GE EVT-Pro 2.0, Operation And Technical Manual, Page: 27 / 60

SECTION 21
EVT PRO 2.0
®
- EXPLANATION OF GRAPH
Explanation of Graph
In Situ PRV testing enables the technician to accurately determine the
PRV’s set pressure
without removing the PRV from the installation. The test result obtained during in situ
testing is considered the
‘hot set pressure’, not the ‘cold set pressure’, given that normal
operating conditions are present during testing.
During in situ testing, hydraulic force is applied to the PRV spindle, fractionally lifting the
disc off the seat. An installed force transducer, records the hydraulic force necessary to lift
the disc from the seat. The EVT PRO 2.0
®
combines this measurement with an indication
of lift and an increase in sound produced by flow through the PRV to determine the PRV
set pressure.
Graphic evaluation of the hydraulic force, lift, and sound enables the technician to
accurately determine the PRV set pressure (Fig. 21.1).
Figure 21.1
– Example of Valve Test Graph Results
Hydraulic Force Line
– During testing, the hydraulic force gradually increases. When the
PRV is closed, inlet pressure applies a static force on the disc contained between the area
of the nozzle and disc seat. Upon opening, media flow applies an additional kinetic force on
the disc against a larger area known as the huddling chamber. This additional kinetic force
along with the greater area now exposed to the pressure, causes a momentary decrease to
the measured hydraulic force as indicated in the graph.
As set point is reached you
should see changes in the
track of each sensor, such as
changes in load, lift, acoustics,
etc.
Where these changes
correlate and align is a very
good indication of set point.
EVT PRO 2.0
®
Operations and Technical Manual (Rev 1.0
– 2016)
NOT FOR COPY OR DISTRIBUTION Page 23