A.O. Smith HW 610 warranty Example, Specific Multiplier Gravity, GAS Pressure Regulators

•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	Multiplier	Specific	Multiplier
Gravity		Gravity
.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)

GAS VALVE KNOB

PRESSURE REGULATOR

ADJUSTMENT

INLET

PILOT

OUTLET

PILOT ADJUSTMENT

GAS (UNDER CAP SCREW)

CONTROL

PILOT ADJUSTMENT	OUTLET
UNDER SCREW	PILOT SUPPLY

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	Rated	Manifold Pressure
Number	Input	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

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