3
TECHNICAL MANUAL ICM
3L.P. GAS s.r.l.
1.0
INTRODUCTION
The scope of this manual is to provide the essential
information for the installation, commissioning and
maintenance of ICN slam-shut valves.
It is also appropriate to provide a brief illustration of
the main features of the valves and of its accessories.
1.1
MAIN FEATURES
This is a device wich immediately blocks the gas flow
if, following some kind of failure, the downstream
pressure reaches the set-point for its intervention or if
it is operated manually.
The main characteristics of the slam-shut device are:
• design pressure: 18.9 bar for all the components;
• intervention with pressure increase and/or
decrease;
• precision (AG): ± 1% of the pressure set-point for
pressure increases, ± 5% for pressure decreases;
• incorporated by-pass for balancing the pressures
and facilitating the resetting of the device;
• push-button manual control.
1.2
OPERATION
The slam.shut mechanism (Fig. 1) consists of:
• a mobile obturator A with sealing gaskets subject
to the load of the closing spring G;
• a lever assembly L whose rotation causes the
movement of the obturator A;
• a pressure switch device I-N whose internal motion
determines the open or closed position of the
obturator A.
The pressure switch device (Fig. 2) comprises a con-
trol head 11 in which the pressure to control Pa acts
on the diaphragm 21 which is integral with the shaft
with cams 18.
The load of the pressure Pa on the diaphragm is
contrasted by the springs 14 and 15, which respectively
determine intervention for a pressure increase or
decrease. The slam-shut device is set by adjusting
the rings 12 and 13.
The intervention value is increased by turning the rings
clockwise and vice versa when turned anticlockwise.
In the case of intervention for pressure increase, when
the Pa exceeds the setpoint, the load on the diaphragm
21 of the control head B increases until it overcomes
the resistance of the spring 14.
This provokes the downward displacement of the shaft
18 which shifts the feeler 19 and releases the lever
mechanism 20 by means of the cam 23.
Intervention for a pressure decrease takes place as
follows.
As long as the value of Pa stays above the set load of
the spring 15, the spring support 17 rests on support
16.
If the pressure Pa drops below the setpoint, the sup-
port of spring 16 stops its stroke on the beat of the
body 5 and the spring 15 displaces the support 17
upwards and the shaft 18 as a result. The cam 24 then
shifts the feeler 19 and causes the release of the lever
mechanism 20.
Intervention of the slam-shut device can also be
provoked manually by means of the release button
22. The connection between the control head 11 and
the Pa control point can be made with the intrposition
of a device “Push” Fig. 8 which makes it easy to control
the operation of the pressure control device.
Fig. 1
Fig. 2
