PART I: SPECIFICATIONS
13
Combustion head gas pressure curves
Combustion head gas pressure depends on gas flow and combustion chamber backpressure. When backpressure is subtracted, it
depends only on gas flow, provided combustion is properly adjusted, flue gases residual O2 percentage complies with “Recommended
combustion values” table and CO in the standard limits). During this stage, the combustion head, the gas butterfly valve and the
actuator are at the maximum opening. Refer to , showing the correct way to measure the gas pressure, considering the values of
pressure in combustion chamber, surveyed by means of the pressure gauge or taken from the boiler’s Technical specifications.
.
Measuring gas pressure in the combustion head
In order to measure the pressure in the combustion head, insert the pressure gauge probes: one into the combustion chamber’s pres-
sure outlet to get the pressure in the combustion chamber and the other one into the butterfly valve’s pressure outlet of the burner. On
the basis of the measured differential pressure, it is possible to get the maximum flow rate: in the pressure - rate curves (showed on the
next paragraph), it is easy to find out the burner’s output in Stm
3
/h (quoted on the x axis) from the pressure measured in the combu-
stion head (quoted on the y axis). The data obtained must be considered when adjusting the gas flow rate.
Pressure - rate in combustion head curves (natural gas)
WARNING: the diagrams refers to natural gas. For different type of fuel please refer to the paragraph “Fuel” at
the beginning of this chapter.
The values in the diagrams refer to
natural gas
with a calorific value of 8125 kcal/Stm
3
(15°C, 1013 mbar) and a density of
0.714 kg/Stm
3
.
The values in the diagrams refer to
GPL
with a calorific value of 22300 kcal/Stm
3
(15°C, 1013 mbar) and a density of 2.14 kg/
Stm
3
. When the calorific value and the density change, the pressure values should be adjusted accordingly.
Curves are referred to pressure = 0 mbar in the combustion chamber!
Where:
Natural gas pressure shown in diagram
Real gas pressure
Natural gas flow rate shown in diagram
Real gas flow rate
Natural gas density shown in diagram
Real gas density
1
2
4
3
Note: the figure is indicative only.Key
1 Generator
2 Pressure outlet on the combustion chamber
3 Gas pressure outlet on the butterfly valve
4 Differential pressure gauge
Fig. 1
ATTENTION: THE BURNED GAS RATE MUST BE
READ AT THE GAS FLOW METER. WHEN IT IS NOT
POSSIBLE, THE USER CAN REFERS TO THE
PRESSURE-RATE CURVES AS GENERAL
INFORMATION ONLY.
