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MT 237 – EN ed.2015 (Rev.A)
3.0 ACCESSORIES
3.1
"PUSH" THREE-WAY SWITCH VALVE
The "push" valve is a three-way switch valve with spring return. With the knob set to the normal operation position, the ways A and B are
angle communicating; while way C is excluded (fig. 6).
Figure 6
With the knob pressed downwards, in "check" position, the ways A and C are communicating, while way B is excluded (fig. 7). W hen the
knob is released, the communication between the ways A and B is automatically restored due to the tripping of the spring D.
Figure 7
This valve is usually installed in the sensing lines 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 sensing pipe during the periodic checks.
The peculiarity of this lies in the fact that, during normal operation, the pressure switch head receives the signal of the pressure to be kept
monitored through the ways A and B. In the control phase, the head receives a signal from an external auxiliary controlled pressure from
way A and C. Once the knob returns to its normal operation position, the connection between the environment with the pressure to be
monitored 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 would be of the normal type with manual operation. In other words, the "push" device is a
second safety device, which assures the non-exclusion of the main safety device and allows its periodical check.
