TM 5-3895-374-24-2
Pilot Spark Ignition Electrode Adjustment
The arc from the electrode tip should jump from the tip to the body
of pilot housing and should be lined up with the hole in the
backside of pilot housing, so that the blower air passing through
this hole will cause the arc to “flag” or move around. Normal spark
gap should be 1/16” - 3/32”. Electrode should not be moved so far
forward that the pilot flame will impinge on the porcelain insulator.
This condition will cause the porcelain to crack and break off at the
point of flame impingement.
Figure 35
Figure 36
C3, C4 & C5 Ignition Electrode Adjustment
Gas Pilot Flood Test
Many pilot problems are caused by a poor mixture of gas and
air at the point of ignition (ignition spark gap). The cause of
this poor mixture condition is usually excessive gas flow or
insufficient air (air dampers are closed too far).
Once the pilot is adjusted and felt to be correct it is suggested that
the following test be accomplished to further verify that the pilot will
be reliable.
1.
Turn the burner off and shut the manual leak test cock in
the main gas train. (This valve should always be closed
when making pilot adjustments.)
2.
If the burner is Low/High/Off, Low/High/Low or
Modulating, take steps to keep the fuel air linkage in the
pilot light off position. If the flame safeguard control has
a timer “check” switch, it can be placed in the test
position. If the flame safeguard control does not have
the timer switch, it may be necessary to disconnect the
power wire to the motorized gas valve.
3.
Install a 0 to 10” W.C. gas pressure gauge or a
manometer in the pilot test tee fitting. Plug an
appropriate flame signal meter into the flame safeguard
control.
4.
Disconnect the high tension ignition leadwire at the
ignition transformer secondary terminal. Either hold onto
the insulated portion or let the free ignition wire hang
loose, so that it is not able to come into contact with the
bare ignition terminal on the transformer.
5.
Start the burner and let it go through the prepurge period.
As soon as the pilot ignition circuit is energized (listen for
the sound of the solenoid valve opening or watch the pilot
gas pressure gauge), let about 3 to 4 seconds lapse and
then CAREFULLY (the ignition transformer is putting out
6000 volts) touch the ignition leadwire to the transformer
terminal secondary.
If the pilot fuel/air mixture and ignition electrode are
adjusted correctly, the pilot will light instantly and the
flame signal reading will be steady and of the correct
value. If the pilot does not light instantly, then readjust
the pilot gas pressure and/or the air dampers and/or the
ignition electrode setting according to the information
provided in this manual.
6.
Turn the burner off. Reconnect the ignition leadwire to
the ignition transformer secondary terminal. Set the
“check” switch in the flame safeguard control for
automatic operation. Reconnect any wires that have
been disconnected to hold the motorized gas valve in the
pilot position. Open the checking gas cock, turn the
burner on and verify that the pilot lights and proves
instantly, providing good, smooth ignition of the main gas
flame.
7.
If Gas Pilot Flood Test is successful, it is not always a
guarantee of correct pilot air/fuel mixture, but a failure will
almost always indicate an excessively rich mixture.
(page 3-987)
