Table 1: Faults to be detected and isolated.


f1Valve clogging
f2Valve or valve seat sedimentation
f3Valve or valve seat erosion
f4Increasing of valve or bushing friction
f5External leakage
f6Internal leakage (valve tightness)
f7Medium evaporation or critical flow
f8Twisted servomotor's piston rod
f9Servomotor's housing or terminals tightness
f10Servomotor's diaphragm perforation
f11Servomotor's spring fault
f12Electropneumatic transducer fault
f13Rod displacement sensor fault
f14Pressure sensor fault
f15Positioner feedback fault
f16Positioner supply pressure drop
f17Unexpected pressure change across the valve
f18Fully or partly opened bypass valves
f19Flow rate sensor fault