A.O. Smith HW 610 - Manual (Page 22)

22
• In table 7 on page 21, select the row showing the distance to
the most remote outlet or the next longer distance if the table
does not give the exact length. This is the only distance used in
determining the size of any section of gas piping. If the gravity
factor is to be applied, the values in the selected row of table 7
are multiplied by the appropriate multiplier from table 8.
• Total the gas demands of all appliances on the piping system.
Enter table 7, on the left hand side, at the row equal to or just
exceeding the distance to the most remote outlet. Select the
pipe size in the row with a capacity equal to or just exceeding
the total gas demand. This is the required main gas supply line
size leading away from the gas meter or regulator. To determine
the pipe size required for each branch outlet leading away from
the main supply line, determine the gas demand for that outlet.
Enter table 7 on the same row, and select the branch pipe
size for a capacity equal to or just exceeding the demand at
that outlet. The main line can be resized for a lesser capacity
after each branch outlet, since the gas demand is reduced.
Total the gas demands of all remaining appliances branching
off downstream on the main gas line. Re-enter table 8 in the
same row and select the appropriate pipe size with adequate
capacity. Repeat the branch sizing and main line re-sizing for
any remaining appliances in the system.
EXAMPLE
Job Condition:
Determining the required gas pipe size for a system composed of two
HW-420 boilers and two HW-610 boilers to be installed as a multiple
group, 50 lineal feet from meter. Gas to be used has a .60 specific
gravity and heating value of 1,000 Btu per cubic foot.
Solution:
2 HW-420 Boilers = 840,000 Btuh
2 HW-610 Boilers = 1,220,000 Btuh
Total Btuh Input = 2,060,000 Btuh
Total Btuh Input = 2,060,000 Btuh = 2,060 cf/h
Btu per Cubic Foot of Gas 1,000
With a cubic foot per hour demand of 2,060 and with 50 lineal
feet of gas supply line, table 7 shows a pipe size of 3" (76mm)
is required.
NOTE: For other than .60 specific gravity, apply multiplier factor as
shown in table 8.
TABLE 8.
MULTIPLIERS TO BE USED WITH TABLE 7 WHEN APPLYING
THE GRAVITY FACTOR TO OTHER THAN .60 SPECIFIC GRAVITY
Specific
Gravity
Multiplier
Specific
Gravity
Multiplier
.35 1.31 1.00 .78
.40 1.23 1.10 .74
.45 1.16 1.20 .71
.50 1.10 1.30 .68
.55 1.04 1.40 .66
*.60 (Nat.) 1.00 *1.50 (Prop.) .63
.65 .96 1.60 .61
.70 .93 1.70 .59
.75 .90 1.80 .58
.80 .87 1.90 .56
.85 .84 *2.00 (Butane) .55
.90 .82 2.10 .54
*Use these correction factors if exact specific gravity of the gas is not known.
GAS PRESSURE REGULATORS
The gas pressure regulator is included in the combination gas valve,
Figure 15, and is set to operate on the gas specified on the boiler
model and rating plate.
GROUND
TERMINALS (2)
PILOT
OUTLET
GAS
CONTROL
PILOT ADJUSTMENT
(UNDER CAP SCREW)
PILOT SUPPLY
OUTLET
INLET
GAS VALVE KNOB
PRESSURE REGULATOR
ADJUSTMENT
PILOT ADJUSTMENT
UNDER SCREW
FIGURE 15.
Periodically check main burner, Figure 34 on page 39, and pilot
flame, Figure 35 on page 40, for proper operation. This should
be checked every six months.
Do not subject the gas valve to inlet gas pressures of more than 14"
W.C. (1/2 P.S.I.). If higher gas pressures are encountered, a service
regulator is necessary.
TABLE 9.
CORRECT MANIFOLD PRESSURE FOR FULL
BOILER INPUT (IN INCHES OF WATER COLUMN)
Model
Number
Rated
Input
Manifold Pressure
Natural Propane
HW-300 300,000 3.5 10.0
HW-399 399,000 3.2 9.5
HW-420 420,000 3.5 10.0
HW-520 520,000 3.5 10.0
HW-610 610,000 3.5 10.0
HW-670 Nat. 660,000 3.5
HW-670 Prop. 670,000 10.0