21
NATURAL GAS STARTING UP AND REGULATION
(for LPG operation see the relative chapter)
In order to proceed with starting up, it’s necessary, if the burner is three-phase, to check that the sense of rotation
of the motor is correct. If not already done so at the moment of connecting the burner to the gas pipeline, it’s
indispensable to carry a purge of the air contained in the pipeline. As a precaution, special care should be taken
and doors and windows should be opened. Open the pipe union on the pipeline situated near the burner and then
open a little the cut-off cock (or cocks).When the characteristic odour of gas can be smelled, close the cut-off
cock. Wait until the gas present in the room has dispersed, and then reconnect the burner to the gas pipeline.
Then proceed as follows:
1) Make sure that the discharge of combustion products can take place freely (chimney lock-gates should be
open) and that there is water in the boiler.
2) Open the combustion air regulator to the appropriate level (see “air shutter control servo regulation, type STA
5 B 0.36/8.3N23”) and open the air passage between the head and the flame disk (diffuser) to about a third
(see regulation of the combustion head BT 8769/2/GB - 0002932171).
3) Adjust the regulators on the safety and “first flame” valves so that the gas delivery (ignition flow rate) is at the
appropriate level.
N.B. Refer to the specific description of the operations necessary for setting the gas delivery rate according to
the type of valves fitted to the burner (see last page).
4) N.B. On some burner models, the thermostat of the 2 nd flame must be at 2 contacts (in exchange); plase do
refer to the eletric diagram of the specific burner, in case you haven’t the termostat in exchange at two contact,
plase do refer to the diagram 0002050151.
Switch off the second flame thermostat and send current to the burner by switching on the general switch. The
burner will thus be switched on and the pre-ventilation will be performed.
If the air pressure exceeds that value at which the air pressure switch has been set, the ignition transformer
will be connected and, subsequently, the gas valves (safety and operating) will be inserted. The valves open
completely is limited to the position at which the flow regulator incorporated in the operating valve has been
manually regulated. At first ignition, successive “shut downs” could occur, due to the following reasons:
a- The gas pipeline has not been adequately purged of air and therefore the quantity of gas is not sufficient to
allow for a stable flame.
b- A “shut down” with flame presence could be caused by flame instability in the ionisation zone, due to and
incorrect air/gas ratio. This can be remedied by varying the quantity of air and/or gas delivered, in order to find
the correct ratio. It could also be caused by an incorrect distribution of air/gas in the combustion head. This can
be corrected by operating the regulation device of the combustion head by closing or opening more the air
passage between the head and the gas diffuser. See chapter “regulation of the combustion head”.
c- It could happen that the ionisation current is help up by the current discharged from the ignition transformer
(the two currents have to run the same course on the burner’s ”earth”) and so the burner goes to “shut down”
due to insufficient ionisation. This can be remedied by inverting the input (230V side) of the ignition transformer
(change the places of the two wire that take voltage to the transformer). A shut down with flame presence
could also be caused by the burner’s casing not being properly “grounded”. We must point out that the minimum
value of the ionisation current to ensure the working of the control box is shown in the electrical diagram;
normally the ionisation current is decidedly higher. To check the ionisation current, connect a microammeter
with an adequate scale “in series” to the ionisation circuit. The high isolation wire that comes from the electrode
must be inserted to the negative (sign -) of the microammeter.
5) With the burner on, adapt delivery to that desired (methane gas = 8550 Kcal/m
3
) by reading the meter. Take
two readings, the second one exactly one minute after the first one. The difference between the two readings
schould be multiplied by in order to obtain the flow per hour (60 minutes). This output can be modified by
operating the special regulator incorporated in the valve (see the last pages for a desciption of how to regulate
the valves).
6) Control that combustion occurs correctly by using the appropriate instruments (CO
2
= about 10% for methane
gas - CO max. = 0.1%).
7) After regulation, turn the burner off and on again several times to check that ignition occurs correctly.
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