TM 5-3895-374-24-2 temperature or pressure controller will now modulate the firing rate to match the load demand of the system, while maintaining proper fuel/air    ratios.        Prior    to    reaching    the    system    pressure    or temperature operating control cut off point, the burner should be at or  near  the  low  fire  operating  position.    At  the  end  of  the  firing cycle,  the  normally  closed  Oil  Valve  will  be  de-energized  and  the Modulating  Motor  will  position  the  Air  Dampers  and  Modulating Valve to the low fire position, ready for the next start up sequence. This depiction shows the Linkage in the low fire light off position. See page 21, Fig.  28 for linkage adjustment information.  Also see this  page,  Fig.    27  for  information  on  the  Varicam^TM  modulating characterized fuel metering sytsem. *Not shown in this depiction.  See page 4, Fig.  3. Note 1 Some   modulating   Low-High-Off   and   Low- High-Low    burners    will    be    supplied    with simplex, rather than internal bypass type, oil nozzles.    The  mechanical  operation  of  the simplex   nozzle   system   is   essentially   the same as the internal bypass system - except that  low  fire  oil  pressures  should  be  set  at 100 to 125 psig (adjust to suit job conditions)   and   high   fire   oil   pressures   at 280   to   300   psig   at   the   oil   pump   nozzle pressure   gauge   test   port.      Refer   to   the Burner Specification sheet shipped with the burner and/or page 31, Table 9  for  high  fire oil pressures and flow rates. The    oil    pump    depicted    in    the    oil    flow schematic   above   is   as    manufactured    by Webster Electric Company Inc.  If the pump on  your  burner  is  not  Webster,  refer  to  the oil  pump  bulletin  shipped  with  the  burner for   specific   adjustment   information.      Also see page 11, Fig.  11. 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. Figure 26 Gas or Gas/Oil Burner Fuel/Air Premix Adjustment - Oil, or Gas/Oil Burner Diffuser Adjustment FUEL AIR PREMIX ADJUSTMENT (OPTIONAL) The    adjustable    premix    blast    tube    (optional)    incorporates    an adjustable gas/air premix within the burner firing head.  The premix configuration is primarily used for cylindrical combustion chambers or high heat release pressurized fireboxes.  Moving the adjustment knob  back  increases  the  premix  air;  moving  it  forward  decreases the premix air.  Generally, the best (quietest/smoothest) operation is in the full forward position with minimum premix air.  The premix adjustment  is  set  at  the  factory  in  the  full  forward  position.    To attain   the   best   combustion   results   for   specific   job   conditions, change position in small increments. DIFFUSER ADJUSTMENT Moving  the  blast  tube  diffuser  assembly  fore  or  aft  on  gas  or  oil firing will move the flame front (point of retention) in order to attain the best (quietest/smoothest) combustion for specific job conditions.    If  the  initial   midway   point   factory   setting   does   not provide satisfactory results, move fore or aft in small increments to achieve  the  best  combustion  results.    If  unit  is  oil  or  combination gas/oil, the attached, flexible copper oil nozzle  line  will  move  fore or aft with the assembly.  When firing on oil, moving the assembly forward will tend to broaden the flame pattern and moving it back will narrow the flame pattern.  Similar results are obtained on gas, but   observation   of   sound   and   combustion   tests   are   the   best determinants of results on either gas or oil. Figure 27 Gas/Oil · Detail and Adjustments on Modulating Varicam^TM Characterized Fuel Metering System. (page 3 - 972)