CleaverBrooks FLX 1000, Operation, Service And Parts Manual

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Adjustment Procedures Chapter 5
750-177 5-7
N. GAS PILOT FLAME ADJUSTMENT
The size of the gas pilot flame is regulated by adjusting the gas flow through the pilot gas regulator. The flame
must be sufficient to ignite the main flame and to be seen by the flame detector. But an extremely large flame
is not required. An overly rich flame can cause sooting or carbon buildup on the igniting electrode. Too small
a flame can cause ignition problems.
Although it is possible to visibly adjust the size of the pilot flame, it is preferable to obtain a microamp or
voltage reading of the flame signal.
The correct voltage or microamp readings can be found in the information supplied with the flame safeguard
system.
The program relay used may be of the type that provides message information that includes a constant flame
signal of dc voltage. In this case a separate dc voltmeter is not required.
O. GAS PRESSURE AND FLOW INFORMATION
Because of variables in both the properties of gas and the supply system, it will be necessary to regulate the
pressure of the gas to a level that produces a steady, dependable flame that yields highest combustion
efficiency at rated performance yet prevents overfiring. Once the optimum pressure has been established, it
should be recorded and periodic checks made to verify that the regulator is holding the pressure at this level.
Occasional modification in fuel composition or pressure by the supplier may, at times, require readjustment
to return the burner to peak efficiency.
Pressure
The gas supplied must provide not only the quantity of gas demanded by the unit, but must also be at a
pressure high enough to overcome the pressure-loss due to the frictional resistance imposed by the burner
system and the control valves.
The pressure required at the entrance to the burner gas train for rated boiler output is termed “inlet pressure.”
The gas pressure regulator must be adjusted to achieve the pressure to assure full input.
The inlet pressure requirement varies with boiler size, and types of gas train. Refer to Table 6-3 for pressure
require-ments.
The pressures listed are based on 1000 Btu/cu-ft natural gas at elevations up to 700 feet above sea level.
The volume of gas flow is measured in terms of cubic feet and is determined by a meter reading. The gas flow
rate required for maximum boiler output depends on the heating value (Btu/cu-ft) of the gas supplied (Table
5-1).
Pressure Correction
The flow rate outlined in Section P is based on a “base” pressure, which is usually atmospheric or 14.7 psia.
Meters generally measure gas in cubic feet at “line” or supply pressure. The pressure at which each cubic foot
is measured and the correction factor for the pressure must be known in order to convert the quantity indicated
by the meter into the quantity which would be measured at “base” pressure.
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 6-2
As An Example:
Assume that a 500Flextube boiler is rated for 5MMBtu/hr input is installed and equipped with a standard gas
train; and that 1,000 Btu natural gas is available with an incoming gas pressure of 3 psig. The flow
requirements can be determined as follows: