24
REGULATION OF AIR AT THE COMBUSTION HEAD (see BT 8608/1)
The combustion head is fitted with a regulation device that closes (moves forward) or opens (moves back) the air
gap between the disc and the head. In this way, when the gap is closed high pressure can be obtained upstream
of the disc, even with low delivery. The high speed and turbulence of the air allows it to penetrate the fuel better,
creating an excellent mixture and providing a stable flame. It may be essential to have a high air pressure upstream
of the disc to prevent the flame from flickering. This is practically indispensable when the burner is working in a
pressurised firebox and/or at high thermal loads. Therefore, it is clear that the device that shuts off the air at the
combustion head must be positioned in such a way as to always keep the air pressure behind the disc at a
significantly higher level. It is advisable to adjust it in order shut off the air to the head, so that the air lock
controlling the intake for the fan opens significantly. Obviously, this must be checked when the burner is working
at the maximum delivery required. In practice, regulation must begin using the device that closes the air to the
combustion head in an intermediate position, and the burner must be ignited to allow regulation as described
above.When the maximum delivery required has been reached, the position of the device that shuts off the air to
the combustion head must be corrected, by moving it forward or back to provide an adequate air flow with the air
lock for the air intake, considerably open. When reducing the air passage in the combustion head, care must be
taken not to close it altogether. Make sure it is perfectly centred in relation to the disc.
If it is not properly centred on the disc, poor combustion and overheating of the head could occur, resulting in its
rapid deterioration. This check is made by watching the LED on the back of the burner and then tightening the
screws that lock the regulator for the air to the combustion head, in position.
N.B. Make sure that ignition occurs correctly because if the regulator has moved forward the speed of the air
coming out may be so high that it makes ignition difficult. If this should occur, move the regulator further
back a little at a time, until a position is reached where ignition occurs regularly, and accept this as the
permanent position.It is preferable to limit the amount of air for the 1st flame to as little as possible, to
ensure ignition, even under the most demanding conditions.
READING GAS (METHANE) METER
When the burner is operating at maximum output, check that the quantity of gas delivered is necessary for the
boiler’s needs. The low calorific value for methane gas is about 8550 kcal/m
3
. To find out the low calorific values
of other types of gas, contact the Gas Distributing Company. Delivery per hour should be taken at the meter.
When checking delivery make sure that gas is not being consumed by other users.If the gas delivery pressure at
the meter is not above 400 mm.w.c., take into consideration the value indicated by the meter without correcting it.
For a first indication, turn on the burner and when it arrives at nominal delivery, measure the gas output in one
minute exactly (the difference between the two readings should be one minute exactly from one to the other.
Multiply this value by 60 in order to obtain the output for 60 minutes (one hour).
The output measured is considered the actual value if the meter reads a pressure below 400 mm.w.c. If the
pressure is more than 400 mm.w.c., the value read must be multiplied by a correction coefficient, as previously
described. Subsequently, multiply the delivery per hour (m
3
/h) by the gas calorific value to obtain the potentiality
delivered in kcal/h; this should correspond or be very near to that requested for the boiler (low calorific value for
methane gas = 8550 kcal/m
3
). Do not allow the burner to operate for a long time (only a few minutes) if the output
exceeds the maximum allowed for the boiler, to avoid possible damage to it; it would be timely to stop the burner
immediately after having taken the two meter readings.
Correcting the value indicated by the meter
If the meter measures the gas delivery at a pressure above 400 mm.w.c., it is necessary to multiply the value by
a correction coefficient. As an indication, the correction coefficient values to be adopted in function with the gas
pressure existing at the meter, can be determined in the following way:
Add to number 1 (one) the number which expresses the gas pressure value in bar, existing at the meter.
Example n°1: Gas pressure at the meter = 2 bar, the multiplication coefficient is 1 + 2 = 3. Therefore, if the meter
reads a delivery of 100 m
3
/h, multiply it by 3 to obtain the actual output which is 100 m
3
/h x 3 = 300 m
3
/h.
Example n°2: Gas pressure at the meter = 1,2 bar, the multiplication coefficient is 1 + 1,2 = 2,2. Therefore, if the
meter reads a delivery of 100 m
3
/h, multiply it by 2,2 to obtain the actual output which is 100 m
3
/h x 2,2 = 220 m
3
/h.
Example n° 3: Gas pressure at the meter = 0,3 bar, (3000 mm.w.c.), the multiplication coefficient is 1 + 0,3 = 1,3.
Therefore, if the meter reads a delivery of 100 m
3
/h, multiply it by 1,3 to obtain the actual output which is 130 m
3
/h.
Example n°4: Gas pressure at the meter = 0,3 bar, (600 mm.w.c.), the multiplication coefficient is 1 + 0,06 = 1,06.
Therefore, if the meter reads a delivery of 100 m
3
/h, multiply it by 1,06 to obtain the actual output which is 100 m
3
/h x
1,06 = 106 m
3
/h.
