TM 5-3895-374-24-2 Table 11 Pilot Orifice Schedule DRILL SIZE BURNER NATURAL PROPANE MODEL GAS GAS C1-G(O) Standard 6” Fan #36 #48 Optional 7x3 or 7-5/8x3-1/2 Fan #30 #48 C2-G(O) Standard 7x3 Fan #36 #48 Standard 7-5/8x3-1/2 Fan #36 #48 Optional 8-3/8x3-1/2 Fan #36 #48 DRILL SIZE BURNER NATURAL PROPANE MODEL GAS GAS C3-G(O) Standard 8-3/8x3-1/2 Fan #30 #48 Optional 9x4 Fan #30 #48 C4-G(O) Standard 8-3/8x4-1/2 Fan Standard 9x4 or 9x5-1/2 Fan  #30 #48 C5-G(O) Standard 10 3/4x 5-1/2 Fan #30 #48 C5-G(O)•B Standard 10 3/4 x 5 1/2 Fan    None #19 C6-G(O) Standard 10 3/4 x 5 1/2 Fan    None #19 Gas Pilot Ignition Adjustment Excessive  gas  pressure  and  insufficient  air  may  be  the  most common    causes    of    pilot    ignition    failure.        Burners    with automatic   air   dampers   linked   to   the   gas   valve   or   damper motor should have pilot gas pressures as follows: C1-0 (Gas Pilot)  C1-GO-10, C1-GO-12 With Std.  #36 Orifice 2 ½” - 3 ½” W.C. With 7” Fan & #30 Pilot Orifice 1 ½” - 2 ½” W.C. C2-OA   (Gas Pilot) C2-G(O)-15 2” - 4” W.C. C2-OB   (Gas Pilot) C2-G(O)-2OA(B) 1 ½” - 3” W.C. C3-O (Gas Pilot) C3-G(O)-20, C3-G(O)-25 1 ½ “-2” W.C. C4-O (Gas Pilot) C4-G(O)-25, C4-G(O)-30 1 ½”- 2”W.C. C5-O (Gas Pilot) C5-G(O)-30, C5-G(O)-30B   1 ½” - 2” W.C. C6-O (Gas Pilot) C6-G(O)-30 1 ½” - 3” W.C. Fixed fired (on-off) burners with manually adjustable dampers may need  slightly  higher  pressures,  but  in  any  event  do  not  increase pressure  beyond  that  required  for  a  stable  flame  signal.    Gas pressure should be read at the test tee on the pilot gas supply pipe with a manometer or 0-10” w.c.  gauge.  Look for stability of gas pressure  at  all  times.    For  burners  equipped  with  automatic  air dampers  (linked  to  the  gas  valve  or  damper  motor),  there  is  a tendency to set the air dampers in a closed, barely open position. This   action   may   produce   insufficient   air   for   dependable   pilot ignition.    Air  damper  openings  should  be  at  least  1/1”  on  each damper  or  1/2”  on  one,  with  the  other  nearly  closed.    Some  job conditions   or   heat   exchangers   may   require   larger   air   damper openings or different gas pressures than those shown above.  For dependable pilot ignition, always use air damper setting to provide MOST  air  and  LOWEST  pilot  gas  pressure  setting  allowable  for good  pilot  signal  at  all  times.    On  fixed  fire  (on-off)  burners  the manually  adjustable  air  damper  setting  will  need  to  match  air  for proper CO2 setting.  The following steps should be taken: 1. Remove pilot assembly and check for proper orifice size (the  orifice  size  is  stamped  into  the  hex  brass  fitting connected to the pilot head nozzle assembly) and spark gap.    The  spark  gap  between  the  electrode  and  the outside radius of the gas pilot assembly should be 1116” 3132”.    Do  not  set  spark  to  arc  against  the  pilot  head nozzle.  See Figures 35 and 36. 2. Close  checking  cock  (test  cock).    Start  up  burner  and stop  flame  safeguard  control  timer  with  “check”  switch during pilot ignition.  Access to “check” switch on Fireye D  Series  is  best  obtained  by  using  a  small  right  angle tool,  such  as  an  Allen  Wrench.    If  there  is  no  check switch, disconnect wire which energizes main automatic gas valve, so that air damper is not actuated. 3. Observe pilot signal with DC voltmeter or microammeter and reduce pilot gas pressure to a point where the signal is erratic or reduced substantially from initial reading. 4. Raise the pilot gas pressure to the point where the signal is  again  stable.    Remove  scanner  and  use  a  mirror  to view  the  pilot  flame  through  the  scanner  pipe  (a  live flame   from   cigarette   lighter   or   butane   torch   may   be needed  to  keep  scanner  actuated).    Be  sure  to  get  full coverage of scanner pipe by pilot flame. Release “check” switch or reconnect main automatic gas valve (see step #2) and observe meter as main gas valve opens and moves air damper. If there is a drop in signal as  this  happens,  increase  pilot  pressure   slightly   until signal is steady at all times. Refer  to  page  35,  “Gas  Pilot  Flood  Test”  as  another means of determining proper pilot fuel/air mixture. Figure 34 (page 3-986)