750-96 (revised 2010)
Model CB Packaged Boiler Manual
5-13
5.7 — Gas Pressure and Flow Information
To express the volume obtained from an actual meter reading into cubic feet at base pressure, it is necessary to
multiply the meter index reading by the proper pressure factor obtained from Table 4.
Conversely: To determine what the meter index reading should be in order to provide the volume of gas required
for input, divide the desired flow rate by the proper pressure correction factor. This answer indicates the number
of cubic feet at line pressure which must pass through the meter to deliver the equivalent number of cubic feet at
base pressure.
For example, assume:
• that a 100 horsepower boiler is installed at 2,000 feet above sea level
• is equipped with a standard gas train
• that 1,000 BTU natural gas is available with an incoming gas pressure of 3 psig
The pressure and flow can be determined as follows:
Pressure: Correction for the 2,000 feet altitude must be made since altitude has a bearing on the net regulated
gas pressure.The standard gas train requires 8.5” W.C. gas pressure at sea level. Table 2 indicates a correction
factor of 1.07 for 2,000 feet. Multiplying these results in a calculated net regulated gas requirement of approxi-
mately 9.1” W.C. This is the initial pressure to which the regulator should be adjusted. Slight additional adjustment
can be made later, if necessary, to obtain the gas input needed for burner rating.
Flow: Since the gas flow rate is based on standard conditions of flow, correction must be made for the supply
pressure through the meter of 3 psig. Determine the flow rate by dividing the BTU content of the gas into the
burner input (Table 3) and “correct this answer by applying the correction factor for 3 psig (Table 4).
BTU/hr Input
= CFH (Cubic Feet/Hour)
BTU/cu. ft.
OR
4,184,000
= 4,184 CFH
1,000 (at 14.7 lb. atmospheric “base” pressure)
TABLE 4. Pressure Correction Factors
Regulator Inlet
Pressure Pressure Factor
Regulator Inlet
Pressure Pressure Factor
1 psig 1.05 9 psig 1.59
2 psig 1.11 10 psig 1.66
3 psig 1.18 11 psig 1.72
4 psig 1.25 12 psig 1.81
5 psig 1.32 13 psig 1.86
6 psig 1.39 14 psig 1.93
7 psig 1.45 15 psig 2.00
8 psig 1.52
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