Specifications

IM 685-2 13
Service
General
Before starting service on this burner take the time to read
the sections “About This Burner” on page 8 and “Typical
Sequence of Operation” on page 11 to get an overview.
Gun Assembly
The McQuay gas burner gun assembly is easily removable
and includes the ignition electrode assembly, the flame rod
assembly, and a “Base Air” fitting with orifice. The position-
ing of this assembly is not considered field adjustable. When
positioned correctly the gun disc will be perpendicular to the
blast tube and back in the cylindrical portion of the blast tube
as shown in Figure 8. The gun pipe will be concentric with
the blast tube.
Figure 8. Gun Assembly
Gun Assembly Removal and Installation
Unplug the ignition lead from the ignition electrode and
unplug the flame rod lead from the flame rod. Disconnect the
3/8 inch copper tube at the brass fitting on the left side of the
gun pipe, open the pipe union and remove the gun assembly.
Models 050-200 include an air tube that must be lifted up
and out of the grommeted hole it is nested into as the gun
assembly is removed. The gun assembly may have to be
manipulated and wiggled as the disc is withdrawn back
through the blast tube. Reassemble in reverse order, being
particularly careful to correctly reinsert the air tube into the
grommeted hole. The tube should slip into the grommet so
there is little leakage, but it should not bear down on it or it
can cause binding on the sliding air valve. Always remove
shoulder screw (12), Figure 16a, and manually slide the con-
trol rod back and forth to test for binding after reinstalling
the gun assembly on Models HT050-200. Do not operate the
burner without a tight seal at the grommet.
Flame Rod Adjustment
The gun assembly is removed for flame rod inspection or
service. When correctly adjusted the flame rod insulator will
be concentric with the hole it passes through, not be shorted
out against the disc, the 0.75 inch long end tip will point
toward the 0.086 inch diameter alignment hole, and the end
tip will clear the disc according to dimension “C” in Figure
9.
Figure 9. Flame Rod and Ignition Electrode
Flame Rod Installation
The flame rod must be disassembled from its porcelain insu-
lator for removal or installation. Remove the two nuts on the
threaded end of the flame rod, pull the rod out of the insula-
tor, and then remove the insulator by loosening its clamp
screw.
Ignition Electrode Adjustment
The gun assembly is removed for ignition electrode inspection
or service. When correctly adjusted the ignition electrode
insulator will he concentric with the hole it passes through, the
end of the insulator will be flush with the outside surface of
the gun disc, the electrode tip will point toward the 0.086 inch
diameter alignment hole, and there will be a 0.09 inch spark
gap to the gun disc (see Figure 9). The ignition electrode can
he removed by loosening the clamp screw and sliding the
entire assembly through the disc hole.
Model HT*** A B
Base Air
Orifice I.D.
020 1.98 1.94 .060
025 2.04 1.88 .060
032 2.04 1.88 .067
040 2.17 1.75 .070
050 2.17 1.75 .089
064 217 1.75 .089
065 2.17 1.75 .089
079 2.07 1.85 .102
080 2.07 1.85 .102
100 2.30 1.62 .102
110 2.24 1.68 .098
140 2.30 1 62 .110
150 4.13 1.62 .110
200 4.13 1.62 .110
Model HT*** C
020 .09
025 .09
032 .09
040 .09
050 .40
064 .40
065 .40
079 .40
080 .40
100 .44
110 .35
140 .35
150 .48
200 .75
BASIC AIR
ORIFICE
A
B
ALIGN FLAME ROD TIP
WITH .086 DIA HOLE
IN BURNER DISC.
.086 DIA.
HOLE (REF.)
ALIGN IGNITION
ELECTRODE TIP
WITH .086 DIA HOLE
IN BURNER DISC.
.086 DIA. HOLE
(REF.)
.09
C
FLAME ROD
IGNITION
ELECTRODE