baltur COMIST 72 DSPGM, Instruction

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DESCRIPTION OF TWO STAGE PROGRESSIVE OPERATION WITH NATURAL GAS FOR
COMIST.....DSPGM
(see N° 0002910610 and N° 0002910640)
CONTROL BOX SPECIFICATIONS
This is referred to as a 2-stage progressive operation because the passage from the 1st flame to the 2nd flame
(from the minimum rate to the maximum pre-established rate) takes place gradually.
The amount of combustion air and fuel delivery are increased very gradually and this ensure stabilization of the
gas feed network pressure.
The field of variation in flow obtainable is from 1 to 1/3.
The burner is fitted with an end-of-the-run switch (a micro-switch) which stops the burner starting up if the flow
regulator is not in the minimum position.
Before ignition, a pre-ventilation of the combustion chamber occurs (according to Regulations) with air open.
At the end of the ventilation phase, if the air ventilation pressure switch has measured sufficient pressure, the
ignition transformer will be connected and subsequently the ignition (pilot) valves and the safety valve will open.
Gas reaches the combustion head, mixes with air supplied by the fan, and is ignited.
Delivery is regulated by the flow regulator incorporated in the ignition flame (pilot) valve.
The ignition transformer is disconnected 3 seconds after the ignition flame and safety valves are inserted.
The burner is now operating with the ignition flame (pilot) only.
Flame presence is detected by a relative control device (ionization probe immersed in the flame, or UV cell).
The relay programmer passes the “shut down” position and gives voltage to the servomotor which regulates the
delivery (gas/air); the burner is now operating at minimum output.
If the boiler thermostat (or pressure switch) of the 2
nd stage allows it (regulated at a temperature or pressure value
superior to that existing in the boiler), the servomotor which regulates the gas/air delivery starts turning and
determines a gradual increase in the gas delivery and in the relative combustion air until it reaches the maximum
delivery value at which the burner has been regulated.
N.B. The “V” cam of the servomotor regulating air/gas delivery (see BT 8562/1) inserts almost immediately the
principle gas valve, which in turn opens completely. Gas delivery is not determined by the principle valve
but by the position of the gas delivery regulation valve (see BT 8816/1 and BT 8813/1).
The burner remains in the maximum delivery position until the temperature or pressure reaches the limit set for the
intervention of the boiler thermostat (or pressure switch) of the 2
nd stage and makes the servomotor regulating
gas/air delivery rotate in the opposite sense of direction.
Thus gas delivery and the relative combustion air are gradually reduced until they reach minimum value.
Even with delivery at a minimum, if the limit (temperature or pressure) at which the shut down device (thermostat
or pressure switch) has been regulated is reached, the burner will be brought to a standstill.
When the temperature or pressure drops below the intervention limit set on the shut down device, the burner will
start up again, according to the programme previously described.
During normal operations, the boiler thermostat/pressure switch of the 2nd stage fitted to the boiler detects the
variations requested and automatically proceeds with adapting the fuel and combustion air delivery by inserting
the servomotor which regulates delivery (gas-air). This will rotate in such a way as to obtain an increase or a
decrease. With this manoeuvre, the gas/air delivery regulating system try to equilibrate the quantity of heat supplied
to the boiler with that which the boiler gives to be utilized.
If the flame does not appear the control box goes to “shut down” (the burner stops completely and the relative
indicator light is turned on).
To unblock the control box, press the appropriate pushbutton.
Control
box &
relative
programmer
LFL 1.333
Cyclic relay
Safety time in
seconds
3
Pre-ventilation
time with shutter
open
in seconds
31,5
Pre-ignition
in seconds
6
Post-ignition
in seconds
3
Time between
1st flame &
modulation start
in second
12