Preventive Maintenance
Preventive Maintenance (PM) is a proactive strategy where maintenance tasks such as inspection, lubrication, calibration, cleaning, adjustment, and component replacement are performed at predetermined time or usage intervals, regardless of actual equipment condition, to prevent unexpected failure and extend asset life.
In a shop floor maintenance environment using a CMMS like ServiceGrid, PM is applied by scheduling work orders triggered by fixed intervals (e.g., every 500 hours or monthly) to execute routine checks such as belt inspections, filter changes, and lubrication before failure occurs. This approach relies on the statistical assumption that failure probabilities can be determined to replace parts in time to preclude failure, ensuring equipment reliability and reducing unplanned downtime.
- Over-maintenance: Replacing components prematurely because the schedule is not based on actual wear, leading to unnecessary costs and introducing new parts that may fail early.
- Under-maintenance (Fixed Interval Rigidity): Ignoring actual operating conditions (e.g., running a machine 2x harder than the baseline) while sticking to a fixed calendar schedule, causing age-related failures to occur before the next PM.
- Lack of Root Cause Analysis: Using PM merely to fix recurring issues without addressing the underlying cause, resulting in repeated breakdowns and wasted labor on ineffective tasks.
How does PM differ from Predictive Maintenance (PdM)?
PM is time/usage-based and performed regardless of condition, whereas PdM is condition-based, using sensors to monitor specific parameters and only intervening when degradation is detected.
What is the MTTF impact of PM?
PM activities are carried out specifically to reduce the probability of failure or increase the Mean Time to Failure (MTTF) by restoring elements to as-new condition before failure occurs.
When is PM mandatory vs. optional?
PM is mandatory for non-repairable systems where waiting for failure is not an option, whereas for repairable systems, it is an initiative to prevent the need for corrective maintenance.
What is the fundamental assumption of a PM program?
It assumes a cause-and-effect relationship between scheduled maintenance and operating reliability, assuming failure probabilities are statistically determinable.