Masoneilan SVI3 Installation and Maintenance Manual
=
| 111
© 2021 Baker Hughes Company. All rights reserved.
7.4.2 Continuous Diagnostics
SVI3 continuously gathers critical information that can be used to predict maintenance
intervals for control valves. These are:
• Total Travel
• Number of cycles
• Time open
• Time closed
• Time near closed
7.4.3 Monitoring a Valve Bellows Seal
The SVI3 automatically stores the accumulated valve stroke reversals, as Number of
cycles. ValVue can be used to periodically retrieve the values and to track the remaining
life of a bellows seal or packing. Total travel can also be used to estimate the remaining
life of packings and seals.
7.4.4 Critical Service, Cavitation Control Trim
The time near closed, of a valve with severe service when near the seat, can be
monitored by ValVue and saved to permanent files to monitor and predict maintenance
needs. You can use ValVue to specify the criterion for time-spent-near-closed (a valve
position such as 4%, for example). See also Tight shutoff- Application to High Pressure
Liquid Letdown Valve Trim.
7.4.5 Diagnostic Valve Tests
The standard diagnostic test performs a full stroke test, and determines stroking speed.
The Step Response test moves the valve between several points selected by you and
graphically presents the dynamic response for each step. The Positioner Signature test
strokes the valve over a travel specified by you and records a signature for comparison
with the as-built and with future tests to predict maintenance intervals. The full version of
ValVue is required for diagnostic tests.
7.5 Determining an SVI Positioner Compliance Voltage in a
Control System
This discussion explains how to determine compliance voltage for an SVI3 positioner.
A definition of compliance voltage is: The voltage that must be available at the control
system output in order to drive the control current through the SVI3 and all the resistive
devices in series with it.
