Four Task Categories To Understand In Undertaking Preventive Maintenance (1/4)

By Mac Smith and Glenn HinchcliffePlant Engineering - December 1, 2005

There are four basic factors behind the decision to define and choose preventative maintenance actions:
1. Prevent or mitigate failure occurrence
2. Detect onset of failure
3. Discover a hidden failure
4. No nothing, because of value limitations

By identifying the four factors for doing preventive maintenance, we have also set the stage for defining the four task categories from which a PM action may be specified. These task categories, by one name or another, are universally employed in constructing a PM program, irrespective of the methodology that is used to decide what PM should be done in the program.

The four task categories are as follows:
1. Time-directed (TD): aimed directly at failure prevention or retardation.
2. Condition-directed (CD): aimed at detecting the onset of a failure or failure symptom.
3. Failure-finding (FF): aimed at discovering a hidden failure before an operational demand.
4. Run-to-failure (RTF): a deliberate decision to run to failure because the others are not possible or the economics are less favorable.