750-211 (revised 2009)
Promethean Boilers, Model 4WI Manual
6-13
6.16 — Gas Pressure and Flow Information
7. When a suitable flame as indicated in step 6 is obtained, replace the detector. Observe the reading on the micro-
ammeter. The reading should be between 2-1/4 and 5 micro amps when using a lead sulfide detector and a stan-
dard amplifier. See the flame signal table in the manufacturer’s bulletin for values of other combinations.
The flame signal indicated on the annunciator type relay should not be less than 10 Vdc, and may be as high as
20 Vdc or greater.
The reading must be steady. If the reading fluctuates, recheck the adjustment. Be sure that the flame detector is
properly seated and that the lens is clean.
8. Return the test switch to the “Run” position.
9. If main flame has not been previously established, proceed to do so in accordance with instructions elsewhere
in the manual.
10. The reading of the main flame signal should also be checked. Observe the flame signal for pilot alone, pilot and
main burner flame together and the main burner flame at high, low, and intermediate firing rate positions. Read-
ings should be steady and in the range indicated in step 7. If there are any deviations, refer to the troubleshoot-
ing section in the technical bulletin.
6.16 — 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 pres-
sure of the gas to a level that produces a steady, dependable flame that yields the highest combustion efficiency at
rated performance yet prevents over-firing. 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 effi-
ciency. Since the gas pressure regulator itself is usually furnished by others, detailed adjustment instructions and
adjusting procedures recommended by the manufacturer should be followed.
6.16.1 — 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, control
valves, and piping.
The pressure required at the entrance to the burner gas train for rated boiler output is termed “net regulated pres-
sure.” The gas pressure regulator must be adjusted to achieve the pressure to assure full input.
The pressure requirement varies with boiler size, altitude, and type of gas train. Refer to Table 6.1 for pressure
requirements.
TABLE 6-1. Minimum Net Regulated Gas Pressure for Rated Boiler Output
Boiler HP Std. Pipe Size (inches)
Pressure Required
(WC)
100 2 7.3
125 2-1/2 12
150 2-1/2 10.5
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