Gas Valve Seal Control Devices - baltur COMIST 36 Instrucciones

LDU 11.. GAS VALVE TIGHTNESS CONTROL EQUIPMENT
Use
LDU 11 equipment is used to verify
tightness of valves on natural gas
burners.
The LDU 11 combined with a normal
pressure switch automatically veri-
fies tightness of natural gas burners
valves, before every start up and
immediately after each stop.
Tightness control is carried out by
two-stage verification of gas circuit
pressure in the section between the
two burner valves.
Operation
During the first stage of the tight-
ness 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 achie-
ved 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 at-
mospheric 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 pres-
sure into the pipeline ("filling opera-
tion"). 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.The-
refore 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-connec-
tion for terminals 4 and 5 - contact
III - terminal 6).
This is the circuit that usually ena-
bles the equipment start-up control
circuit. After circuit between termi-
nals 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 pro-
grammer'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 posi-
tion
In plants without a bleed
valve = test circuit put un-
der 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 un-
der pressure by opening
of relief valve
69 / 139
0006080093_00709
TEST 2 "TEST " pipeline at gas
pressure (blow-by verifi-
cation of valve on furnace
side of burner)
III
Automatic zero (or ino-
perative 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 pro-
grammer automatically returns to
rest position, and is ready to carry
out a further programme for che-
cking tightness of valves as they
close.