Flowserve Logix MD+ ValveSight - Manual (Page 94)

ValveSight™ Diagnostics DTM Manual for Logix MD+ Positioner with HART®
FCD- LGENSF0014-00
© Flowserve Corporation
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limit.
•
Implications: Low supply pressure can cause poor valve response or
positioner failure. The minimum recommended supply pressure for
proper operation is 1.3 bar (19 PSI).
•
Possible Solutions: Regulate the supply pressure at the positioner
above 1.3 bar (19 PSI). Ensure system air/gas supply is
adequate. Repair kinked or restricted supply tubing. Check for
pneumatic leaks in the actuator and actuator tubing. Recalibrate
pressure sensors. Check the pressure sensor board connections and
replace pressure sensor board if necessary.
Actuation Ratio
•
Definition: The force required to control the system is close to the
maximum available force.
•
Implications: Actuation Ratio is based on the ratio of available force to
the required force to actuate. Control may be lost if this ratio reaches
100%. It is affected by the process load, friction, spring force, and
available supply pressure.
•
Possible Solutions: Increase the supply pressure. Reduce the
friction. Check the actuator spring. Resize the actuator. Adjust user
set limits.
Spring Fail
•
Definition: Upon loss of air supply, the valve may not move to the fail-
safe position.
•
Implications: The spring alone is not adequate to overcome the friction
and process load in the system. The system is relying on pneumatic
force to actuate in the direction the spring is pushing. The failsafe
spring may have failed, or it was not sized properly for the application.
Friction or process load may have increased.
•
Possible Solutions: Repair or replace actuator spring. Check for high
friction. Reduce process load.
Pneumatic Leak
•
Definition: The positioner has detected a leak in the actuation
assembly.
•
Implications: Leakage from the actuator can cause decreased
responsiveness and excessive air/gas consumption.
•
Possible Solutions: Repair pneumatic leaks at the tubing junctions
and actuator seals. Check spool valve for excessive wear.