Maintenance includes the combination of all technical and corresponding administrative, managerial, and supervision actions such as tests, measurements, adjustments, and parts replacement, performed specifically to prevent difficulties from occurring.
Preventive maintenance is the care and servicing by personnel for the purpose of maintaining equipment and facilities in satisfactory operating condition by providing for systematic inspection, detection, and correction of incipient failures either before they occur or before they develop into major defects.
While preventive maintenance is generally considered to be worthwhile, there are risks such as equipment failure or human error involve, just as in any maintenance operation. Preventive maintenance as scheduled overhaul or scheduled replacement provides two of the three proactive failure management policies available to maintenance engineers. Common methods of determining what preventive maintenance (or other) failure management policies should be applied are; Original Equipment Manufacturer recommendations, requirements of codes and legislation within a jurisdiction, what an "expert" thinks ought to be done, or the maintenance that's already done to similar equipment. However Reliability Centered Maintenance, provides the most rigorous and method to determine applicable and effective failure management policies - which may include preventive maintenance tasks - for an item.
To make it simple:
- Preventive maintenance is conducted to keep equipment working and/or extend the life of the equipment.
- Corrective maintenance, sometimes called "repair", is conducted to get equipment working again.
The primary goal of maintenance is to avoid or mitigate the consequences of failure of equipment. This may be by preventing failure before it actually occurs which preventive maintenance and condition based maintenance help to achieve. It is designed to preserve and restore equipment reliability by replacing worn out components before they actually fail. Preventive maintenance activities include partial or complete overhauls at specified periods, oil changes, lubrication and so on. In addition, workers can record equipment deterioration so they know to replace or repair worn out parts before they cause system failure. The ideal preventive maintenance program would prevent all equipment failure before it occurs.
Predictive maintenance is a set of techniques which help determine the condition of in-service equipment in order to predict when maintenance should be performed. This approach offers cost savings over routine or time-based preventive maintenance, because tasks are performed only when warranted.
The "predictive" component of predictive maintenance stems from the goal of predicting the future trend of the equipment's condition. This approach uses principles of statistical process control to determine at what point in the future maintenance activities will be appropriate.