CPD Review Manual
NOTES
Equation 14-1
Q0.381
1,917 (∆H/[Cr x L])0.206
where
D = Inside diameter of the pipe, in.
Q = Input rate appliance, cfh at 60°F
L = Equivalent length of pipe, ft
∆H = Pressure drop (upstream pressure – downstream pressure), in. wc
Cr = Natural gas: 0.6094; Undiluted propane:1.2462
D=
Equation 14-2
Q0.381
18.93 [(P1 – P22)*Y/(Cr x L)]0.206
where
P1 = Upstream pressure, pounds per square inch absolute (psia) (P1+14.696)
P2 = Downstream pressure, psia (P1+14.696)
Y = Natural gas: 0.9992; Undiluted propane: 0.9910
D=
2
Longest Length Method
This is the traditional method used to determine the longest equivalent piping length (from
the meter or delivery point to the farthest outlet), which then is used in conjunction with
pipe sizing tables to determine the appropriate pipe diameter for all other sections of piping
in the system. In simple terms, only the cfh quantities listed in the tables for this pipe length
are used to size each branch and section of pipe. This method is the simplest to use, and
it generally yields the
most conservative siz- Table 14-1 Capacity of Gas Pipe for Pressures Less than 2
psi (where SG = 0.6 and pressure drop = 0.3 in. wc), cfh
ing because the short
Pipe size, in. nominal
runs of piping located Pipe
Length,
close to the meter can
½ ¾
1
1¼
1½
2
2½
3
4
ft
be somewhat over10
131 273 514 1,060 1,580 3,050 4,860 8,580 17,500
sized. One advantage
20
90 188 353 726 1,090 2,090 3,340 5,900 12,000
of using this method
30
72
151 284 583
873 1,680 2,680 4,740 9,660
is that it can provide
40
62 129 243 499
747 1,440 2,290 4,050 8,270
some cushion in the
50
55
114
215
442
662 1,280 2,030 3,590 7,330
branch piping, al60
50 104 195 400
600 1,160 1,840 3,260 6,640
lowing for future re70
46 95 179 368
552 1,060 1,690 3,000 6,110
configuration of the
piping system with80
42 89 167 343
514
989 1,580 2,790 5,680
out replacing entire
90
40 83 157 322
482
928 1,480 2,610 5,330
branch lengths.
100
38 79 148 304
455
877 1,400 2,470 5,040
Table 14-1 can 125 33 70 131 269
403
777 1,240 2,190 4,460
be used to determine 150 30 63 119 244
366
704 1,120 1,980 4,050
the capacity of a wide 175 28 58 109 224
336
648 1,030 1,820 3,720
range of pipe sizes to 200 26 54 102 209
313
602
960 1,700 3,460
be used in the longest
250
23 48 90
185
277
534
851 1,500 3,070
length method. Table
300
21 43 82
168
251
484
771 1,360 2,780
14-1 is a tabular solu350
19 40 75
154
231
445
709 1,250 2,560
tion of the Spitzglass
215
414
660 1,170 2,380
formula for the case 400 18 37 70 143
450
17
35
66
135
202
389
619 1,090 2,230
where the specific
191
367
585 1,030 2,110
gravity S = 0.6 and the 500 16 33 62 127
550
15
31
59
121
181
349
556
982
2,000
pressure drop H = 0.3
173
333
530
937
1,910
in. wc. If the gas used 600 14 30 56 115
165
318
508
897
1,830
for the system has a 650 14 29 54 110
108
Section 2: Design — Chapter 14: Fuel Gas Systems
Table 14-2 Specific
Gravity Capacity
Multipliers
Specific
Multiplier
Gravity
0.35
1.310
0.40
1.230
0.45
1.160
0.50
1.100
0.55
1.040
0.60
1.000
0.65
0.962
0.70
0.926
0.75
0.895
0.80
0.867
0.85
0.841
0.90
0.817
1.00
0.775
1.10
0.740
1.20
0.707
1.30
0.680
1.40
0.655
1.50
0.633
1.60
0.612
1.70
0.594
1.80
0.577
1.90
0.565
2.00
0.547
2.10
0.535
Table 14-3
Conversion Factors
for Pressure Drop
Pressure
Multiplier
Drop
1.00
2.236
0.90
2.121
0.80
2.000
0.70
1.871
0.60
1.732
0.50
1.561
0.40
1.414
0.35
1.323
0.30
1.225
0.25
1.118
0.20
1.000
0.10
0.707
Table 14-4 Conversion Factors
for Pipe Lengths
X*
Multiplier X*
Multiplier
1.0
1.000
3
0.577
1.1
0.953
4
0.500
1.2
0.913
5
0.447
1.3
0.877
6
0.408
1.4
0.845
7
0.378
1.5
0.817
8
0.354
1.6
0.791
9
0.333
1.7
0.767
10
0.316
1.8
0.745
20
0.224
1.9
0.725
30
0.182
2
0.707
NOTES
*X = Length of pipe divided by length given in Table
14-1 for Q
different specific gravity, obtain the multiplier from Table 14-2.
Table 14-3 shows the conversion factors for pressure drop, and
Table 14-4 shows the conversion factors for pipe length.
In all cases, the pressure drop is for the length given and not
the drop per 100 feet. A value of 0.2 is recommended for horizontal piping and 0.5 for vertical piping.
The purpose of Table 14-4 is to find the conversion factor to
use for values of L other than those in Table 14-1. The multiplier
is to be applied to the value of Q in Table 14-1. For example, Table
14-1 does not give Q for an L of 1,000 feet. In this case, use the
value of Q for 500 feet; thus, X is then 1,000/500 = 2, and the value of Q from Table 14-1 for 500 feet is multiplied by 0.707 (from
Table 14-4).
Example 14-1
What would be the capacity of a 110-foot run of 1¼-inch gas piping with a 0.45 specific
gravity gas and a pressure drop of 0.35 inch?
From Table 14-1, the capacity of 100 feet of 1¼-inch pipe is 230 cfh at a 0.65 specific
gravity and 0.2-inch pressure drop. From Table 14-2, for a 0.45 specific gravity, the multiplier is 1.202. From Table 14-3, for a 0.35 pressure drop, the multiplier is 1.323. To correct for
the length, X = 110/100 = 1.1, and the multiplier for 1.1 in Table 14-4 is 0.953. Therefore,
the correct capacity is 230 × 1.202 × 1.323 × 0.953 = 348.6 cfh.
Branch Length Method
This is an alternate sizing method that could allow slightly smaller pipe diameters in some
segments of a piping system when compared to the longest length method. The pipe size of
each section of the longest pipe length (from the meter or delivery point to the farthest outlet) shall be determined using the longest equivalent length of piping and the associated cfh
quantity listed in the tables for that section. Then, the pipe sizes of each section of branch
piping not previously sized shall be determined using the equivalent lengths of piping from
the point of delivery to the most remote outlet of each individual branch and the associated
cfh quantity listed for that particular section.
Hybrid Pressure Method
This method is used when it is necessary to design a piping system that utilizes multiple supply pressures within a single distribution system. The pipe size for each section of
high-pressure gas piping shall be determined using the longest equivalent length of piping
from the meter or delivery point to the farthest pressure regulator. The pipe size from the
109