Page 292 - Root Cause Failure Analysis

CONTROL VALVES

Although there are limited common control valve failure modes, the dominant prob-
lems are usually related to leakage, speed of operation, or complete valve failure.
Table 29-1 lists the more common causes of these failures.
Special attention should be given to the valve actuator when conducting a root cause
failure analysis. Many of the problems associated with both process and fluid-power
control valves really are actuator problems.
In particular, remotely controlled valves that use pneumatic, hydraulic, or electrical
actuators are subject to actuator failure. In many cases, these failures are the reason a
valve fails to properly open, close, or seal. Even with manually controlled valves, the
true root cause can be traced to an actuator problem. For example, when a manually
operated process-control valve is jammed open or closed, it may cause failure of the
valve mechanism. This overtorquing of the valve’s sealing device may cause damage
or failure of the seal, or it may freeze the valve stem. Either failure mode results in
total valve failure.

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