11
MT 237 – EN ed.2015 (Rev.A)
4.2
GAS FEEDING, CHECK OF EXTERNAL TIGHTNESS AND CALIBRATIONS
Pressure feeding to the equipment shall be performed very slowly. Where no specific speed procedure is implemented, it is recommended
to keep the gas speed in the feeding piping under a value of 5 m/sec, during the pressure feeding phase.
In order to prevent the equipment from being damaged, the following shall be absolutely avoided:
Pressurization through a valve positioned downstream of the equipment itself.
Depressurization through a valve positioned at inlet of the equipment itself.
The external tightness is assured when, by applying a foam medium on the element under pressure, no bubbles are produced.
Usually, the equipment is supplied already calibrated to the requested value.
Moreover, it may happen that due to several reasons (e.g. vibrations during transport) the calibrations may be subject to slight changes,
though remaining within the range of the values allowed by the springs used. Therefore, it is advisable to verify the calibrations according to
the procedures outlined here below.
Before commissioning the device, it is necessary to verify that all on/off valves (inlet, outlet, and bypass - if any) are closed and
that the gas has such a temperature as not to create malfunctions.
4.3
EXTERNAL TIGHTNESS AND CALIBRATIONS CHECK
A.
For the slam-shut devices connected to the downstream piping through the "push" three-way switch valve, proceed as follows:
Figure 9
1.
Connect a controlled auxiliary pressure to the "push" valve (way C);
2.
Stabilize this pressure at the calibration value set for the regulator;
3.
Completely press the knob 1 of the "push" three-way valve;
4.
Restore the slam-shut device by means of the suitable bushing;
5.
Keep the knob 1 pressed and:
For safety devices tripping in case of maximum pressure: slowly increase the auxiliary pressure and verify the tripping
value. If necessary, increase the tripping value by rotating clockwise the adjustment ring nut 549; rotate it counter-
clockwise to decrease the tripping value.
For safety devices tripping in case of pressure increase and decrease: slowly increase the auxiliary pressure and
record the tripping value. Restore the pressure to the calibration value of the regulator and perform the block
restoration operation. Check the tripping due to pressure decrease by slowly reducing the auxiliary pressure. If
necessary, increase the values for tripping in case of pressure increase or decrease by turning clockwise the ring
nuts 549 or 548, respectively. Proceed inversely to decrease the tripping values.
Make sure that the operation is correct by repeating the procedure for at least 2-3 times
6.
Disconnect the controlled auxiliary pressure from way C;
