. Depending  on  system  load  conditions,  the  burner  can  alternate indefinitely  between  the  low  and  the  high  fire  positions  without shutting   down.      When   the   system   demand   is   satisfied,   the Motorized Gas Valve closes (normally the burner will be in the low fire position at this time) and the Air Dampers are returned to the light off position, in preparation for the next operating cycle.  The river Arm (10) connected to the Motorized Gas  Valve will increase the travel of the Air Damper Arm (13) as the Linkage Rod ball joint (11)  is  moved  away  from  the  Gas  Valve  Crank  Shaft  (12).    The travel  of  the  Air  Damper  Driven  Arm  will  be  increased  as  the Linkage Rod ball joint (14) is moved toward  the  Air  Damper  Axle Shaft  (15).    When  adjusting  linkage  travel,  make  certain  that  the driven arm Linkage Return Iron Weight (16) does not interfere with the  Linkage  operation  -  and  that  all  linkage  components  are  free from binding. *Not shown in this depiction.  See page 4, Fig.  2. Note 1 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. Figure 20 Typical Gas Burner with Full Modulation Fuel/Air Control Mode (Model C-G) MECHANICAL OPERATION: This Full Modulation system uses a Diaphragm  (1)  or  Motorized  Gas  Valve  to  ensure  opening  and positive  closure  of  the  gas  source  to  the  Firing  Head  (2).    A Modulating Motor (3) controls the positioning of a Butterfly Gas Proportioning  Valve  (4)  and  movable  Air  Dampers  (5)  through Mechanical Linkage (6).  The gas flow control rate Is accomplished through  adjustment  of  the  Main  Gas  Pressure  Regulator  (71  and the Butterfly (page 3-966)







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