Chapter 6 — Adjustment Procedures
6-16 Part No. 750-184
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 15.5" WC gas pressure at sea level (Table 6-1). Table
6-2 indicates a correction factor of 1.07 for 2,000 feet. Multiplying
the results in a calculated net regulated gas requirement of
approximately 16.6" WC. 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 and “correct” this answer by applying the
correction factor for 3 psig (Table 6-4).
Btu/hr Input = CFH (Cubic feet/hour)
Btu/cu-ft
OR
8,369,000
= 8,369 CFH (At 14.7 Ib-atmospheric base 1,000 pressure)
THEN
8,369
= 7,092 CFH
1.18
This is the CFH (at line pressure) that must pass through the meter
so that the equivalent full input requirement of 25,100 CFH (at
base pressure) will be delivered.
Checking Gas Flow
Your gas supplier can generally furnish a gas meter flow chart from
which gas flow can be determined. After a short observation period,
the information aids in adjusting the regulator to increase or
decrease flow as required to obtain rated output.
Final adjustment of the gas fuel is carried out by means of the
adjusting screws in the gas modulating cam, while performing a
combustion efficiency analysis. See Section Q for details.
Note: The information given in this section is for all practical
purposes sufficient to set and adjust controls for gas
input. Your gas supplier can, if necessary, furnish exact
correction factors that take into consideration Btu
content, exact base pressure, specific gravity,
temperature, etc., of the gas used.
Q. GAS FUEL COMBUSTION ADJUSTMENT
After operating for a sufficient period of time to assure a warm
boiler, adjustments should be made to obtain efficient combustion.
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