Page 261 - Intro Predictive Maintenance

252 An Introduction to Predictive Maintenance

Table 10–18 Common Failure Modes of Control Valves

THE PROBLEM

Valve Fails to Open Valve Fails to Close Leakage through Valve Leakage Around Stem Excessive Pressure Drop Opens/Closes Too Fast Open/Closes Too Slow

THE CAUSES
Dirt/Debris Trapped in Valve Seat
Excessive Wear
Galling

Manually Actuated Line Pressure Too High
Mechanical Damage

Not Packed Properly

Packed Box Too Loose

Packing Too Tight
Threads/Lever Damaged

Valve Stem Bound

Valve Undersized
Dirt/Debris Trapped in Valve Seat
Pilot Actuated Mechanical Damage (Seals, Seat)

Galling

Pilot Port Blocked/Plugged

Pilot Pressure Too High
Pilot Pressure Too Low
Corrosion
Solenoid Actuated Galling
Dirt/Debris Trapped in Valve Seat

Line Pressure Too High

Mechanical Damage

Solenoid Failure

Solenoid Wiring Defective

Wrong Type of Valve (N-O, N-C)
Source: Integrated Systems, Inc.
Misalignment
Physical misalignment of a shaft will either cause seal damage or permit some leakage
through the seal, or it will result in total seal failure. Therefore, it is imperative that
good alignment practices be followed for all shafts that have an installed mechanical
seal.