Key To Symbols - baltur COMIST 72 DSPGM Manuel D'installation, Utilisation Et Entretien

LDU 11.. GAS VALVE TIGHTNESS CONTROL
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EQUIPMENT
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Use
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LDU 11 equipment is used to verify tightness of valves
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on natural gas burners.
The LDU 11 combined with a normal pressure switch
I automatically verifies tightness of natural gas burners
valves, before every start up and immediately after each
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stop. Tightness control is carried out by two-stage ve-
rification of gas circuit pressure in the section between
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the two burner valves.
Operation
During the first stage of the tightness control (TEST 1),
the pipeline between the valves being checked must be
at atmospheric pressure. In plant without atmospheric
pressure setting pipes, this pressure is achieved by
tightness control equipment. The latter opens the valve
on the furnace side for 5 seconds during "t4" time.
When the 5 seconds are up, the furnace side valve
is closed. During the first phase (TEST 1) the control
equipment ensures that atmospheric pressure in the
pipes is kept constant.
Surveillance is carried out by the "DW" thermostat.
If there is blow-by in the safety valve while closing,
pressure increases and as a result the "DW" pressure
switch operates. For this reason, in addition to indicating
pressure, the equipment goes into fault state and the
position indicator stops blocked in the "TEST 1" position
(red pilot lamp lit).
Vice-versa, if pressure does not increase because
there is no blow-by in the relief valve as it closes, the
equipment immediately programmes the second stage
"TEST 2".
Under these conditions, the relief valve opens for 5
seconds during "t3" time and introduces gas pressure
into the pipeline ("filling operation"). During the second
verification stage, this pressure must remain constant.
Should it drop, this means that the burner on the furnace
side has a blow-by (fault) when closing.Therefore the
"DW" pressure switch operates and the tightness control
equipment prevents burner start-up and stops in blocked
state (red pilot lamp lit). If second stage verification
is positive, the LDU 11 equipment closes the internal
control circuit between terminals 3 and 6 (terminal 3 -
contact ar2 - outer cross-connection for terminals 4 and
5 - contact III - terminal 6). This is the circuit that usually
enables the equipment start-up control circuit. After
circuit between terminals 3 and 6 has closed, the LDU
11's programmer returns to rest position and stops. This
means it enables fresh verification without changing the
position of the programmer's control contacts.
N.B.
Adjust the "DW" pressure switch to about half
the pressure of the gas supply network.

Key to symbols:

} Start-up = operating position
In plants without a bleed valve = test circuit
put under atmospheric pressure by opening of valve
on the
furnace side of the burner.
TEST 1 "TEST 1" pipeline at atmospheric pressure
(blow-by verification at closure of relief valve)
Putting test circuit gas under pressure by
opening of relief valve
TEST 2 "TEST 2" pipeline at gas pressure (blow-by
verification of valve on furnace side of burner)
III Automatic zero (or inoperative mode) reset
of programmer
}
Operation = set for new blow-by verification
If trouble is signalled, there is no voltage in all control
equipment terminals excepting terminals 13 which gives
remote, visual indication of trouble. When verification
is over, the programmer automatically returns to rest
position, and is ready to carry out a further programme
for checking tightness of valves as they close.
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