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• Enter a typical value for P in the PID parameter in ValVue. SVI3 factory value for P
is 1
0
0; if it is a large valve this may need to be higher to start
.
In Setup mode enter
large value for P and run Autotune again (See Table 12).
7.3 Tight Shutoff
7.3.1 Tight Shutoff Application to Protect from Seat Erosion
The Tight shutoff feature can be programmed to prevent valve seat erosion using the full
actuator force to eliminate damaging leakage. At a position setpoint of 2%, for example,
this function allows full thrust to occur when the input signal is less than 2%. This solves a
common cause of valve repair. Do not use tight shutoff if it is necessary to throttle the
valve at very small flows.
7.3.2 Tight Shutoff Application to High Pressure Liquid Letdown Valve Trim
When staged trim is used in High Pressure Liquid Letdown Valves, Tight Shutoff can be
adjusted to move the valve from the seat to begin throttling at the minimum operable CV
level. Using the tight shut-off feature in SVI3 prevents valve seat damage that can occur
when throttling at clearance flows. See recommended Tight Shutoff settings in the
following table. Tight shutoff can be adjusted with pushbuttons or with ValVue or a HART
®
communicator.
7.4 Using SVI3 DTM Diagnostics
SVI3 advanced features are simple to use with SVI3 DTM software. The following
examples illustrate some uses. Please refer to SVI3 DTM Manual full Valve Diagnostics
Procedures and information.
Table 21: Tight Shutoff Parameters for High Pressure Liquid Letdown Trim
Masoneilan Valve
Type
Valve Trim Type
Set Tight Shutoff
Positioner
Characteristics
Lincoln Log
Any
15%
Linear
41000 VRT Type S
Partial Stack
6%
Linear
41000 VRT Type S
Full Stack
3.5%
Linear
41000 VRT Type C
Cage
6%
Linear
28000
Varilog
5%
Linear
Any
Class V Shutoff
2%
Linear
