Purging - A.O. Smith DB/DW-720-1810 User Manual

PURGING

Gas line purging is required with new piping or systems in which
air has entered.
PURGING SHOULD BE PERFORMED BY PERSONS
EXPERIENCED IN THIS TYPE OF GAS SERVICE TO AVOID RISK
OF FIRE OR EXPLOSION. PURGE DISCHARGE MUST NOT
ENTER CONFINED AREAS OR SPACES WHERE IGNITION CAN
OCCUR. THE AREA MUST BE WELL VENTILATED AND ALL
SOURCES OF IGNITION MUST BE INACTIVATED OR REMOVED.
BEFORE PLACING THE BOILER IN OPERATION, CHECK FOR
GAS LEAKAGE. Use soap and water solution or other material
acceptable for the purpose in locating gas leaks. DO NOT USE
MATCHES, CANDLES, FLAME OR OTHER SOURCES OF
IGNITION FOR THIS PURPOSE.
1. CORRECT GAS
Make sure the gas on which the boiler will operate is the same as
that specified on the boiler rating plate. Do not install the boiler if
equipped for a different type gas, consult your gas supplier. These
boilers are designed to operate on natural gas only.
MAXIMUM CAPACITY OF PIPE IN CUBIC FEET OF GAS PER HOUR (BASED UPON A PRESSURE DROP OF
Length in Feet (Meters)
From Gas Meter
10 (3)
20 (6)
30 (9)
40 (12)
50 (15)
60 (18)
70 (21)
80 (24)
90 (27)
100 (30)
125 (38)
150 (46)
175 (53)
200 (61)
*The heating value of natural gas is approximately 1050 Btu/ft³.
Propane (L.P.) gas has a heating value of approximately 2500 Btu/ft³.
CAUTION
0.3 INCH WATER COLUMN AND 0.6 SPECIFIC GRAVITY GAS)
1/2 3/4 1
132 278 520
92 190 350
73 152 285
63 130 245
56 115 215
50 105 195
46 96 180
43 90 170
40 84 160
38 79 150
34 72 130
31 64 120
28 59 110
26 55 100
Multipliers To Be Used With Table 1 When Applying The
Gravity Factor To Other Than .60 Specific Gravity
Specific
Gravity Multiplier
.35 1.31
.40 1.23
.45 1.16
.50 1.10
.55 1.04
*.60 (Nat.) 1.00
.65 .96
.70 .93
.75 .90
.80 .87
.85 .84
.90 .82
*Use these correction factors if exact specific gravity of the gas is not known.
2A. SIZING GAS SUPPLY LINE (For single boiler installations
and for installations of multiples of two or three of same size
boilers).
Use table 1, which is taken from ANSI booklet Z223.1, NATIONAL
FUEL GAS CODE, and/or CAN/CSA-B149.1-00 to size iron pipe
or equivalent gas supply line. Table 4 is based on a pressure drop
of 0.3 inches of water and a specific gravity of 0.60 which is
approximately for natural gas. (LP gas has an S.G. of about 1.53).
If the service pressure is five inches water column or less, use one
pipe size larger than specified in table 1 in order to minimize pressure
drop in the line.
2B. SIZING GAS SUPPLY LINE (For multiples of over three boilers
of same size or for multiple installations of two or more mixed
sizes).
Capacities in cubic feet per hour of 0.60 specific gravity gas for
different sizes and lengths are shown in table 4. No additional
allowance is necessary for an ordinary number of fittings.
Where it is necessary to use more than the average number of
pipe fittings i.e. elbows, tees, and valves in gas supply line, use a
pipe larger than specified to compensate for increased pressure
drop.
TABLE 4
Nominal Iron Pipe Size, Inches (NPT)
1 1/4 1 1/2 2
1,050 1,600 3,050
730 1,100 2,100
590 890 1,650
500 760 1,450
440 670 1,270
400 610 1,150
370 560 1,050
350 530 990
320 490 930
305 460 870
275 410 780
250 380 710
225 350 650
210 320 610
TABLE 5
Specific
Gravity Multiplier
1.00 .78
1.10 .74
1.20 .71
1.30 .68
1.40 .66
*1.50 (Prop.) .63
1.60 .61
1.70 .59
1.80 .58
1.90 .56
*2.00 (Butane) .55
2.10 .54
10
2 1/2 3 4
4,800 8,500 17,500
3,300 5,900 12,000
2,700 4,700 9,700
2,300 4,100 8,300
2,000 3,600 7,400
1,850 3,250 6,800
1,700 3,000 6,200
1,600 2,800 5,800
1,500 2,600 5,400
1,400 2,500 5,100
1,250 2,200 4,500
1,130 2,000 4,100
1,050 1,850 3,800
980 1,700 3,500