(6.) Follow heat value and specific gravity lines to point of intersection. Find orifice size and manifold pressure settings for proper
operation at given natural gas conditions.
EXAMPLE:
Heat value 1070 Btu/cu ft
Specific gravity 0.58
Therefore; Orifice No. 44 *
Manifold pressure 3.6-in. wc
* The furnace is shipped with No. 43 orifices. Therefore, in this example all main burner orifices must be changed and the manifold pressure
must be adjusted.
(7.) Proceed to item c. to adjust manifold pressure.
b. Check gas input rate by clocking gas meter.
Table 7—Model GB3AAV Orifice Size and Manifold Pressure for Correct Input Rate*
(Tabulated Data Based on Altitude Up to 2000 ft and 23,000 Btuh Per Burner)
GAS HEAT VALUE
(BTU/CU FT)
SPECIFIC GRAVITY OF NATURAL GAS
0.56
0.58
0.60
0.62
0.64
0.66
0.68
0.70
0.72
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
Orf
No.
Mnfld
Press.
860
40
41
—
3.2
3.5
—
40
41
39
3.3
3.6
—
40
41
39
3.4
3.7
3.2
40
41
39
3.5
3.8
3.3
40
38
39
3.7
3.2
3.4
40
38
39
3.8
3.3
3.5
—
38
39
—
3.4
3.6
37
38
39
3.2
3.5
3.8
37
38
—
3.2
3.6
—
875
—
41
42
—
3.3
3.7
40
41
—
3.2
3.5
—
40
41
—
3.3
3.6
—
40
41
39
3.4
3.7
3.2
40
41
39
3.5
3.8
3.3
40
38
39
3.6
3.2
3.4
40
38
39
3.8
3.3
3.5
—
38
39
—
3.4
3.6
—
38
39
—
3.4
3.7
890
—
41
42
—
3.2
3.6
—
41
42
—
3.4
3.7
40
41
—
3.2
3.5
—
40
41
—
3.3
3.6
—
40
41
39
3.4
3.7
3.2
40
41
39
3.5
3.8
3.3
40
—
39
3.6
—
3.4
40
38
39
3.7
3.2
3.5
40
38
39
3.8
3.3
3.6
905
—
—
42
—
—
3.5
—
41
42
—
3.2
3.6
—
41
42
—
3.4
3.7
40
41
—
3.2
3.5
—
40
41
—
3.3
3.6
—
40
41
39
3.4
3.7
3.2
40
41
39
3.5
3.8
3.3
40
—
39
3.6
—
3.4
40
38
39
3.7
3.2
3.5
920
—
—
42
—
—
3.4
—
—
42
—
—
3.5
—
41
42
—
3.2
3.6
—
41
42
—
3.4
3.7
40
41
42
3.2
3.5
3.8
40
41
—
3.3
3.6
—
40
41
39
3.4
3.7
3.2
40
41
39
3.5
3.8
3.3
40
—
39
3.6
—
3.4
935
42
—
—
3.3
—
—
42
—
—
3.4
—
—
42
—
—
3.5
—
—
42
—
41
3.6
—
3.2
42
—
41
3.7
—
3.4
42
40
41
3.8
3.2
3.5
—
40
41
—
3.3
3.6
39
40
41
3.2
3.4
3.7
39
40
41
3.3
3.5
3.8
950
42
—
—
3.2
—
—
42
—
—
3.3
—
—
42
—
—
3.4
—
—
42
—
—
3.5
—
—
42
—
41
3.6
—
3.2
42
—
41
3.7
—
3.3
42
40
41
3.8
3.2
3.5
—
40
41
—
3.3
3.6
39
40
41
3.2
3.4
3.7
965
—
43
—
—
3.7
—
42
—
—
3.2
—
—
42
—
—
3.3
—
—
42
—
—
3.4
—
—
42
—
—
3.5
—
—
42
—
41
3.6
—
3.2
42
—
41
3.7
—
3.3
42
40
41
3.8
3.2
3.4
—
40
41
—
3.3
3.5
980
—
43
—
—
3.6
—
—
43
—
—
3.7
—
42
—
—
3.2
—
—
42
—
—
3.3
—
—
42
—
—
3.4
—
—
42
—
—
3.5
—
—
42
—
41
3.6
—
3.2
42
—
41
3.7
—
3.3
42
44
41
3.8
3.2
3.4
995
—
43
—
—
3.5
—
—
43
—
—
3.6
—
—
43
—
—
3.8
—
42
—
—
3.2
—
—
42
—
—
3.3
—
—
42
—
—
3.4
—
—
42
—
—
3.5
—
—
42
—
41
3.6
—
3.2
42
—
41
3.7
—
3.3
1010
—
43
—
—
3.4
—
—
43
—
—
3.5
—
—
43
—
—
3.6
—
—
43
—
—
3.6
—
42
—
—
3.2
—
—
42
—
—
3.3
—
—
42
—
—
3.4
—
—
42
—
—
3.5
—
—
42
—
41
3.6
—
3.2
1025
—
43
44
—
3.3
3.8
—
43
—
—
3.4
—
—
43
—
—
3.5
—
—
43
—
—
3.7
—
—
43
—
—
3.8
—
42
—
—
3.2
—
—
42
—
—
3.3
—
—
42
—
—
3.4
—
—
42
—
—
3.5
—
—
1035
—
43
44
—
3.2
3.7
—
43
44
—
3.3
3.8
—
43
—
—
3.4
—
—
43
—
—
3.6
—
—
43
—
—
3.7
—
—
43
—
—
3.8
—
42
—
—
3.2
—
—
42
—
—
3.3
—
—
42
—
—
3.4
—
—
1055
—
—
44
—
—
3.6
—
43
44
—
3.2
3.7
—
43
44
—
3.3
3.8
—
43
—
—
3.5
—
—
43
—
—
3.6
—
—
43
—
—
3.7
—
—
43
—
—
3.8
—
42
—
—
3.2
—
—
42
—
—
3.3
—
—
1070
—
—
44
—
—
3.5
—
—
44
—
—
3.6
—
43
44
—
3.3
3.7
—
43
44
—
3.4
3.8
—
43
—
—
3.5
—
—
43
—
—
3.6
—
—
43
—
—
3.7
—
—
43
—
—
3.8
—
42
—
—
3.2
—
—
1085
—
44
—
3.4
—
44
—
3.5
43
44
3.2
3.6
43
44
3.3
3.7
43
—
3.4
—
43
—
3.5
—
43
—
3.6
—
43
—
3.7
—
43
—
3.8
—
1100
—
44
—
3.3
—
44
—
3.4
—
44
—
3.5
43
44
3.2
3.6
43
44
3.3
3.7
43
—
3.4
—
43
—
3.5
—
43
—
3.6
—
43
—
3.7
—
*For size 060135 only, deduct 0.1-in. wc from manifold pressure shown in table due to 22,500 Btuh per burner input. If resultant manifold pressure falls below 3.2-in. wc,
change orifice size.
—16—
