baltur GI MIST 350 DSPGM, Instruction

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0006080103 ed2005/10

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 verifi es tightness of natural gas burners 

valves, before every start up and immediately after each stop.

Tightness control is carried out by two-stage verifi cation of gas circuit pressure in the section between the two 

burner valves.

Operation

During the fi rst 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 fi rst 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 equip-

ment 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 (“fi lling operation”). During the second verifi cation 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 bloc-

ked state (red pilot lamp lit). If second stage verifi cation 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 verifi cation 

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 verifi cation 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 verifi cation of valve on furnace side of burner)

III

Automatic zero (or inoperative mode) reset of programmer

}

Operation = set for new blow-by verifi cation

If trouble is signalled, there is no voltage in all control equipment terminals excepting terminals 

13

 which gives 

remote, visual indication of trouble.

When verifi cation 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.