Meter Flow Rate; Gas Rate Cubic Feet Per Hour - Lennox G21Q3-40 Unit Information

Secs
Size of Test Dial
for
One 1 2
Rev. cu. ft. cu. ft. cu. ft.
10 360 720 1800
11 327 655 1636
12 300 600 1500
13 277 555 1385
14 257 514 1286
15 240 480 1200
16 225 450 1125
17 212 424 1059
18 200 400 1000
19 189 379
20 180 360
21 171 343
22 164 327
23 157 313
24 150 300
25 144 288
26 138 277
27 133 267
28 129 257
29 124 248
30 120 240
31 116 232
32 113 225
33 109 218
EXAMPLE:
a − One revolution of two foot dial = 90 seconds.
b − Using the gas rate chart, table 16, note that 90 sec
onds = 80 cubic feet of gas per hour.
c − 80 cu. ft./hr. x 1000 Btuh/cu. ft. = 80,000 Btuh in
put.
d − Normally there are 1000 Btuh in each cubic foot of
gas. Make adjustment to this figure where the gas
heating value is other than 1000 Btuh per cubic
foot (contact the local gas supplier for local Btuh
per cubic foot ratings).
N − Checking Air Intake and Flapper Valve
Figures 70, 71 and 72
1 − Remove air intake chamber cover and check foreign
materials that may have accumulated, clean purge
blower and upper and lower chamber compartment if
necessary.
2 − Do not remove air flapper valve unless it is suspected
of being faulty.
If valve must be removed, carefully remove the eight
screws holding air intake flapper valve to valve body. DO
NO TURN OR REMOVE CENTER SCREW. Remove
valve from unit. CAUTION DO NOT DROP.
3 − EXTREME CARE SHOULD BE TAKEN WHEN DISAS
SEMBLING INTERNAL COMPONENTS OF THE
VALVE. If taken apart, plates could be rotated out of
phase or reversed. Spacer thickness has an extremely
low tolerance. Note that each plate has a stamp of the
spacer thickness and a star or the words THIS SIDE
OUT." These stamps should all lie in the same quadrant
and face the outside of unit. See figures 71 and 72. New
er air flapper valve assemblies for the −40 / 50 / 60 / 80
contains a plate made from PPS thermoplastic with a

GAS RATE CUBIC FEET PER HOUR

Secs
Size of Test Dial
for
5 One 1 2
Rev. cu. ft. cu. ft.
34 106 212
35 103 206
36 100 200
37 97 195
38 95 189
39 92 185
40 90 180
41 − 176
42 86 172
947 43 − 167
900 44 82 164
857 45 80 160
818 46 78 157
783 47 − 153
750 48 75 150
720 49 − 147
692 50 72 144
667 − − −
643 52 69 138
621 54 67 133
600 56 64 129
581 58 62 124
563 60 60 120
545 − − −
TABLE 16

METER FLOW RATE

Secs
Size of Test Dial
for
One
5 2
Rev.
cu. ft. cu. ft.
529 62 116
514 64 112
500 66 109
486 68 106
479 70 103
462 72 100
450 74 97
439 76 95
429 78 92
419 80 90
409 82 88
400 84 86
391 86 84
383 88 82
375 90 80
367 92 78
360 94 −
− 96 75
346 98 −
333
100 72
321
102 −
310
104 69
300
106 −
−
108 67
grooved surface on one side. The grooved surface should
be facing towards the flapper. Earlier −40/50/60/80 models
will have a stainless steel back plate with a star stamped
on the surface. This star must face away from the flapper
when assembled. On all −40/50/60/80 models, the front
plate will have a stamp and star on the surface and must
face away from flapper.
4 − Visually inspect flapper. On new units, the flapper may
not be perfectly flat, it may be curved or dished between
the plates. This is normal. On units that have had suffi
cient run in time, the flapper will be flat. If the flapper is torn,
creased or has uneven (frayed) edges, the material must
be replaced. A flapper material is available from Lennox
Repair Parts. Flapper should be replaced every four
years.
5 − To find potential warpage in the plates, check for the re
quired clearance between the flapper and back plate in
several places around the circumference of the valve.
See figure 73. Use a feeler gauge, starting small and
working up to the clearance dimension until the gauge
is just about snug.
Do not force feeler gauge between flapper and
back plate. Damage to flapper material will occur.
Clearance should be checked in six or eight places
around the valve. If valve is out of clearance at any
one point, replace the assembly. Required clear
ance values are listed in table 17. Clearances are
updated regularly in Service and Application Notes.
Page 51
Secs
Size of Test Dial
for
5 One 2
cu. ft. Rev. cu. ft.
290 110 −
281 112 64
273 116 62
265 120 60
257 125 −
250 130 −
243 135 −
237 140 −
231 145 −
225 150 −
220 155 −
214 160 −
209 165 −
205 170 −
200 175 −
196 180 −
192 − −
188
51 141
184 53 136
55 131
180
57 126
176
59 122
173
− −
170
− −
167
WARNING
5
cu. ft.
164
161
155
150
144
138
132
129
124
120
116
113
109
106
103
100
−
353
340
327
316
305
−
−