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Technical Manual MT 188-E
3.0 ACCESSORIES
3.1
"PUSH" THREE-WAY SWITCH VALVE
The "Push" valve is a three-way switch valve with spring return. With
knob 1 set to the normal operation position, the ways A and B are angle
communicating; while way C is excluded.
With the knob pressed downwards, in "check" position, the ways A and
C are communicating, while way B is excluded. When the knob 1 is
released, the communication between the ways A and B is
automatically restored due to the tripping of the spring D.
1
Fig. 8
1
Fig. 9
This valve is usually installed in the impulse line of safety devices
against pressure increase and/or decrease (SAV or SBV) in order to be
able to verify their calibrations in a very short time without
disconnecting the impulse pipe during the periodic checks.
The application of this accessory involves, during normal operation,
that the pressure switch head (or the pilot of the safety device)
receives the signal of the pressure to be kept monitored and controlled
through the ways A and B. In the control phase, the control head
receives a signal from an auxiliary external controlled pressure from
way C to way A. Once the check has been performed, when the knob
returns to the normal operation position, the connection between the
area with the pressure to be monitored and controlled and the head of
the safety device is restored automatically, thus avoiding the on/off
switching of the device, which may happen due to a sheer oversight, if
the three-way valve is of the normal type with manual operation. As a
consequence, the "Push" device is a second safety device, which
assures the non-exclusion of the main safety device and allows its
periodical check.
4.0
COMMISSIONING
4.1
GENERAL
After the installation, verify that the on/off valves at inlet and outlet, any
available bypass valve on the line, and the relief valve to the
atmosphere are closed.
Before commissioning, it is recommended to verify that the use
conditions do meet the features of the equipment.
Such features are given on the rating plates present on the equipment
itself.
It is recommended to enable the opening and closing on/off valve very
slowly. Too fast maneuvers may cause the involuntary tripping of the
device or damage the valve.
EQUIPMENT RATING PLATES
Here below there is the list of the symbols used
together with their meaning
= Compliance with Directive 97/23/EC (PED)
Pumax = maximum operation pressure at device inlet.
PS = maximum allowable pressure that can be born under safety
conditions by the device body structure.
AG = tripping accuracy.
Wdso = tripping range due to slam-shut valve overpressure, which can
be obtained by using the setting spring mounted during final testing.
Wdo = tripping range due to slam-shut valve overpressure, which can
be obtained by using the setting springs listed in the tables.
7
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