Service
General
) has
a pre-mix pilot burner . The pilot pressure gauge tap (2) is a
capped 1/4
"
flare male connection which can be connected
to a manometer to measure both pilot air and gas pressures .
Thus, these adjustments can be accurately made and checked
with instruments . This manometer connection is also useful in
troubleshooting the pilot . Failure of the pilot pressure regulator,
pilot gas valves, and plugged or improper gas or air openings
are easily diagnosed with the manometer .
Pilot Air & Gas Adjustments
A manometer connected to the pilot pressure gauge tap (2)
(see
) will indicate pilot air pressure
when the pilot gas valve is closed, as during the prepurge
period, and will indicate gas pressure on the pilot orifice when
the pilot gas valve is open . Thus both readings are taken from
this one test connection .
1 . Connect manometer to pilot tap (2) .
2 . While the burner fan is running, the pilot gas valve is
closed, and the modulating burner has its air damper at
the low fire position; read the pilot air pressure. Typical
readings are shown in column 5 on
.
3 . At the completion of the prepurge period, the pilot valve
will open and the manometer will then read pilot gas
pressure . Typical readings are shown in column 7 on
4 .
Pilot flame signal readings should be 2.5 to 4.0 volts DC
and steady at the low fire position when only the pilot is
operating. When the main burner flame is also burning
the readings will be higher .
5 .
A single stage burner that does not have low fire start,
and always operates at “high fire” should have pilot flame
signal readings of 2 .0 to 3 .2 volts DC and steady when
only the pilot is operating. When the main burner flame is
also burning the readings will change .
6 . The pilot gas and pilot air pressure readings shown in
Table 7
are typical . The pilot gas and pilot air pressure
should be adjusted for optimum flame signal, not
necessarily with the values shown in
7 .
Vary the pilot gas pressure regulator and find the
midpoint of the peak gas pressure that produces the
highest pilot flame signal voltage. The voltage should
decrease as the pressure is either decreased or
increased beyond that peak . If peak midpoint voltage
was obtained at gas pressures below 3 .0 inches W .C .,
this would indicate more pilot air is required and there is
a problem with the pilot air pickup tube . The pickup may
be out of adjustment, kinked, or damaged so it is not
providing adequate air to the pilot .
8 .
If the pilot flame signal voltage is within the range
specified above, use that peak midpoint setting as the
pilot gas pressure setpoint .
9 . Determine that the pilot will hold in satisfactorily at BOTH
high and low fire on modulating burners. Test this by
observing the flame signal as the burner repositions from
low fire to high fire.
10 .
The flame safeguard has a 10-second trial for ignition
period . A properly operating pilot will light and prove
itself to the flame safeguard within one second. If it takes
longer than one or two seconds to prove pilot flame, the
pilot is probably too lean and a higher pilot gas pressure
regulator adjustment is required .
Pressure Regulator
Approximate pilot gas pressure adjustments can be made
even when a manometer is not available . Snug the regulator
adjusting screw to the bottomed out position and back out
2-1/2 turns for 4 .0
"
W .C ., three turns for 3 .7
"
W .C ., 3-1/2 turns
for 3 .2
"
W .C ., or 4 turns for 2 .9
"
W .C .
Pilot Orifice
The pilot orifice (see
, Item 9) is threaded into the
pilot test tee (8) which must be removed to get access to the
pilot orifice, for orifice drill size, see
.
Ignition Electrode Adjustments
Adjust the ignition electrode (see
) . The purpose of
the porcelain bushing is to provide an air seal that prevents air
from blowing into the pilot burner through the ignition electrode
hole . Because the bushing provides an air seal, it must be in
close contact with the countersunk surface on the pilot burner,
and gently held in place by the spring . The bushing should be
perpendicular to the hole .
• The electrode tip should be centered within the 0 .25
inch hole and be flush with the inside surface of the pilot
burner or project up to 0 .03 inches into the burner . The
ignition spark occurs between the electrode tip and the
edge of that 0 .25 inch hole, to the point on that hole that
is closest to the electrode . If the electrode is not centered,
that closest point results in a shorter spark gap and
consequently less of a spark to ignite the pilot . The spring
will allow the bushing to be slid back from the hole to get
a better view to check the electrode tip centering .
•
Good alignment and fit may require slight repositioning of
the electrode within the clamp and/or bending the clamp
by gripping the electrode clamp with a pliers .
• Both ends of the bushing are the same . If the end that
mates with the pilot burner gets damaged or if there is an
imperfection in one end, the bushing can be reversed .
IM 684-6 • ROOFTOP SYSTEMS 16 www .DaikinApplied .com
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