13
Dival SQD-1 - MT 234-E - 02-2020
EN
INSTALLATION
The slam-shut valve LA/.. consists essentially of an obturator (fig. 7) fitted on a stem, a releasing lever system, a con
-
trol head and a manual resetting system. The pressure to control Pd, in chamber C of the control head, acts on the
diaphragm 46 which is integral with the cam shaft 45.
The load of the pressure Pd on the diaphragm is countered by the springs 34 and 35 which respectively determine
intervention for pressure increase and pressure decrease. The device is set by turning the rings 17 and 18. Turning the
rings clockwise increases the intervention value; turning anticlockwise decreases it.
Intervention as a result of a pressure increase occurs as follows: when the pressure Pd exceeds the set point the load
on the diaphragm 4 increases until it overcomes the resistance of the spring 34. This causes the shaft 45 to translate
towards the left so that the cam shifts the feeler 33 and trips the lever mechanism 29. In this way, the stem 5 with the
obturator 19 is freed and closed by the spring 8.
IOn the other hand, intervention as a result of a pressure decrease occurs as follows: as long as the pressure Pd stays
above the load of the spring 35, the spring support 13 rest on the support 12.
If the pressure Pd drops below the set point, the spring 35 translates the support 13 to the right and with it the shaft
45.
The cam shifts the feeler 33 and trips the lever mechanism 29. The slam-shut is reset by unscrewing the bushing 7 and
pulling it downwards until the lever system 29 is reset.
During the first phase of the operation, it will be necessary to wait until the upstream pressure, through the internal
by-pass, passes downstream from the obturator to rebalance it. After resetting, the bushing 7 must be screwed back
to its seat.
It is possible to see from the outside whether the slam-shut is open or closed by observing the position of the nut 37
through in the bushing 7, as shown in figure 7.
Table 3 lists the range of intervention of the pressure switches available.
LA/BP SLAM-SHUT SPRING CHARACTERISTICS
Code
Colour
De
Lo
d
Setting range in mbar
Intervention for max. pressure
64470112 RO
RED
34
43
2.2
30 ÷ 50
64470115GR
GREY
42
2.8
50 ÷ 180
Intervention for min. pressure
64470024BI
WHITE
15
45
1.3
6 ÷ 60
LA/MP SLAM-SHUT SPRING CHARACTERISTICS
Code
Colour
De
Lo
d
Setting range in mbar
Intervention for max. pressure
64470115GR
GREY
34
42
2.8
140 ÷ 180
64470116GI
YELLOW
40
3.2
180 ÷ 280
64470051BI
WHITE
50
3.2
280 ÷ 450
Intervention for min. pressure
64470024BI
WHITE
15
45
1.3
10 ÷ 60
6470038GI
YELLOW
40
2
60 ÷ 240
De = external diameter d = wire diameter Lo = Length
LA/.. Slum-Shut
Tab. 3
3.2
LA/… SLAM-SHUT SETTING SPRINGS
