Instuctions For Adjustment Of Gas Valve - baltur GI 1000 LX Manual De Instrucciones

INSTRUCTIONS FOR ADJUSTMENT OF GAS VALVE MODEL SKP 75
A flexible membrane divides the valve's cylindrical container into two parts to make two hermetically separated
chambers. One chamber is connected by a small pipe to the burner, in the area between the fan and deflector
disk, so the air pressure in the burner presses on one side of the membrane. Similarly, the other chamber is con-
nected by a small pipe to the gas piping in the area between the valve SKP 75.... and the blast-pipe, so the gas
pressure presses on the other side of the membrane.
By moving, the flexible membrane inevitably balances itself according to the air pressure on one side and the
gas pressure on the other side. The membrane is mechanically connected to the gas flow adjuster (the shutter
of valve SKP 75....) and thus any shift in the membrane caused by pressure changes and combustion air supply,
corresponds to a similar change in pressure and hence supply of gas. In practice, the modulating burner with gas
valve SKP 75...., has an automatic thermal output adjustment system (RWF 40) that acts only on the combus-
tion air regulator damper. To vary the pressure and hence the combustion air flow, gas valve SKP 75.... detects
changes and automatically adjusts gas supply.
ATTENTION
It is clear from the above that changing the air pressure in the burner through the device adjusting the air to the
blast-pipe (changing the air flow diameter) will necessarily and automatically result in a gas supply change.
Example: By reducing the air flow between the combustion head and disk, there is an increase in air pressure
in the burner and a reduction in supply of air in the combustion chamber. Consequently the valve
SKP 75.... detects the pressure increase and increases the supply of gas, so that an adjustment (reduc-
tion) in gas supply is necessary by means of the corresponding devices worked by valve SKP 75.... .
DESCRIPTION OF HOW IT WORKS (see diagram)
With the gas valve closed, i.e. during pre-ventilation and pre-ignition, the fan air pressure acts on the adjuster.
This pressure presses on the membrane's air side, moving it to the left to lever close the ball valve in the servo
control's by-pass. The servo control is thus ready to open the gas valve when it receives voltage from the control
panel and burner control.
When the valve starts to open, the pressure of the gas downstream of the valve increases and so also the pres-
sure on the gas side of the membrane. Since the forces exerted on the membranes are balanced (depending on
the Pg/Pa calibration ratio), the small by-pass ball valve moves to allow a quantity of oil equal to that delivered by
the pump to pass into the by-pass; the servo control piston and the valve are thus balanced. When the modula-
tion device (RWF 40) requires increased supply the air damper steadily opens to increase the air pressure on the
membrane. In this state the previous equilibrium of forces is altered and the adjuster manoeuvres the small ball
valve to obtain steady opening of the gas valve until a new position of equilibrium is obtained according to the
gas/air ratio. The gas/air pressure ratio and hence the gas/air volume remains constant in the whole of the work
field, on condition that the air flow diameter in the burner head is not changed. The term "gas/air ratio" means the
ratio between the pressure of the gas (at the blast-pipe head) and the air pressure (at the blast-pipe head).
When working at low capacity, it is often necessary to increase excess air to obtain the best possible combustion
to make up for less energy in the air/gas mix, .
For these reasons, the adjuster permits a parallel shift in working curve.
DIAGRAM OF THE ADJUSTMENT POSSIBLE
1) Gas/air ratio adjusted for combustion (stoichiometric)
2) Gas/air ratio adjusted for burner's working with excess air.
The percentage of excess air is constant for the whole of the
regulation field.
) Changing the working characteristics at low loads per-
m i t s a n d i n c r e a s e i n t h e e x c e s s a i r p e r c e n t a g e .
Changing possible characteristics for "excess air" and for "lack
of air".
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REV.: 13/09/2007