750-392
CBEX-DE
3-9
Gas Pressure and Flow Information
3.8.1 — 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 3-2 for pressure
requirements. For gas fuels other than natural gas please contact the factory.
Regulated Pressure is the pressure required downstream of the main gas train regulator. Manifold pressure is the
pressure required downstream of the gas butterfly valve at high fire. There is typically a tapping on the elbow for
measuring manifold pressure.
The pressures listed are based on 1000 Btu/cu ft natural gas at elevations up to 700 feet above sea level. For
installation at higher altitudes, multiply the selected pressure by the proper factor from Table 3-3.
TABLE 3-2. Minimum gas pressure required
30 ppm 60 ppm
BOILER
HP
REGULATED PRESSURE
inches WC
MANIFOLD PRESSURE
inches WC
REGULATED PRESSURE
inches WC
MANIFOLD PRESSURE
inches WC
250 35.0 23.0
300 35.0 22.6
350 45.1 23.6
400 44.2 27.2
500 44.0 27.7
600 55.2 31.8
700 58.0 33.4 57.2 34.9
800 74.2 46.4 71.2 43.8
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