Quick answer
A good PM task has: (1) a specific action verb (inspect, measure, clean, replace, test — not "check"); (2) an acceptance criterion (what pass/fail looks like); (3) a frequency derived from the failure mode's P-F interval or manufacturer data; (4) a record field for the measured value (not just a tick box). Group tasks by frequency to reduce equipment downtime: weekly route checks, monthly lubrication and filter tasks, annual major inspections. Link each task to a failure mode — tasks with no identifiable failure mode should be removed.
Writing Effective PM Tasks
The most common PM checklist failure: vague task descriptions that technicians cannot execute consistently. Compare:
| Poor task (ineffective) | Good task (effective) |
|---|
| "Check motor bearings" | "Measure bearing housing temperature with contact thermometer at DE and NDE bearing locations. Record in °C. Alert limit: >80°C or >40°C above ambient" |
| "Inspect coupling" | "Inspect coupling element for cracks, hardening, or uneven wear. Replace if element shows surface cracking, hardness rating <Shore A 50, or element thickness reduced by >20%" |
| "Check oil level" | "Check gearbox oil level via sight glass. Top up to mid-level mark with ISO VG 220 mineral gear oil (same as in use). Record level: Low/OK/High" |
| "Grease bearing" | "Apply 9 g (approx. 3 pumps standard gun) of Mobilith SHC 460 grease to bearing housing via zerk fitting. Run machine; confirm no temperature rise above pre-grease baseline within 30 min" |
Setting PM Frequency
PM task frequency should be set based on the P-F interval of the failure mode — the time between when a potential failure becomes detectable and when it becomes a functional failure. The task frequency should be less than half the P-F interval to ensure detection before failure:
| Failure mode | Detection method (P) | Typical P-F interval | Recommended task frequency |
|---|
| Belt wear and cracking | Visual inspection — cracking, fraying, glazing | 1–3 months | Monthly visual inspection |
| Coupling element deterioration | Visual inspection | 3–12 months | Quarterly inspection |
| Gearbox oil degradation | Oil analysis (viscosity, TAN, wear metals) | 3–6 months | Oil sample every 3 months |
| Motor insulation degradation | IR test (megger test) | Years | Annual insulation resistance test |
| Pump impeller wear | Performance measurement (flow vs head) | 3–12 months | Quarterly performance check |
| Filter blockage | Pressure differential measurement | Days to weeks | Weekly or monthly ΔP check |
Electric Motor PM Template
| Task | Frequency | Acceptance criterion |
|---|
| Visual inspection — general condition, cleanliness, terminal box | Monthly | No dirt build-up on fins; terminal box sealed; no oil leaks at shaft seals |
| Bearing temperature measurement (DE and NDE) | Monthly | <80°C absolute or <40°C above ambient temperature |
| Vibration measurement (overall mm/s RMS at DE and NDE) | Monthly or quarterly | ISO 10816 Zone B for machine power class |
| Insulation resistance test (Megger 500V or 1kV) | Annually or after wet conditions | >100 MΩ (new); >1 MΩ (acceptable in service); polarisation index PI >2.0 |
| Bearing regreasing (if grease-lubricated, regreaseable type) | Per calculated interval (typically 3–12 months) | Correct grease type, correct quantity (per formula); no temp rise after greasing |
| Coupling inspection and alignment check | Annually | Parallel alignment <0.05 mm; angular alignment <0.05 mm per 100 mm; coupling element in good condition |
| Winding resistance measurement (3-phase balance) | Annually or after repair | ±2% maximum imbalance between phases |
Centrifugal Pump PM Template
| Task | Frequency | Acceptance criterion |
|---|
| Visual inspection — leaks from mechanical seal or gland, bearing housing, couplings | Weekly | No seal leakage beyond acceptable drip rate (gland: 1–3 drops/min acceptable; mechanical seal: zero); no bearing housing oil leaks |
| Bearing housing oil level check | Weekly | Mid-level in sight glass |
| Bearing temperature measurement | Monthly | <70°C bearing housing; <30°C above oil temperature |
| Vibration measurement (overall, all three axes) | Monthly or quarterly | ISO 10816-7: B/C boundary per pump class |
| Performance check: measure flow and pressure, compare to pump curve BEP | Quarterly | Flow within ±10% of design point; pressure head within ±5% |
| Bearing housing oil change | Annually or per oil analysis | ISO VG 68 or 100 per OEM spec; clean oil, correct level |
| Mechanical seal inspection (visual and performance) | Annually | No leakage; no face wear visible; flush pipe clear |
CMMS Integration
PM checklists are only effective if they are executed, recorded, and reviewed. CMMS (Computerised Maintenance Management System) integration requirements:
- Each task generates a work order automatically at the correct interval — calendar-based or meter-based (hours/starts)
- Measured values are recorded in the work order (not just Yes/No ticks) — enables trending of bearing temperatures, vibration levels, oil levels over time
- Exception flags: task acceptance criteria are coded as pass/fail thresholds — CMMS generates a corrective work order automatically if a threshold is exceeded
- Compliance tracking: PM compliance rate (% of PMs completed on time) should target >95% for critical assets — tracked as a KPI
- Feedback loop: corrective work orders arising from PM inspections are linked to the originating PM work order — this data drives PM content improvement over time