baltur COMIST 180 Manual Installation, Use, Maintenance page 66

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 verifies 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 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.
E
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,
N
in addition to indicating pressure, the equipment goes into fault state and the position indicator stops blocked in the "TEST 1" position (red
G
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 program-
L
mes 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 opera-
I
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.Therefore the "DW" pressure switch
S
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
H
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 program-
mer'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.
28 / 34
0006080095_200902